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Barney BM. Azotobacter vinelandii. Trends Microbiol 2024; 32:1034-1035. [PMID: 39168789 DOI: 10.1016/j.tim.2024.07.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2024] [Revised: 07/11/2024] [Accepted: 07/12/2024] [Indexed: 08/23/2024]
Affiliation(s)
- Brett M Barney
- Department of Bioproducts and Biosystems Engineering and Biotechnology Institute, University of Minnesota, St Paul, MN 55108, USA.
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2
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Swindell J, Dos Santos PC. Interactions with sulfur acceptors modulate the reactivity of cysteine desulfurases and define their physiological functions. BIOCHIMICA ET BIOPHYSICA ACTA. MOLECULAR CELL RESEARCH 2024; 1871:119794. [PMID: 39033933 DOI: 10.1016/j.bbamcr.2024.119794] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2024] [Revised: 06/21/2024] [Accepted: 07/11/2024] [Indexed: 07/23/2024]
Abstract
Sulfur-containing biomolecules such as [FeS] clusters, thiamin, biotin, molybdenum cofactor, and sulfur-containing tRNA nucleosides are essential for various biochemical reactions. The amino acid l-cysteine serves as the major sulfur source for the biosynthetic pathways of these sulfur-containing cofactors in prokaryotic and eukaryotic systems. The first reaction in the sulfur mobilization involves a class of pyridoxal-5'-phosphate (PLP) dependent enzymes catalyzing a Cys:sulfur acceptor sulfurtransferase reaction. The first half of the catalytic reaction involves a PLP-dependent CS bond cleavage, resulting in a persulfide enzyme intermediate. The second half of the reaction involves the subsequent transfer of the thiol group to a specific acceptor molecule, which is responsible for the physiological role of the enzyme. Structural and biochemical analysis of these Cys sulfurtransferase enzymes shows that specific protein-protein interactions with sulfur acceptors modulate their catalytic reactivity and restrict their biochemical functions.
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Affiliation(s)
- Jimmy Swindell
- Department of Chemistry, Wake Forest University, Winston-Salem, NC, 27109, United States of America
| | - Patricia C Dos Santos
- Department of Chemistry, Wake Forest University, Winston-Salem, NC, 27109, United States of America.
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3
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Koch H, Sessitsch A. The microbial-driven nitrogen cycle and its relevance for plant nutrition. JOURNAL OF EXPERIMENTAL BOTANY 2024; 75:5547-5556. [PMID: 38900822 DOI: 10.1093/jxb/erae274] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2023] [Accepted: 06/18/2024] [Indexed: 06/22/2024]
Abstract
Nitrogen (N) is a vital nutrient and an essential component of biological macromolecules such as nucleic acids and proteins. Microorganisms are major drivers of N-cycling processes in all ecosystems, including the soil and plant environment. The availability of N is a major growth-limiting factor for plants and it is significantly affected by the plant microbiome. Plants and microorganisms form complex interaction networks resulting in molecular signaling, nutrient exchange, and other distinct metabolic responses. In these networks, microbial partners influence growth and N use efficiency of plants either positively or negatively. Harnessing the beneficial effects of specific players within crop microbiomes is a promising strategy to counteract the emerging threats to human and planetary health due to the overuse of industrial N fertilizers. However, in addition to N-providing activities (e.g. the well-known symbiosis of legumes and Rhizobium spp.), other plant-microorganism interactions must be considered to obtain a complete picture of how microbial-driven N transformations might affect plant nutrition. For this, we review recent insights into the tight interplay between plants and N-cycling microorganisms, focusing on microbial N-transformation processes representing N sources and sinks that ultimately shape plant N acquisition.
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Affiliation(s)
- Hanna Koch
- Center for Health & Bioresources, Bioresources Unit, AIT Austrian Institute of Technology GmbH, A-3430 Tulln, Austria
| | - Angela Sessitsch
- Center for Health & Bioresources, Bioresources Unit, AIT Austrian Institute of Technology GmbH, A-3430 Tulln, Austria
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4
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Rosales-Cruz A, Reyes-Nicolau J, Minto-González E, Meneses-Carbajal A, Mondragón-Albarrán C, López-Pliego L, Castañeda M. A Homolog of the Histidine Kinase RetS Controls the Synthesis of Alginates, PHB, Alkylresorcinols, and Motility in Azotobacter vinelandii. Curr Microbiol 2024; 81:311. [PMID: 39153035 PMCID: PMC11330419 DOI: 10.1007/s00284-024-03835-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2024] [Accepted: 08/08/2024] [Indexed: 08/19/2024]
Abstract
The two-component system GacS/A and the posttranscriptional control system Rsm constitute a genetic regulation pathway in Gammaproteobacteria; in some species of Pseudomonas, this pathway is part of a multikinase network (MKN) that regulates the activity of the Rsm system. In this network, the activity of GacS is controlled by other kinases. One of the most studied MKNs is the MKN-GacS of Pseudomonas aeruginosa, where GacS is controlled by the kinases RetS and LadS; RetS decreases the kinase activity of GacS, whereas LadS stimulates the activity of the central kinase GacS. Outside of the Pseudomonas genus, the network has been studied only in Azotobacter vinelandii. In this work, we report the study of the RetS kinase of A. vinelandii; as expected, the phenotypes affected in gacS mutants, such as production of alginates, polyhydroxybutyrate, and alkylresorcinols and swimming motility, were also affected in retS mutants. Interestingly, our data indicated that RetS in A. vinelandii acts as a positive regulator of GacA activity. Consistent with this finding, mutation in retS also negatively affected the expression of small regulatory RNAs belonging to the Rsm family. We also confirmed the interaction of RetS with GacS, as well as with the phosphotransfer protein HptB.
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Affiliation(s)
- Araceli Rosales-Cruz
- Centro de Investigaciones en Ciencias Microbiológicas, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, IC-11 Ciudad Universitaria Puebla, Apdo. Postal 1622, C. P. 72000, Puebla, Pue, Mexico
| | - Jimena Reyes-Nicolau
- Centro de Investigaciones en Ciencias Microbiológicas, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, IC-11 Ciudad Universitaria Puebla, Apdo. Postal 1622, C. P. 72000, Puebla, Pue, Mexico
| | - Eduardo Minto-González
- Centro de Investigaciones en Ciencias Microbiológicas, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, IC-11 Ciudad Universitaria Puebla, Apdo. Postal 1622, C. P. 72000, Puebla, Pue, Mexico
| | - Alan Meneses-Carbajal
- Centro de Investigaciones en Ciencias Microbiológicas, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, IC-11 Ciudad Universitaria Puebla, Apdo. Postal 1622, C. P. 72000, Puebla, Pue, Mexico
| | - Claudia Mondragón-Albarrán
- Centro de Investigaciones en Ciencias Microbiológicas, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, IC-11 Ciudad Universitaria Puebla, Apdo. Postal 1622, C. P. 72000, Puebla, Pue, Mexico
| | - Liliana López-Pliego
- Centro de Investigaciones en Ciencias Microbiológicas, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, IC-11 Ciudad Universitaria Puebla, Apdo. Postal 1622, C. P. 72000, Puebla, Pue, Mexico
| | - Miguel Castañeda
- Centro de Investigaciones en Ciencias Microbiológicas, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, IC-11 Ciudad Universitaria Puebla, Apdo. Postal 1622, C. P. 72000, Puebla, Pue, Mexico.
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5
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Rose SA, Robicheau BM, Tolman J, Fonseca-Batista D, Rowland E, Desai D, Ratten JM, Kantor EJH, Comeau AM, Langille MG, Jerlström-Hultqvist J, Devred E, Sarthou G, Bertrand EM, LaRoche J. Nitrogen fixation in the widely distributed marine γ-proteobacterial diazotroph Candidatus Thalassolituus haligoni. SCIENCE ADVANCES 2024; 10:eadn1476. [PMID: 39083619 PMCID: PMC11290528 DOI: 10.1126/sciadv.adn1476] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2023] [Accepted: 06/25/2024] [Indexed: 08/02/2024]
Abstract
The high diversity and global distribution of heterotrophic bacterial diazotrophs (HBDs) in the ocean has recently become apparent. However, understanding the role these largely uncultured microorganisms play in marine N2 fixation poses a challenge due to their undefined growth requirements and the complex regulation of the nitrogenase enzyme. We isolated and characterized Candidatus Thalassolituus haligoni, a member of a widely distributed clade of HBD belonging to the Oceanospirillales. Analysis of its nifH gene via amplicon sequencing revealed the extensive distribution of Cand. T. haligoni across the Pacific, Atlantic, and Arctic Oceans. Pangenome analysis indicates that the isolate shares >99% identity with an uncultured metagenome-assembled genome called Arc-Gamma-03, recently recovered from the Arctic Ocean. Through combined genomic, proteomic, and physiological approaches, we confirmed that the isolate fixes N2 gas. However, the mechanisms governing nitrogenase regulation in Cand. T. haligoni remain unclear. We propose Cand. T. haligoni as a globally distributed, cultured HBD model species within this understudied clade of Oceanospirillales.
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Affiliation(s)
- Sonja A. Rose
- Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Brent M. Robicheau
- Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Jennifer Tolman
- Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Debany Fonseca-Batista
- Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada
- Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Elden Rowland
- Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Dhwani Desai
- Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada
- Integrated Microbiome Resource (IMR) and Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Jenni-Marie Ratten
- Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Ella Joy H. Kantor
- Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - André M. Comeau
- Integrated Microbiome Resource (IMR) and Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Morgan G.I. Langille
- Integrated Microbiome Resource (IMR) and Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia, Canada
| | | | - Emmanuel Devred
- Fisheries and Oceans Canada, Bedford Institute of Oceanography, Halifax, Nova Scotia, Canada
| | | | - Erin M. Bertrand
- Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Julie LaRoche
- Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada
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6
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Zhang L, Einsle O. Architecture of the RNF1 complex that drives biological nitrogen fixation. Nat Chem Biol 2024; 20:1078-1085. [PMID: 38890433 DOI: 10.1038/s41589-024-01641-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2022] [Accepted: 05/10/2024] [Indexed: 06/20/2024]
Abstract
Biological nitrogen fixation requires substantial metabolic energy in form of ATP as well as low-potential electrons that must derive from central metabolism. During aerobic growth, the free-living soil diazotroph Azotobacter vinelandii transfers electrons from the key metabolite NADH to the low-potential ferredoxin FdxA that serves as a direct electron donor to the dinitrogenase reductases. This process is mediated by the RNF complex that exploits the proton motive force over the cytoplasmic membrane to lower the midpoint potential of the transferred electron. Here we report the cryogenic electron microscopy structure of the nitrogenase-associated RNF complex of A. vinelandii, a seven-subunit membrane protein assembly that contains four flavin cofactors and six iron-sulfur centers. Its function requires the strict coupling of electron and proton transfer but also involves major conformational changes within the assembly that can be traced with a combination of electron microscopy and modeling.
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Affiliation(s)
- Lin Zhang
- Institut für Biochemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Oliver Einsle
- Institut für Biochemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany.
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7
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Barney BM, Dietz BR. Precision control of ammonium release in Azotobacter vinelandii. Microb Biotechnol 2024; 17:e14523. [PMID: 39023513 PMCID: PMC11256883 DOI: 10.1111/1751-7915.14523] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2024] [Accepted: 06/27/2024] [Indexed: 07/20/2024] Open
Abstract
The capture and reduction of atmospheric dinitrogen gas to ammonium can be accomplished through the enzyme nitrogenase in a process known as biological nitrogen fixation (BNF), by a class of microbes known as diazotrophs. The diazotroph Azotobacter vinelandii is a model organism for the study of aerobic nitrogen fixation, and in recent years has been promoted as a potential producer of biofertilizers. Prior reports have demonstrated the potential to partially deregulate BNF in A. vinelandii, resulting in accumulation and extracellular release of ammonium. In many cases, deregulation requires the introduction of transgenic genes or elements to yield the desired phenotype, and the long-term stability of these strains has been reported to be somewhat problematic. In this work, we constructed two strains of A. vinelandii where regulation can be precisely controlled without the addition of any foreign genes or genetic markers. Regulation is maintained through native promoters found in A. vinelandii that can be induced through the addition of extraneous galactose. These strains result in varied degrees of regulation of BNF, and as a result, the release of extracellular ammonium is controlled in a precise, and galactose concentration-dependent manner. In addition, these strains yield high biomass levels, similar to the wild-type A. vinelandii strain and are further able to produce high percentages of the bioplastic polyhydroxybutyrate.
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Affiliation(s)
- Brett M. Barney
- Department of Bioproducts and Biosystems EngineeringUniversity of MinnesotaSt. PaulMinnesotaUSA
- Biotechnology InstituteUniversity of MinnesotaSt. PaulMinnesotaUSA
| | - Benjamin R. Dietz
- Department of Bioproducts and Biosystems EngineeringUniversity of MinnesotaSt. PaulMinnesotaUSA
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8
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Ambrosio R, Burgos Herrera G, Do Nascimento M, Pagnussat LA, Curatti L. Competitive fitness and stability of ammonium-excreting Azotobacter vinelandii strains in the soil. Appl Microbiol Biotechnol 2024; 108:378. [PMID: 38888816 PMCID: PMC11189346 DOI: 10.1007/s00253-024-13231-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2024] [Revised: 06/03/2024] [Accepted: 06/08/2024] [Indexed: 06/20/2024]
Abstract
Non-symbiotic N2-fixation would greatly increase the versatility of N-biofertilizers for sustainable agriculture. Genetic modification of diazotrophic bacteria has successfully enhanced NH4+ release. In this study, we compared the competitive fitness of A. vinelandii mutant strains, which allowed us to analyze the burden of NH4+ release under a broad dynamic range. Long-term competition assays under regular culture conditions confirmed a large burden for NH4+ release, exclusion by the wt strain, phenotypic instability, and loss of the ability to release NH4+. In contrast, co-inoculation in mild autoclaved soil showed a much longer co-existence with the wt strain and a stable NH4+ release phenotype. All genetically modified strains increased the N content and changed its chemical speciation in the soil. This study contributes one step forward towards bridging a knowledge gap between molecular biology laboratory research and the incorporation of N from the air into the soil in a molecular species suitable for plant nutrition, a crucial requirement for developing improved bacterial inoculants for economic and environmentally sustainable agriculture. KEY POINTS: • Genetic engineering for NH4+ excretion imposes a fitness burden on the culture medium • Large phenotypic instability for NH4+-excreting bacteria in culture medium • Lower fitness burden and phenotypic instability for NH4+-excreting bacteria in soil.
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Affiliation(s)
- Rafael Ambrosio
- Instituto de Investigaciones en Biodiversidad y Biotecnología (INBIOTEC), Consejo Nacional de Investigaciones Científicas y Técnicas, Vieytes 3103, 7600, Mar del PlataBuenos Aires, Argentina
- Fundación para Investigaciones Biológicas Aplicadas, Mar del Plata, Buenos Aires, Argentina
- Instituto de Agrobiotecnología del Litoral, Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad Nacional del Litoral, Santa Fe, Santa Fe, Argentina
| | - Gonzalo Burgos Herrera
- Instituto de Investigaciones en Biodiversidad y Biotecnología (INBIOTEC), Consejo Nacional de Investigaciones Científicas y Técnicas, Vieytes 3103, 7600, Mar del PlataBuenos Aires, Argentina
- Fundación para Investigaciones Biológicas Aplicadas, Mar del Plata, Buenos Aires, Argentina
| | - Mauro Do Nascimento
- Instituto de Investigaciones en Biodiversidad y Biotecnología (INBIOTEC), Consejo Nacional de Investigaciones Científicas y Técnicas, Vieytes 3103, 7600, Mar del PlataBuenos Aires, Argentina
- Fundación para Investigaciones Biológicas Aplicadas, Mar del Plata, Buenos Aires, Argentina
| | - Luciana Anabella Pagnussat
- Instituto de Investigaciones en Biodiversidad y Biotecnología (INBIOTEC), Consejo Nacional de Investigaciones Científicas y Técnicas, Vieytes 3103, 7600, Mar del PlataBuenos Aires, Argentina
- Fundación para Investigaciones Biológicas Aplicadas, Mar del Plata, Buenos Aires, Argentina
- Facultad de Ciencias Agrarias, Universidad Nacional de Mar del Plata, Balcarce, Buenos Aires, Argentina
| | - Leonardo Curatti
- Instituto de Investigaciones en Biodiversidad y Biotecnología (INBIOTEC), Consejo Nacional de Investigaciones Científicas y Técnicas, Vieytes 3103, 7600, Mar del PlataBuenos Aires, Argentina.
- Fundación para Investigaciones Biológicas Aplicadas, Mar del Plata, Buenos Aires, Argentina.
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9
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Shomar H, Bokinsky G. Harnessing iron‑sulfur enzymes for synthetic biology. BIOCHIMICA ET BIOPHYSICA ACTA. MOLECULAR CELL RESEARCH 2024; 1871:119718. [PMID: 38574823 DOI: 10.1016/j.bbamcr.2024.119718] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2024] [Revised: 03/13/2024] [Accepted: 03/25/2024] [Indexed: 04/06/2024]
Abstract
Reactions catalysed by iron-sulfur (Fe-S) enzymes appear in a variety of biosynthetic pathways that produce valuable natural products. Harnessing these biosynthetic pathways by expression in microbial cell factories grown on an industrial scale would yield enormous economic and environmental benefits. However, Fe-S enzymes often become bottlenecks that limits the productivity of engineered pathways. As a consequence, achieving the production metrics required for industrial application remains a distant goal for Fe-S enzyme-dependent pathways. Here, we identify and review three core challenges in harnessing Fe-S enzyme activity, which all stem from the properties of Fe-S clusters: 1) limited Fe-S cluster supply within the host cell, 2) Fe-S cluster instability, and 3) lack of specialized reducing cofactor proteins often required for Fe-S enzyme activity, such as enzyme-specific flavodoxins and ferredoxins. We highlight successful methods developed for a variety of Fe-S enzymes and electron carriers for overcoming these difficulties. We use heterologous nitrogenase expression as a grand case study demonstrating how each of these challenges can be addressed. We predict that recent breakthroughs in protein structure prediction and design will prove well-suited to addressing each of these challenges. A reliable toolkit for harnessing Fe-S enzymes in engineered metabolic pathways will accelerate the development of industry-ready Fe-S enzyme-dependent biosynthesis pathways.
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Affiliation(s)
- Helena Shomar
- Institut Pasteur, université Paris Cité, Inserm U1284, Diversité moléculaire des microbes (Molecular Diversity of Microbes lab), 75015 Paris, France
| | - Gregory Bokinsky
- Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Delft, the Netherlands.
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10
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Addison H, Glatter T, K. A. Hochberg G, Rebelein JG. Two distinct ferredoxins are essential for nitrogen fixation by the iron nitrogenase in Rhodobacter capsulatus. mBio 2024; 15:e0331423. [PMID: 38377621 PMCID: PMC10936413 DOI: 10.1128/mbio.03314-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2023] [Accepted: 01/29/2024] [Indexed: 02/22/2024] Open
Abstract
Nitrogenases are the only enzymes able to fix gaseous nitrogen into bioavailable ammonia and hence are essential for sustaining life. Catalysis by nitrogenases requires both a large amount of ATP and electrons donated by strongly reducing ferredoxins or flavodoxins. Our knowledge about the mechanisms of electron transfer to nitrogenase enzymes is limited: The electron transport to the iron (Fe)-nitrogenase has hardly been investigated. Here, we characterized the electron transfer pathway to the Fe-nitrogenase in Rhodobacter capsulatus via proteome analyses, genetic deletions, complementation studies, and phylogenetics. Proteome analyses revealed an upregulation of four ferredoxins under nitrogen-fixing conditions reliant on the Fe-nitrogenase in a molybdenum nitrogenase knockout strain, compared to non-nitrogen-fixing conditions. Based on these findings, R. capsulatus strains with deletions of ferredoxin (fdx) and flavodoxin (fld, nifF) genes were constructed to investigate their roles in nitrogen fixation by the Fe-nitrogenase. R. capsulatus deletion strains were characterized by monitoring diazotrophic growth and Fe-nitrogenase activity in vivo. Only deletions of fdxC or fdxN resulted in slower growth and reduced Fe-nitrogenase activity, whereas the double deletion of both fdxC and fdxN abolished diazotrophic growth. Differences in the proteomes of ∆fdxC and ∆fdxN strains, in conjunction with differing plasmid complementation behaviors of fdxC and fdxN, indicate that the two Fds likely possess different roles and functions. These findings will guide future engineering of the electron transport systems to nitrogenase enzymes, with the aim of increased electron flux and product formation.IMPORTANCENitrogenases are essential for biological nitrogen fixation, converting atmospheric nitrogen gas to bioavailable ammonia. The production of ammonia by diazotrophic organisms, harboring nitrogenases, is essential for sustaining plant growth. Hence, there is a large scientific interest in understanding the cellular mechanisms for nitrogen fixation via nitrogenases. Nitrogenases rely on highly reduced electrons to power catalysis, although we lack knowledge as to which proteins shuttle the electrons to nitrogenases within cells. Here, we characterized the electron transport to the iron (Fe)-nitrogenase in the model diazotroph Rhodobacter capsulatus, showing that two distinct ferredoxins are very important for nitrogen fixation despite having different redox centers. In addition, our research expands upon the debate on whether ferredoxins have functional redundancy or perform distinct roles within cells. Here, we observe that both essential ferredoxins likely have distinct roles based on differential proteome shifts of deletion strains and different complementation behaviors.
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Affiliation(s)
- Holly Addison
- Microbial Metalloenzymes Research Group, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Timo Glatter
- Core Facility for Mass Spectrometry & Proteomics, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Georg K. A. Hochberg
- Evolutionary Biochemistry Research Group, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
- Center for Synthetic Microbiology (SYNMIKRO), Philipps University Marburg, Marburg, Germany
| | - Johannes G. Rebelein
- Microbial Metalloenzymes Research Group, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
- Center for Synthetic Microbiology (SYNMIKRO), Philipps University Marburg, Marburg, Germany
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11
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Dietz BR, Olszewski NE, Barney BM. Enhanced extracellular ammonium release in the plant endophyte Gluconacetobacter diazotrophicus through genome editing. Microbiol Spectr 2024; 12:e0247823. [PMID: 38038458 PMCID: PMC10783055 DOI: 10.1128/spectrum.02478-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2023] [Accepted: 10/27/2023] [Indexed: 12/02/2023] Open
Abstract
IMPORTANCE Our results demonstrate increased extracellular ammonium release in the endophyte plant growth-promoting bacterium Gluconacetobacter diazotrophicus. Strains were constructed in a manner that leaves no antibiotic markers behind, such that these strains contain no transgenes. Levels of ammonium achieved by cultures of modified G. diazotrophicus strains reached concentrations of approximately 18 mM ammonium, while wild-type G. diazotrophicus remained much lower (below 50 µM). These findings demonstrate a strong potential for further improving the biofertilizer potential of this important microbe.
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Affiliation(s)
- Benjamin R. Dietz
- Department of Bioproducts and Biosystems Engineering, University of Minnesota, St. Paul, Minnesota, USA
| | - Neil E. Olszewski
- Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA
| | - Brett M. Barney
- Department of Bioproducts and Biosystems Engineering, University of Minnesota, St. Paul, Minnesota, USA
- Biotechnology Institute, University of Minnesota, St. Paul, Minnesota, USA
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12
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Sher AW, Aufrecht JA, Herrera D, Zimmerman AE, Kim YM, Munoz N, Trejo JB, Paurus VL, Cliff JB, Hu D, Chrisler WB, Tournay RJ, Gomez-Rivas E, Orr G, Ahkami AH, Doty SL. Dynamic nitrogen fixation in an aerobic endophyte of Populus. THE ISME JOURNAL 2024; 18:wrad012. [PMID: 38365250 PMCID: PMC10833079 DOI: 10.1093/ismejo/wrad012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2023] [Revised: 11/11/2023] [Accepted: 11/21/2023] [Indexed: 02/18/2024]
Abstract
Biological nitrogen fixation by microbial diazotrophs can contribute significantly to nitrogen availability in non-nodulating plant species. In this study of molecular mechanisms and gene expression relating to biological nitrogen fixation, the aerobic nitrogen-fixing endophyte Burkholderia vietnamiensis, strain WPB, isolated from Populus trichocarpa served as a model for endophyte-poplar interactions. Nitrogen-fixing activity was observed to be dynamic on nitrogen-free medium with a subset of colonies growing to form robust, raised globular like structures. Secondary ion mass spectrometry (NanoSIMS) confirmed that N-fixation was uneven within the population. A fluorescent transcriptional reporter (GFP) revealed that the nitrogenase subunit nifH is not uniformly expressed across genetically identical colonies of WPB and that only ~11% of the population was actively expressing the nifH gene. Higher nifH gene expression was observed in clustered cells through monitoring individual bacterial cells using single-molecule fluorescence in situ hybridization. Through 15N2 enrichment, we identified key nitrogenous metabolites and proteins synthesized by WPB and employed targeted metabolomics in active and inactive populations. We cocultivated WPB Pnif-GFP with poplar within a RhizoChip, a synthetic soil habitat, which enabled direct imaging of microbial nifH expression within root epidermal cells. We observed that nifH expression is localized to the root elongation zone where the strain forms a unique physical interaction with the root cells. This work employed comprehensive experimentation to identify novel mechanisms regulating both biological nitrogen fixation and beneficial plant-endophyte interactions.
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Affiliation(s)
- Andrew W Sher
- School of Environmental and Forest Sciences, College of the Environment, University of Washington, Seattle, WA, 98195-2100, United States
| | - Jayde A Aufrecht
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99354, United States
| | - Daisy Herrera
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99354, United States
| | - Amy E Zimmerman
- Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA, 99354, United States
| | - Young-Mo Kim
- Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA, 99354, United States
| | - Nathalie Munoz
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99354, United States
| | - Jesse B Trejo
- Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA, 99354, United States
| | - Vanessa L Paurus
- Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA, 99354, United States
| | - John B Cliff
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99354, United States
| | - Dehong Hu
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99354, United States
| | - William B Chrisler
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99354, United States
| | - Robert J Tournay
- School of Environmental and Forest Sciences, College of the Environment, University of Washington, Seattle, WA, 98195-2100, United States
| | - Emma Gomez-Rivas
- School of Environmental and Forest Sciences, College of the Environment, University of Washington, Seattle, WA, 98195-2100, United States
| | - Galya Orr
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99354, United States
| | - Amir H Ahkami
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99354, United States
| | - Sharon L Doty
- School of Environmental and Forest Sciences, College of the Environment, University of Washington, Seattle, WA, 98195-2100, United States
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13
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Einsle O. On the Shoulders of Giants-Reaching for Nitrogenase. Molecules 2023; 28:7959. [PMID: 38138449 PMCID: PMC10745432 DOI: 10.3390/molecules28247959] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2023] [Revised: 11/14/2023] [Accepted: 11/27/2023] [Indexed: 12/24/2023] Open
Abstract
Only a single enzyme system-nitrogenase-carries out the conversion of atmospheric N2 into bioavailable ammonium, an essential prerequisite for all organismic life. The reduction of this inert substrate at ambient conditions poses unique catalytic challenges that strain our mechanistic understanding even after decades of intense research. Structural biology has added its part to this greater tapestry, and in this review, I provide a personal (and highly biased) summary of the parts of the story to which I had the privilege to contribute. It focuses on the crystallographic analysis of the three isoforms of nitrogenases at high resolution and the binding of ligands and inhibitors to the active-site cofactors of the enzyme. In conjunction with the wealth of available biochemical, biophysical, and spectroscopic data on the protein, this has led us to a mechanistic hypothesis based on an elementary mechanism of repetitive hydride formation and insertion.
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Affiliation(s)
- Oliver Einsle
- Institute of Biochemistry, Albert-Ludwigs-Universität Freiburg, Albertstrasse 21, 79104 Freiburg im Breisgau, Germany
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14
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Einsle O. Catalysis and structure of nitrogenases. Curr Opin Struct Biol 2023; 83:102719. [PMID: 37802004 DOI: 10.1016/j.sbi.2023.102719] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2023] [Revised: 09/03/2023] [Accepted: 09/06/2023] [Indexed: 10/08/2023]
Abstract
In providing bioavailable nitrogen as building blocks for all classes of biomacromolecules, biological nitrogen fixation is an essential process for all organismic life. Only a single enzyme, nitrogenase, performs this task at ambient conditions and with ATP as an energy source. The assembly of the complex iron-sulfur enzyme nitrogenase and its catalytic mechanism remains a matter of intense study. Recent progress in the structural analysis of the three known isoforms of nitrogenase-differentiated primarily by the heterometal in their active site cofactor-has revealed a degree of structural plasticity of these clusters that suggest two distinct binding sites for substrates and reaction intermediates. A mechanistic proposal based on this finding integrates most of the available experimental data. Furthermore, the first applications of high-resolution cryo-electron microscopy have highlighted further dynamic conformational changes. Structures obtained under turnover conditions support the proposed alternating half-site reactivity in the C2-symmetric nitrogenase complex.
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Affiliation(s)
- Oliver Einsle
- Institut für Biochemie, Albert-Ludwigs-Universität Freiburg, Albertstrasse 21, 79104 Freiburg im Breisgau, Germany.
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15
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Barreras-Urbina C, Rodríguez-Félix F, Cárdenas-López JL, Plascencia-Jatomea M, Pérez-Tello M, Ledesma-Osuna AI, Madera-Santana TJ, Tapia-Hernández JA, Castro-Enríquez DD. Effect of a Prolonged-Release System of Urea on Nitrogen Losses and Microbial Population Changes in Two Types of Agricultural Soil. ACS OMEGA 2023; 8:42319-42328. [PMID: 38024718 PMCID: PMC10652818 DOI: 10.1021/acsomega.3c04572] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/26/2023] [Revised: 10/10/2023] [Accepted: 10/13/2023] [Indexed: 12/01/2023]
Abstract
Urea is the nitrogen-containing fertilizer most used in agricultural fields; however, the nutrient given by the urea is lost into the environment. The aim of this research was to determine the effect of two soil textures by applying a prolonged-release system of urea (PRSU) on the N losses. This research shows an important decrease of the nitrate and ammonium losses from 24.91 to 87.94%. Also, the microbiological population increases after the application of the PRSU. It was concluded that both soil textures presented the same loss-reduction pattern, where the N from the nitrates and ammonium was reduced in the leachates, increasing the quality of the soil and the microbial population in both soil textures after the PRSU application.
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Affiliation(s)
- Carlos
Gregorio Barreras-Urbina
- Departamento
de Investigación y Posgrado en Alimentos (DIPA), Universidad de Sonora, Hermosillo, Sonora 83000 Mexico
- Centro
de Investigación en Alimentación y Desarrollo, A. C., Coordinación de Tecnología de Alimentos
de Origen Vegetal, Carretera
Gustavo Enrique Astiazarán Rosas Núm. 46. La Victoria, C.P., 83304 Hermosillo, Sonora México
| | - Francisco Rodríguez-Félix
- Departamento
de Investigación y Posgrado en Alimentos (DIPA), Universidad de Sonora, Hermosillo, Sonora 83000 Mexico
| | - José Luis Cárdenas-López
- Departamento
de Investigación y Posgrado en Alimentos (DIPA), Universidad de Sonora, Hermosillo, Sonora 83000 Mexico
| | - Maribel Plascencia-Jatomea
- Departamento
de Investigación y Posgrado en Alimentos (DIPA), Universidad de Sonora, Hermosillo, Sonora 83000 Mexico
| | - Manuel Pérez-Tello
- Departamento
de Ingeniería Química y Metalurgia, Universidad de Sonora, Hermosillo, Sonora 83000 Mexico
| | - Ana Irene Ledesma-Osuna
- Departamento
de Investigación y Posgrado en Alimentos (DIPA), Universidad de Sonora, Hermosillo, Sonora 83000 Mexico
| | - Tomás Jesús Madera-Santana
- Centro
de Investigación en Alimentación y Desarrollo, A. C., Coordinación de Tecnología de Alimentos
de Origen Vegetal, Carretera
Gustavo Enrique Astiazarán Rosas Núm. 46. La Victoria, C.P., 83304 Hermosillo, Sonora México
| | - José Agustín Tapia-Hernández
- Departamento
de Investigación y Posgrado en Alimentos (DIPA), Universidad de Sonora, Hermosillo, Sonora 83000 Mexico
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16
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Rosa-Núñez E, Echavarri-Erasun C, Armas AM, Escudero V, Poza-Carrión C, Rubio LM, González-Guerrero M. Iron Homeostasis in Azotobacter vinelandii. BIOLOGY 2023; 12:1423. [PMID: 37998022 PMCID: PMC10669500 DOI: 10.3390/biology12111423] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2023] [Revised: 11/07/2023] [Accepted: 11/10/2023] [Indexed: 11/25/2023]
Abstract
Iron is an essential nutrient for all life forms. Specialized mechanisms exist in bacteria to ensure iron uptake and its delivery to key enzymes within the cell, while preventing toxicity. Iron uptake and exchange networks must adapt to the different environmental conditions, particularly those that require the biosynthesis of multiple iron proteins, such as nitrogen fixation. In this review, we outline the mechanisms that the model diazotrophic bacterium Azotobacter vinelandii uses to ensure iron nutrition and how it adapts Fe metabolism to diazotrophic growth.
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Affiliation(s)
- Elena Rosa-Núñez
- Centro de Biotecnología y Genómica de Plantas (UPM-INIA/CSIC), Campus de Montegancedo UPM, Crta. M-40 km 38, 28223 Madrid, Spain; (E.R.-N.); (C.E.-E.); (A.M.A.); (C.P.-C.); (L.M.R.)
- Escuela Técnica de Ingeniería Agraria, Alimentaria, y de Biosistemas, Universidad Politécnica de Madrid, Avda. Puerta de Hierro, 2, 28040 Madrid, Spain
| | - Carlos Echavarri-Erasun
- Centro de Biotecnología y Genómica de Plantas (UPM-INIA/CSIC), Campus de Montegancedo UPM, Crta. M-40 km 38, 28223 Madrid, Spain; (E.R.-N.); (C.E.-E.); (A.M.A.); (C.P.-C.); (L.M.R.)
- Escuela Técnica de Ingeniería Agraria, Alimentaria, y de Biosistemas, Universidad Politécnica de Madrid, Avda. Puerta de Hierro, 2, 28040 Madrid, Spain
| | - Alejandro M. Armas
- Centro de Biotecnología y Genómica de Plantas (UPM-INIA/CSIC), Campus de Montegancedo UPM, Crta. M-40 km 38, 28223 Madrid, Spain; (E.R.-N.); (C.E.-E.); (A.M.A.); (C.P.-C.); (L.M.R.)
| | - Viviana Escudero
- Centro de Biotecnología y Genómica de Plantas (UPM-INIA/CSIC), Campus de Montegancedo UPM, Crta. M-40 km 38, 28223 Madrid, Spain; (E.R.-N.); (C.E.-E.); (A.M.A.); (C.P.-C.); (L.M.R.)
| | - César Poza-Carrión
- Centro de Biotecnología y Genómica de Plantas (UPM-INIA/CSIC), Campus de Montegancedo UPM, Crta. M-40 km 38, 28223 Madrid, Spain; (E.R.-N.); (C.E.-E.); (A.M.A.); (C.P.-C.); (L.M.R.)
| | - Luis M. Rubio
- Centro de Biotecnología y Genómica de Plantas (UPM-INIA/CSIC), Campus de Montegancedo UPM, Crta. M-40 km 38, 28223 Madrid, Spain; (E.R.-N.); (C.E.-E.); (A.M.A.); (C.P.-C.); (L.M.R.)
| | - Manuel González-Guerrero
- Centro de Biotecnología y Genómica de Plantas (UPM-INIA/CSIC), Campus de Montegancedo UPM, Crta. M-40 km 38, 28223 Madrid, Spain; (E.R.-N.); (C.E.-E.); (A.M.A.); (C.P.-C.); (L.M.R.)
- Escuela Técnica de Ingeniería Agraria, Alimentaria, y de Biosistemas, Universidad Politécnica de Madrid, Avda. Puerta de Hierro, 2, 28040 Madrid, Spain
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17
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Zayed O, Hewedy OA, Abdelmoteleb A, Ali M, Youssef MS, Roumia AF, Seymour D, Yuan ZC. Nitrogen Journey in Plants: From Uptake to Metabolism, Stress Response, and Microbe Interaction. Biomolecules 2023; 13:1443. [PMID: 37892125 PMCID: PMC10605003 DOI: 10.3390/biom13101443] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Revised: 09/19/2023] [Accepted: 09/19/2023] [Indexed: 10/29/2023] Open
Abstract
Plants uptake and assimilate nitrogen from the soil in the form of nitrate, ammonium ions, and available amino acids from organic sources. Plant nitrate and ammonium transporters are responsible for nitrate and ammonium translocation from the soil into the roots. The unique structure of these transporters determines the specificity of each transporter, and structural analyses reveal the mechanisms by which these transporters function. Following absorption, the nitrogen metabolism pathway incorporates the nitrogen into organic compounds via glutamine synthetase and glutamate synthase that convert ammonium ions into glutamine and glutamate. Different isoforms of glutamine synthetase and glutamate synthase exist, enabling plants to fine-tune nitrogen metabolism based on environmental cues. Under stressful conditions, nitric oxide has been found to enhance plant survival under drought stress. Furthermore, the interaction between salinity stress and nitrogen availability in plants has been studied, with nitric oxide identified as a potential mediator of responses to salt stress. Conversely, excessive use of nitrate fertilizers can lead to health and environmental issues. Therefore, alternative strategies, such as establishing nitrogen fixation in plants through diazotrophic microbiota, have been explored to reduce reliance on synthetic fertilizers. Ultimately, genomics can identify new genes related to nitrogen fixation, which could be harnessed to improve plant productivity.
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Affiliation(s)
- Omar Zayed
- Department of Botany and Plant Sciences, University of California Riverside, Riverside, CA 9250, USA;
- Genetics Department, Faculty of Agriculture, Menoufia University, Shebin El-Kom 32511, Egypt;
| | - Omar A. Hewedy
- Genetics Department, Faculty of Agriculture, Menoufia University, Shebin El-Kom 32511, Egypt;
- Department of Plant Agriculture, University of Guelph, 50 Stone Road East, Guelph, ON N1G 2W1, Canada
| | - Ali Abdelmoteleb
- Botany Department, Faculty of Agriculture, Menoufia University, Shebin El-Kom 32511, Egypt;
| | - Mohammed Ali
- Maryout Research Station, Genetic Resources Department, Desert Research Center, 1 Mathaf El-Matarya St., El-Matareya, Cairo 11753, Egypt;
| | - Mohamed S. Youssef
- Botany and Microbiology Department, Faculty of Science, Kafrelsheikh University, Kafrelsheikh 33516, Egypt;
- Department of Plant Science, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
| | - Ahmed F. Roumia
- Department of Agricultural Biochemistry, Faculty of Agriculture, Menoufia University, Shibin El-Kom 32514, Egypt;
| | - Danelle Seymour
- Department of Botany and Plant Sciences, University of California Riverside, Riverside, CA 9250, USA;
| | - Ze-Chun Yuan
- Agriculture and Agri-Food Canada, 1391 Sandford Street, London, ON N5V 4T3, Canada
- Department of Microbiology and Immunology, The University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B7, Canada
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18
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Rivier AJ, Myers KS, Garcia AK, Sobol MS, Kaçar B. Regulatory response to a hybrid ancestral nitrogenase in Azotobacter vinelandii. Microbiol Spectr 2023; 11:e0281523. [PMID: 37702481 PMCID: PMC10581106 DOI: 10.1128/spectrum.02815-23] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2023] [Accepted: 07/20/2023] [Indexed: 09/14/2023] Open
Abstract
Biological nitrogen fixation, the microbial reduction of atmospheric nitrogen to bioavailable ammonia, represents both a major limitation on biological productivity and a highly desirable engineering target for synthetic biology. However, the engineering of nitrogen fixation requires an integrated understanding of how the gene regulatory dynamics of host diazotrophs respond across sequence-function space of its central catalytic metalloenzyme, nitrogenase. Here, we interrogate this relationship by analyzing the transcriptome of Azotobacter vinelandii engineered with a phylogenetically inferred ancestral nitrogenase protein variant. The engineered strain exhibits reduced cellular nitrogenase activity but recovers wild-type growth rates following an extended lag period. We find that expression of genes within the immediate nitrogen fixation network is resilient to the introduced nitrogenase sequence-level perturbations. Rather the sustained physiological compatibility with the ancestral nitrogenase variant is accompanied by reduced expression of genes that support trace metal and electron resource allocation to nitrogenase. Our results spotlight gene expression changes in cellular processes adjacent to nitrogen fixation as productive engineering considerations to improve compatibility between remodeled nitrogenase proteins and engineered host diazotrophs. IMPORTANCE Azotobacter vinelandii is a key model bacterium for the study of biological nitrogen fixation, an important metabolic process catalyzed by nitrogenase enzymes. Here, we demonstrate that compatibilities between engineered A. vinelandii strains and nitrogenase variants can be modulated at the regulatory level. The engineered strain studied here responds by adjusting the expression of proteins involved in cellular processes adjacent to nitrogen fixation, rather than that of nitrogenase proteins themselves. These insights can inform future strategies to transfer nitrogenase variants to non-native hosts.
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Affiliation(s)
- Alex J. Rivier
- Department of Bacteriology, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Kevin S. Myers
- Great Lakes Bioenergy Research Center and the Wisconsin Energy Institute, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Amanda K. Garcia
- Department of Bacteriology, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Morgan S. Sobol
- Department of Bacteriology, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Betül Kaçar
- Department of Bacteriology, University of Wisconsin-Madison, Madison, Wisconsin, USA
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19
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Ikeda S, Tomita K, Nakagawa G, Kouzuma A, Watanabe K. Supplementation with Amino Acid Sources Facilitates Fermentative Growth of Shewanella oneidensis MR-1 in Defined Media. Appl Environ Microbiol 2023; 89:e0086823. [PMID: 37367298 PMCID: PMC10370299 DOI: 10.1128/aem.00868-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2023] [Accepted: 06/04/2023] [Indexed: 06/28/2023] Open
Abstract
Shewanella oneidensis MR-1 is a facultative anaerobe that grows by respiration using a variety of electron acceptors. This organism serves as a model to study how bacteria thrive in redox-stratified environments. A glucose-utilizing engineered derivative of MR-1 has been reported to be unable to grow in glucose minimal medium (GMM) in the absence of electron acceptors, despite this strain having a complete set of genes for reconstructing glucose to lactate fermentative pathways. To gain insights into why MR-1 is incapable of fermentative growth, this study examined a hypothesis that this strain is programmed to repress the expression of some carbon metabolic genes in the absence of electron acceptors. Comparative transcriptomic analyses of the MR-1 derivative were conducted in the presence and absence of fumarate as an electron acceptor, and these found that the expression of many genes involved in carbon metabolism required for cell growth, including several tricarboxylic acid (TCA) cycle genes, was significantly downregulated in the absence of fumarate. This finding suggests a possibility that MR-1 is unable to grow fermentatively on glucose in minimal media owing to the shortage of nutrients essential for cell growth, such as amino acids. This idea was demonstrated in subsequent experiments that showed that the MR-1 derivative fermentatively grows in GMM containing tryptone or a defined mixture of amino acids. We suggest that gene regulatory circuits in MR-1 are tuned to minimize energy consumption under electron acceptor-depleted conditions, and that this results in defective fermentative growth in minimal media. IMPORTANCE It is an enigma why S. oneidensis MR-1 is incapable of fermentative growth despite having complete sets of genes for reconstructing fermentative pathways. Understanding the molecular mechanisms behind this defect will facilitate the development of novel fermentation technologies for the production of value-added chemicals from biomass feedstocks, such as electro-fermentation. The information provided in this study will also improve our understanding of the ecological strategies of bacteria living in redox-stratified environments.
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Affiliation(s)
- Sota Ikeda
- School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo, Japan
| | - Keisuke Tomita
- School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo, Japan
| | - Gen Nakagawa
- School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo, Japan
| | - Atsushi Kouzuma
- School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo, Japan
| | - Kazuya Watanabe
- School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo, Japan
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20
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Wang Z, Vishwanathan N, Kowaliczko S, Ishii S. Clarifying Microbial Nitrous Oxide Reduction under Aerobic Conditions: Tolerant, Intolerant, and Sensitive. Microbiol Spectr 2023; 11:e0470922. [PMID: 36926990 PMCID: PMC10100939 DOI: 10.1128/spectrum.04709-22] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2022] [Accepted: 02/18/2023] [Indexed: 03/17/2023] Open
Abstract
One of the major challenges for the bioremediation application of microbial nitrous oxide (N2O) reduction is its oxygen sensitivity. While a few strains were reported capable of reducing N2O under aerobic conditions, the N2O reduction kinetics of phylogenetically diverse N2O reducers are not well understood. Here, we analyzed and compared the kinetics of clade I and clade II N2O-reducing bacteria in the presence or absence of oxygen (O2) by using a whole-cell assay with N2O and O2 microsensors. Among the seven strains tested, N2O reduction of Stutzerimonas stutzeri TR2 and ZoBell was not inhibited by oxygen (i.e., oxygen tolerant). Paracoccus denitrificans, Azospirillum brasilense, and Gemmatimonas aurantiaca reduced N2O in the presence of O2 but slower than in the absence of O2 (i.e., oxygen sensitive). N2O reduction of Pseudomonas aeruginosa and Dechloromonas aromatica did not occur when O2 was present (i.e., oxygen intolerant). Amino acid sequences and predicted structures of NosZ were highly similar among these strains, whereas oxygen-tolerant N2O reducers had higher oxygen consumption rates. The results suggest that the mechanism of O2 tolerance is not directly related to NosZ structure but is rather related to the scavenging of O2 in the cells and/or accessory proteins encoded by the nos cluster. IMPORTANCE Some bacteria can reduce N2O in the presence of O2, whereas others cannot. It is unclear whether this trait of aerobic N2O reduction is related to the phylogeny and structure of N2O reductase. The understanding of aerobic N2O reduction is critical for guiding emission control, due to the common concurrence of N2O and O2 in natural and engineered systems. This study provided the N2O reduction kinetics of various bacteria under aerobic and anaerobic conditions and classified the bacteria into oxygen-tolerant, -sensitive, and -intolerant N2O reducers. Oxygen-tolerant N2O reducers rapidly consumed O2, which could help maintain the low O2 concentration in the cells and keep their N2O reductase active. These findings are important and useful when selecting N2O reducers for bioremediation applications.
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Affiliation(s)
- Zhiyue Wang
- Department of Civil and Environmental Engineering, University of Hawai'i, Honolulu, Hawai'i, USA
- Water Resources Research Center, University of Hawai'i, Honolulu, Hawai'i, USA
| | - Nisha Vishwanathan
- BioTechnology Institute, University of Minnesota, St. Paul, Minnesota, USA
| | - Sophie Kowaliczko
- BioTechnology Institute, University of Minnesota, St. Paul, Minnesota, USA
| | - Satoshi Ishii
- BioTechnology Institute, University of Minnesota, St. Paul, Minnesota, USA
- Department of Soil, Water, and Climate, University of Minnesota, St. Paul, Minnesota, USA
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21
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Martin Del Campo JS, Rigsbee J, Bueno Batista M, Mus F, Rubio LM, Einsle O, Peters JW, Dixon R, Dean DR, Dos Santos PC. Overview of physiological, biochemical, and regulatory aspects of nitrogen fixation in Azotobacter vinelandii. Crit Rev Biochem Mol Biol 2023; 57:492-538. [PMID: 36877487 DOI: 10.1080/10409238.2023.2181309] [Citation(s) in RCA: 12] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/07/2023]
Abstract
Understanding how Nature accomplishes the reduction of inert nitrogen gas to form metabolically tractable ammonia at ambient temperature and pressure has challenged scientists for more than a century. Such an understanding is a key aspect toward accomplishing the transfer of the genetic determinants of biological nitrogen fixation to crop plants as well as for the development of improved synthetic catalysts based on the biological mechanism. Over the past 30 years, the free-living nitrogen-fixing bacterium Azotobacter vinelandii emerged as a preferred model organism for mechanistic, structural, genetic, and physiological studies aimed at understanding biological nitrogen fixation. This review provides a contemporary overview of these studies and places them within the context of their historical development.
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Affiliation(s)
| | - Jack Rigsbee
- Department of Chemistry, Wake Forest University, Winston-Salem, NC, USA
| | | | - Florence Mus
- Institute of Biological Chemistry, Washington State University, Pullman, WA, USA
| | - Luis M Rubio
- Centro de Biotecnología y Genómica de Plantas, Universidad Politécnica de Madrid (UPM) - Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA/CSIC), Pozuelo de Alarcón, Spain
| | - Oliver Einsle
- Department of Biochemistry, University of Freiburg, Freiburg, Germany
| | - John W Peters
- Institute of Biological Chemistry, Washington State University, Pullman, WA, USA
| | - Ray Dixon
- Department of Molecular Microbiology, John Innes Centre, Norwich, UK
| | - Dennis R Dean
- Department of Biochemistry, Virginia Tech, Blacksburg, VA, USA
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22
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Lycus P, Einsle O, Zhang L. Structural biology of proteins involved in nitrogen cycling. Curr Opin Chem Biol 2023; 74:102278. [PMID: 36889028 DOI: 10.1016/j.cbpa.2023.102278] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2022] [Revised: 01/31/2023] [Accepted: 02/02/2023] [Indexed: 03/08/2023]
Abstract
Microbial metabolic processes drive the global nitrogen cycle through sophisticated and often unique metalloenzymes that facilitate difficult redox reactions at ambient temperature and pressure. Understanding the intricacies of these biological nitrogen transformations requires a detailed knowledge that arises from the combination of a multitude of powerful analytical techniques and functional assays. Recent developments in spectroscopy and structural biology have provided new, powerful tools for addressing existing and emerging questions, which have gained urgency due to the global environmental implications of these fundamental reactions. The present review focuses on the recent contributions of the wider area of structural biology to understanding nitrogen metabolism, opening new avenues for biotechnological applications to better manage and balance the challenges of the global nitrogen cycle.
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Affiliation(s)
- Pawel Lycus
- Institut für Biochemie, Albert-Ludwigs-Universität Freiburg, Albertstrasse 21, 79104, Freiburg im Breisgau, Germany; Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Ås, Norway
| | - Oliver Einsle
- Institut für Biochemie, Albert-Ludwigs-Universität Freiburg, Albertstrasse 21, 79104, Freiburg im Breisgau, Germany.
| | - Lin Zhang
- Institut für Biochemie, Albert-Ludwigs-Universität Freiburg, Albertstrasse 21, 79104, Freiburg im Breisgau, Germany.
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23
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Bennett EM, Murray JW, Isalan M. Engineering Nitrogenases for Synthetic Nitrogen Fixation: From Pathway Engineering to Directed Evolution. BIODESIGN RESEARCH 2023; 5:0005. [PMID: 37849466 PMCID: PMC10521693 DOI: 10.34133/bdr.0005] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2022] [Accepted: 12/24/2022] [Indexed: 10/19/2023] Open
Abstract
Globally, agriculture depends on industrial nitrogen fertilizer to improve crop growth. Fertilizer production consumes fossil fuels and contributes to environmental nitrogen pollution. A potential solution would be to harness nitrogenases-enzymes capable of converting atmospheric nitrogen N2 to NH3 in ambient conditions. It is therefore a major goal of synthetic biology to engineer functional nitrogenases into crop plants, or bacteria that form symbiotic relationships with crops, to support growth and reduce dependence on industrially produced fertilizer. This review paper highlights recent work toward understanding the functional requirements for nitrogenase expression and manipulating nitrogenase gene expression in heterologous hosts to improve activity and oxygen tolerance and potentially to engineer synthetic symbiotic relationships with plants.
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Affiliation(s)
- Emily M. Bennett
- Department of Life Sciences, Imperial College London, London SW7 2AZ, UK
| | - James W. Murray
- Department of Life Sciences, Imperial College London, London SW7 2AZ, UK
| | - Mark Isalan
- Department of Life Sciences, Imperial College London, London SW7 2AZ, UK
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24
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Gluconacetobacter diazotrophicus Gene Fitness during Diazotrophic Growth. Appl Environ Microbiol 2022; 88:e0124122. [PMID: 36374093 PMCID: PMC9746312 DOI: 10.1128/aem.01241-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Plant growth-promoting (PGP) bacteria are important to the development of sustainable agricultural systems. PGP microbes that fix atmospheric nitrogen (diazotrophs) could minimize the application of industrially derived fertilizers and function as a biofertilizer. The bacterium Gluconacetobacter diazotrophicus is a nitrogen-fixing PGP microbe originally discovered in association with sugarcane plants, where it functions as an endophyte. It also forms endophyte associations with a range of other agriculturally relevant crop plants. G. diazotrophicus requires microaerobic conditions for diazotrophic growth. We generated a transposon library for G. diazotrophicus and cultured the library under various growth conditions and culture medium compositions to measure fitness defects associated with individual transposon inserts (transposon insertion sequencing [Tn-seq]). Using this library, we probed more than 3,200 genes and ascertained the importance of various genes for diazotrophic growth of this microaerobic endophyte. We also identified a set of essential genes. IMPORTANCE Our results demonstrate a succinct set of genes involved in diazotrophic growth for G. diazotrophicus, with a lower degree of redundancy than what is found in other model diazotrophs. The results will serve as a valuable resource for those interested in biological nitrogen fixation and will establish a baseline data set for plant free growth, which could complement future studies related to the endophyte relationship.
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25
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Moreno S, Muriel-Millán LF, Rodríguez-Martínez K, Ortíz-Vasco C, Bedoya-Pérez LP, Espín G. The ribosome rescue pathways SsrA-SmpB, ArfA, and ArfB mediate tolerance to heat and antibiotic stresses in Azotobacter vinelandii. FEMS Microbiol Lett 2022; 369:6824435. [PMID: 36368695 DOI: 10.1093/femsle/fnac104] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2022] [Revised: 08/29/2022] [Accepted: 10/31/2022] [Indexed: 11/13/2022] Open
Abstract
Bacteria have a mechanism to rescue stalled ribosomes known as trans-translation consisting of SsrA, a transfer-messenger RNA (tmRNA), and the small protein SmpB. Other alternative rescue mechanisms mediated by ArfA and ArfB proteins are present only in some species. Ribosome rescue mechanisms also play a role in tolerance to antibiotics and various stresses such as heat. This study shows that the genome of the soil bacterium A. vinelandii harbours genes encoding for tmRNA, SmpB, two paralogs of ArfA (arfA1 and arfA2), and ArfB. A number of mutant strains carrying mutations in the ssrA, arfA1, arfA2, and arfB genes were constructed and tested for their growth and susceptibility to heat and the antibiotic tetracycline. We found that the inactivation of both ssrA and one or the two arfA genes was detrimental to growth and caused a higher susceptibility to heat and to the antibiotic tetracycline. Interestingly, the arfB mutant strain was unable to grow after 2 h of incubation at 45°C. Inactivation of arfB in the ssrA-arfA1-arfA2 strain caused a lethal phenotype since the quadruple mutant could not be isolated. Taken together, our data suggest that both arfA1 and arfA2, as well as arfB, are functional as back up mechanisms, and that the ArfB pathway has an essential role that confers A. vinelandii resistance to high temperatures.
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Affiliation(s)
- Soledad Moreno
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Av. Universidad 2001, Col. Chamilpa, Cuernavaca, Morelos 62210, México
| | - Luis Felipe Muriel-Millán
- Departamento de Biología Molecular y Biotecnología, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, 04510 Ciudad Universitaria, CDMX, México
| | - Karen Rodríguez-Martínez
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Av. Universidad 2001, Col. Chamilpa, Cuernavaca, Morelos 62210, México
| | - Cristian Ortíz-Vasco
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Av. Universidad 2001, Col. Chamilpa, Cuernavaca, Morelos 62210, México
| | - Leidy Patricia Bedoya-Pérez
- Programa de Biología Sintética, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Av. Universidad 2001, Col. Chamilpa, Cuernavaca, Morelos 62210, México
| | - Guadalupe Espín
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Av. Universidad 2001, Col. Chamilpa, Cuernavaca, Morelos 62210, México
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26
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Rnf and Fix Have Specific Roles during Aerobic Nitrogen Fixation in Azotobacter vinelandii. Appl Environ Microbiol 2022; 88:e0104922. [PMID: 36000884 PMCID: PMC9469703 DOI: 10.1128/aem.01049-22] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Biological nitrogen fixation requires large amounts of energy in the form of ATP and low potential electrons to overcome the high activation barrier for cleavage of the dinitrogen triple bond. The model aerobic nitrogen-fixing bacteria, Azotobacter vinelandii, generates low potential electrons in the form of reduced ferredoxin (Fd) and flavodoxin (Fld) using two distinct mechanisms via the enzyme complexes Rnf and Fix. Both Rnf and Fix are expressed during nitrogen fixation, but deleting either rnf1 or fix genes has little effect on diazotrophic growth. However, deleting both rnf1 and fix eliminates the ability to grow diazotrophically. Rnf and Fix both use NADH as a source of electrons, but overcoming the energetics of NADH's endergonic reduction of Fd/Fld is accomplished through different mechanisms. Rnf harnesses free energy from the chemiosmotic potential, whereas Fix uses electron bifurcation to effectively couple the endergonic reduction of Fd/Fld to the exergonic reduction of quinone. Different reaction stoichiometries and condition-specific differential gene expression indicate specific roles for the two reactions. This work's complementary physiological studies and thermodynamic modeling reveal how Rnf and Fix balance redox homeostasis in various conditions. Specifically, the Fix complex is required for efficient growth under low oxygen concentrations, while Rnf is presumed to maintain reduced Fd/Fld production for nitrogenase under standard conditions. This work provides a framework for understanding how the production of low potential electrons sustains robust nitrogen fixation in various conditions. IMPORTANCE The availability of fixed nitrogen is critical for life in many ecosystems, from extreme environments to agriculture. Due to the energy demands of biological nitrogen fixation, organisms must tailor their metabolism during diazotrophic growth to deliver the energy requirements to nitrogenase in the form of ATP and low potential electrons. Therefore, a complete understanding of diazotrophic energy metabolism and redox homeostasis is required to understand the impact on ecological communities or to promote crop growth in agriculture through engineered diazotrophs.
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27
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Chowdhury NB, Alsiyabi A, Saha R. Characterizing the Interplay of Rubisco and Nitrogenase Enzymes in Anaerobic-Photoheterotrophically Grown Rhodopseudomonas palustris CGA009 through a Genome-Scale Metabolic and Expression Model. Microbiol Spectr 2022; 10:e0146322. [PMID: 35730964 PMCID: PMC9431616 DOI: 10.1128/spectrum.01463-22] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2022] [Accepted: 05/31/2022] [Indexed: 11/20/2022] Open
Abstract
Rhodopseudomonas palustris CGA009 is a Gram-negative purple nonsulfur bacterium that grows phototrophically by fixing carbon dioxide and nitrogen or chemotrophically by fixing or catabolizing a wide array of substrates, including lignin breakdown products for its carbon and fixing nitrogen for its nitrogen requirements. It can grow aerobically or anaerobically and can use light, inorganic, and organic compounds for energy production. Due to its ability to convert different carbon sources into useful products during anaerobic growth, this study reconstructed a metabolic and expression (ME) model of R. palustris to investigate its anaerobic-photoheterotrophic growth. Unlike metabolic (M) models, ME models include transcription and translation reactions along with macromolecules synthesis and couple these reactions with growth rate. This unique feature of the ME model led to nonlinear growth curve predictions, which matched closely with experimental growth rate data. At the theoretical maximum growth rate, the ME model suggested a diminishing rate of carbon fixation and predicted malate dehydrogenase and glycerol-3 phosphate dehydrogenase as alternate electron sinks. Moreover, the ME model also identified ferredoxin as a key regulator in distributing electrons between major redox balancing pathways. Because ME models include the turnover rate for each metabolic reaction, it was used to successfully capture experimentally observed temperature regulation of different nitrogenases. Overall, these unique features of the ME model demonstrated the influence of nitrogenases and rubiscos on R. palustris growth and predicted a key regulator in distributing electrons between major redox balancing pathways, thus establishing a platform for in silico investigation of R. palustris metabolism from a multiomics perspective. IMPORTANCE In this work, we reconstructed the first ME model for a purple nonsulfur bacterium (PNSB). Using the ME model, different aspects of R. palustris metabolism were examined. First, the ME model was used to analyze how reducing power entering the R. palustris cell through organic carbon sources gets partitioned into biomass, carbon dioxide fixation, and nitrogen fixation. Furthermore, the ME model predicted electron flux through ferredoxin as a major bottleneck in distributing electrons to nitrogenase enzymes. Next, the ME model characterized different nitrogenase enzymes and successfully recapitulated experimentally observed temperature regulations of those enzymes. Identifying the bottleneck responsible for transferring an electron to nitrogenase enzymes and recapitulating the temperature regulation of different nitrogenase enzymes can have profound implications in metabolic engineering, such as hydrogen production from R. palustris. Another interesting application of this ME model can be to take advantage of its redox balancing strategy to gain an understanding of the regulatory mechanism of biodegradable plastic production precursors, such as polyhydroxybutyrate (PHB).
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Affiliation(s)
- Niaz Bahar Chowdhury
- Chemical and Biomolecular Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska, USA
| | - Adil Alsiyabi
- Chemical and Biomolecular Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska, USA
| | - Rajib Saha
- Chemical and Biomolecular Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska, USA
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28
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Pi HW, Lin JJ, Chen CA, Wang PH, Chiang YR, Huang CC, Young CC, Li WH. Origin and evolution of nitrogen fixation in prokaryotes. Mol Biol Evol 2022; 39:6673025. [PMID: 35993177 PMCID: PMC9447857 DOI: 10.1093/molbev/msac181] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
The origin of nitrogen fixation is an important issue in evolutionary biology. While nitrogen is required by all living organisms, only a small fraction of bacteria and archaea can fix nitrogen. The prevailing view is that nitrogen fixation first evolved in archaea and was later transferred to bacteria. However, nitrogen-fixing (Nif) bacteria are far larger in number and far more diverse in ecological niches than Nif archaea. We, therefore, propose the bacteria-first hypothesis, which postulates that nitrogen fixation first evolved in bacteria and was later transferred to archaea. As >30,000 prokaryotic genomes have been sequenced, we conduct an in-depth comparison of the two hypotheses. We first identify the six genes involved in nitrogen fixation in all sequenced prokaryotic genomes and then reconstruct phylogenetic trees using the six Nif proteins individually or in combination. In each of these trees, the earliest lineages are bacterial Nif protein sequences and in the oldest clade (group) the archaeal sequences are all nested inside bacterial sequences, suggesting that the Nif proteins first evolved in bacteria. The bacteria-first hypothesis is further supported by the observation that the majority of Nif archaea carry the major bacterial Mo (molybdenum) transporter (ModABC) rather than the archaeal Mo transporter (WtpABC). Moreover, in our phylogeny of all available ModA and WtpA protein sequences, the earliest lineages are bacterial sequences while archaeal sequences are nested inside bacterial sequences. Furthermore, the bacteria-first hypothesis is supported by available isotopic data. In conclusion, our study strongly supports the bacteria-first hypothesis.
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Affiliation(s)
- Hong Wei Pi
- Ph.D. Program in Microbial Genomics, National Chung Hsing University and Academia Sinica, Taiwan.,Biodiversity Research Center, Academia Sinica, Taipei, Taiwan 11529
| | - Jinn Jy Lin
- Biodiversity Research Center, Academia Sinica, Taipei, Taiwan 11529
| | - Chi An Chen
- Biodiversity Research Center, Academia Sinica, Taipei, Taiwan 11529.,Genome and Systems Biology Degree Program, Academia Sinica and National Taiwan University, Taipei 10617, Taiwan
| | - Po Hsiang Wang
- Graduate Institute of Environmental Engineering, National Central University, Taoyuan, Taiwan 32001.,Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo, Japan 145-0061
| | - Yin Ru Chiang
- Biodiversity Research Center, Academia Sinica, Taipei, Taiwan 11529
| | - Chieh Chen Huang
- Department of Life Sciences, National Chung Hsing University, Taichung, Taiwan 402
| | - Chiu Chung Young
- Department of Soil and Environmental Sciences, College of Agriculture and Natural Resources, National Chung Hsing University, Taichung, Taiwan 402
| | - Wen Hsiung Li
- Biodiversity Research Center, Academia Sinica, Taipei, Taiwan 11529.,Department of Ecology and Evolution, University of Chicago, Chicago 60637, USA
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29
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Stripp ST, Duffus BR, Fourmond V, Léger C, Leimkühler S, Hirota S, Hu Y, Jasniewski A, Ogata H, Ribbe MW. Second and Outer Coordination Sphere Effects in Nitrogenase, Hydrogenase, Formate Dehydrogenase, and CO Dehydrogenase. Chem Rev 2022; 122:11900-11973. [PMID: 35849738 PMCID: PMC9549741 DOI: 10.1021/acs.chemrev.1c00914] [Citation(s) in RCA: 55] [Impact Index Per Article: 27.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Gases like H2, N2, CO2, and CO are increasingly recognized as critical feedstock in "green" energy conversion and as sources of nitrogen and carbon for the agricultural and chemical sectors. However, the industrial transformation of N2, CO2, and CO and the production of H2 require significant energy input, which renders processes like steam reforming and the Haber-Bosch reaction economically and environmentally unviable. Nature, on the other hand, performs similar tasks efficiently at ambient temperature and pressure, exploiting gas-processing metalloenzymes (GPMs) that bind low-valent metal cofactors based on iron, nickel, molybdenum, tungsten, and sulfur. Such systems are studied to understand the biocatalytic principles of gas conversion including N2 fixation by nitrogenase and H2 production by hydrogenase as well as CO2 and CO conversion by formate dehydrogenase, carbon monoxide dehydrogenase, and nitrogenase. In this review, we emphasize the importance of the cofactor/protein interface, discussing how second and outer coordination sphere effects determine, modulate, and optimize the catalytic activity of GPMs. These may comprise ionic interactions in the second coordination sphere that shape the electron density distribution across the cofactor, hydrogen bonding changes, and allosteric effects. In the outer coordination sphere, proton transfer and electron transfer are discussed, alongside the role of hydrophobic substrate channels and protein structural changes. Combining the information gained from structural biology, enzyme kinetics, and various spectroscopic techniques, we aim toward a comprehensive understanding of catalysis beyond the first coordination sphere.
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Affiliation(s)
- Sven T Stripp
- Freie Universität Berlin, Experimental Molecular Biophysics, Berlin 14195, Germany
| | | | - Vincent Fourmond
- Laboratoire de Bioénergétique et Ingénierie des Protéines, Institut de Microbiologie de la Méditerranée, Institut Microbiologie, Bioénergies et Biotechnologie, CNRS, Aix Marseille Université, Marseille 13402, France
| | - Christophe Léger
- Laboratoire de Bioénergétique et Ingénierie des Protéines, Institut de Microbiologie de la Méditerranée, Institut Microbiologie, Bioénergies et Biotechnologie, CNRS, Aix Marseille Université, Marseille 13402, France
| | - Silke Leimkühler
- University of Potsdam, Molecular Enzymology, Potsdam 14476, Germany
| | - Shun Hirota
- Nara Institute of Science and Technology, Division of Materials Science, Graduate School of Science and Technology, Nara 630-0192, Japan
| | - Yilin Hu
- Department of Molecular Biology & Biochemistry, University of California, Irvine, California 92697-3900, United States
| | - Andrew Jasniewski
- Department of Molecular Biology & Biochemistry, University of California, Irvine, California 92697-3900, United States
| | - Hideaki Ogata
- Nara Institute of Science and Technology, Division of Materials Science, Graduate School of Science and Technology, Nara 630-0192, Japan
- Hokkaido University, Institute of Low Temperature Science, Sapporo 060-0819, Japan
- Graduate School of Science, University of Hyogo, Hyogo 678-1297, Japan
| | - Markus W Ribbe
- Department of Molecular Biology & Biochemistry, University of California, Irvine, California 92697-3900, United States
- Department of Chemistry, University of California, Irvine, California 92697-2025, United States
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30
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Rnf1 is the primary electron source to nitrogenase in a high-ammonium-accumulating strain of Azotobacter vinelandii. Appl Microbiol Biotechnol 2022; 106:5051-5061. [PMID: 35804159 DOI: 10.1007/s00253-022-12059-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Revised: 06/24/2022] [Accepted: 06/28/2022] [Indexed: 11/02/2022]
Abstract
The enzyme nitrogenase performs the process of biological nitrogen fixation (BNF), converting atmospheric dinitrogen gas into the biologically accessible ammonia, which is rapidly protonated at physiological pH to yield ammonium. The reduction of dinitrogen requires both ATP and electrons. Azotobacter vinelandii is an aerobic nitrogen-fixing microbe that is a model organism for the study of BNF. Previous reports have described strains of A. vinelandii that are partially deregulated for BNF, resulting in the release of large quantities of ammonium into the growth medium. Determining the source of the electrons required to drive BNF is complicated by the existence of several protein complexes in A. vinelandii that have been linked to BNF in other species. In this work, we used the high-ammonium-accumulating strains of A. vinelandii to probe the source of electrons to nitrogenase by disrupting the Rnf1 and Fix complexes. The results of this work demonstrate the potential of these strains to be used as a tool to investigate the contributions of other enzymes or complexes in the process of BNF. These results provide strong evidence that the Rnf1 complex of A. vinelandii is the primary source of electrons delivered to the nitrogenase enzyme in this partially deregulated strain. The Fix complex under native regulation was unable to provide sufficient electrons to accumulate extracellular ammonium in the absence of the Rnf1 complex. Increased ammonium accumulation could be attained in a strain lacking the Rnf1 complex if the genes of the Fix protein complex were relocated behind the strong promoter of the S-layer protein but still failed to achieve the levels found with just the Rnf1 complex by itself. KEY POINTS: • The Rnf1 complex is integral to ammonium accumulation in A. vinelandii. • The Fix complex can be deleted and still achieve ammonium accumulation in A. vinelandii. • A. vinelandii can be engineered to increase the contribution of the Fix complex to ammonium accumulation.
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31
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Bulk and Spatially Resolved Extracellular Metabolome of Free-Living Nitrogen Fixation. Appl Environ Microbiol 2022; 88:e0050522. [PMID: 35652664 PMCID: PMC9238392 DOI: 10.1128/aem.00505-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
Soil nitrogen (N) transformations constrain terrestrial net primary productivity and are driven by the activity of soil microorganisms. Free-living N fixation (FLNF) is an important soil N transformation and key N input to terrestrial systems, but the forms of N contributed to soil by FLNF are poorly understood. To address this knowledge gap, a focus on microorganisms and microbial scale processes is needed that links N-fixing bacteria and their contributed N sources to FLNF process rates. However, studying the activity of soil microorganisms in situ poses inherent challenges, including differences in sampling scale between microorganism and process rates, which can be addressed with culture-based studies and an emphasis on microbial-scale measurements. Culture conditions can differ significantly from soil conditions, so it also important that such studies include multiple culture conditions like liquid and solid media as proxies for soil environments like soil pore water and soil aggregate surfaces. Here we characterized extracellular N-containing metabolites produced by two common, diazotrophic soil bacteria in liquid and solid media, with or without N, across two sampling scales (bulk via GC-MS and spatially resolved via MALDI mass spec imaging). We found extracellular production of inorganic and organic N during FLNF, indicating terrestrial N contributions from FLNF occur in multiple forms not only as ammonium as previously thought. Extracellular metabolite profiles differed between liquid and solid media supporting previous work indicating environmental structure influences microbial function. Metabolite profiles also differed between sampling scales underscoring the need to quantify microbial scale conditions to accurately interpret microbial function. IMPORTANCE Free-living nitrogen-fixing bacteria contribute significantly to terrestrial nitrogen availability; however, the forms of nitrogen contributed by this process are poorly understood. This is in part because of inherent challenges to studying soil microorganisms in situ, such as vast differences in scale between microorganism and ecosystem and complexities of the soil system (e.g., opacity, chemical complexity). Thus, upscaling important ecosystem processes driven by soil microorganisms, like free-living nitrogen fixation, requires microbial-scale measurements in controlled systems. Our work generated bulk and spatially resolved measurements of nitrogen released during free-living nitrogen fixation under two contrasting growth conditions analogous to soil pores and aggregates. This work allowed us to determine that diverse forms of nitrogen are likely contributed to terrestrial systems by free-living nitrogen bacteria. We also demonstrated that microbial habitat (e.g., liquid versus solid media) alters microbial activity and that measurement of microbial activity is altered by sampling scale (e.g., bulk versus spatially resolved) highlighting the critical importance of quantifying microbial-scale processes to upscaling of ecosystem function.
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Boutet E, Djerroud S, Perreault J. Small RNAs beyond Model Organisms: Have We Only Scratched the Surface? Int J Mol Sci 2022; 23:ijms23084448. [PMID: 35457265 PMCID: PMC9029176 DOI: 10.3390/ijms23084448] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2022] [Revised: 04/14/2022] [Accepted: 04/15/2022] [Indexed: 01/27/2023] Open
Abstract
Small RNAs (sRNAs) are essential regulators in the adaptation of bacteria to environmental changes and act by binding targeted mRNAs through base complementarity. Approximately 550 distinct families of sRNAs have been identified since their initial characterization in the 1980s, accelerated by the emergence of RNA-sequencing. Small RNAs are found in a wide range of bacterial phyla, but they are more prominent in highly researched model organisms compared to the rest of the sequenced bacteria. Indeed, Escherichia coli and Salmonella enterica contain the highest number of sRNAs, with 98 and 118, respectively, with Enterobacteriaceae encoding 145 distinct sRNAs, while other bacteria families have only seven sRNAs on average. Although the past years brought major advances in research on sRNAs, we have perhaps only scratched the surface, even more so considering RNA annotations trail behind gene annotations. A distinctive trend can be observed for genes, whereby their number increases with genome size, but this is not observable for RNAs, although they would be expected to follow the same trend. In this perspective, we aimed at establishing a more accurate representation of the occurrence of sRNAs in bacteria, emphasizing the potential for novel sRNA discoveries.
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33
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DePoy AN, King GM. Putative Nickel-Dependent Anaerobic Carbon Monoxide Uptake Occurs Commonly in Soils and Sediments at Ambient Temperature and Might Contribute to Atmospheric and Sub-Atmospheric Carbon Monoxide Uptake During Anoxic Conditions. Front Microbiol 2022; 13:736189. [PMID: 35401450 PMCID: PMC8987735 DOI: 10.3389/fmicb.2022.736189] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2021] [Accepted: 02/18/2022] [Indexed: 11/13/2022] Open
Abstract
Carbon monoxide (CO) occurs naturally in the atmosphere where it plays a critical role in tropospheric chemistry. Atmospheric CO uptake by soils has been well documented as an important CO sink and has been attributed to a group of aerobic bacteria that possess a molybdenum-dependent CO dehydrogenase (Mo-CODH). CO can also be oxidized by obligate Ni-dependent anaerobes (Ni-COX) that possess nickel-dependent CODHs (Ni-CODH) but relatively little is known about their ecology or their potential to contribute to CO dynamics within soils and sediments or to soil-atmosphere CO exchanges. Results from a series of assays undertaken with diverse soils and sediments and CO concentrations of 10 ppm and 25% with incubation temperatures of 10, 25, and 60°C revealed anaerobic uptake rates with 10 ppm CO that were comparable to those measured under oxic conditions; further, anaerobic CO uptake occurred without a lag and at atmospheric and sub-atmospheric CO concentrations. Assays with 25% CO revealed previously undocumented activity at 10°C and showed extensive activity at 25°C. Results from prior studies with isolates and soils suggest that anaerobic uptake at both 10 ppm and 25% CO concentrations might be attributed to Ni-COX. Collectively the results considerably expand the ecological range for Ni-COX and indicate that they could play previously unsuspected roles in soil CO dynamics.
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Takimoto R, Tatemichi Y, Aoki W, Kosaka Y, Minakuchi H, Ueda M, Kuroda K. A critical role of an oxygen-responsive gene for aerobic nitrogenase activity in Azotobacter vinelandii and its application to Escherichia coli. Sci Rep 2022; 12:4182. [PMID: 35264690 PMCID: PMC8907163 DOI: 10.1038/s41598-022-08007-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2021] [Accepted: 02/28/2022] [Indexed: 12/02/2022] Open
Abstract
Since nitrogenase is irreversibly inactivated within a few minutes after exposure to oxygen, current studies on the heterologous expression of nitrogenase are limited to anaerobic conditions. This study comprehensively identified genes showing oxygen-concentration-dependent expression only under nitrogen-fixing conditions in Azotobacter vinelandii, an aerobic diazotroph. Among the identified genes, nafU, with an unknown function, was greatly upregulated under aerobic nitrogen-fixing conditions. Through replacement and overexpressing experiments, we suggested that nafU is involved in the maintenance of nitrogenase activity under aerobic nitrogenase activity. Furthermore, heterologous expression of nafU in nitrogenase-producing Escherichia coli increased nitrogenase activity under aerobic conditions by 9.7 times. Further analysis of NafU protein strongly suggested its localization in the inner membrane and raised the possibility that this protein may lower the oxygen concentration inside the cells. These findings provide new insights into the mechanisms for maintaining stable nitrogenase activity under aerobic conditions in A. vinelandii and provide a platform to advance the use of nitrogenase under aerobic conditions.
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Affiliation(s)
- Ren Takimoto
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto, 606-8502, Japan
| | - Yuki Tatemichi
- Research and Development Division, Kikkoman Corporation, 338 Noda, Noda, Chiba, 278-0037, Japan
| | - Wataru Aoki
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto, 606-8502, Japan
| | - Yuishin Kosaka
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto, 606-8502, Japan
| | | | - Mitsuyoshi Ueda
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto, 606-8502, Japan
| | - Kouichi Kuroda
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto, 606-8502, Japan.
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35
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Pérez‐González A, Jimenez‐Vicente E, Salinero‐Lanzarote A, Harris DF, Seefeldt LC, Dean DR. AnfO
controls fidelity of nitrogenase
FeFe
protein maturation by preventing misincorporation of
FeV
‐cofactor. Mol Microbiol 2022; 117:1080-1088. [PMID: 35220629 PMCID: PMC9310841 DOI: 10.1111/mmi.14890] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2021] [Revised: 02/22/2022] [Accepted: 02/23/2022] [Indexed: 11/26/2022]
Abstract
Azotobacter vinelandii produces three genetically distinct, but structurally and mechanistically similar nitrogenase isozymes designated as Mo‐dependent, V‐dependent, or Fe‐only based on the heterometal contained within their associated active site cofactors. These catalytic cofactors, which provide the site for N2 binding and reduction, are, respectively, designated as FeMo‐cofactor, FeV‐cofactor, and FeFe‐cofactor. Fe‐only nitrogenase is a poor catalyst for N2 fixation, when compared to the Mo‐dependent and V‐dependent nitrogenases and is only produced when neither Mo nor V is available. Under conditions favoring the production of Fe‐only nitrogenase a gene product designated AnfO preserves the fidelity of Fe‐only nitrogenase by preventing the misincorporation of FeV‐cofactor, which results in the accumulation of a hybrid enzyme that cannot reduce N2. These results are interpreted to indicate that AnfO controls the fidelity of Fe‐only nitrogenase maturation during the physiological transition from conditions that favor V‐dependent nitrogenase utilization to Fe‐only nitrogenase utilization to support diazotrophic growth.
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Affiliation(s)
| | | | - Alvaro Salinero‐Lanzarote
- Centro de Biotecnología y Genómica de Plantas, Universidad Politécnica de Madrid, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Pozuelo de Alarcón, 28223 Madrid Spain
| | - Derek F. Harris
- Department of Chemistry and Biochemistry Utah State University Logan UT USA
| | - Lance C. Seefeldt
- Department of Chemistry and Biochemistry Utah State University Logan UT USA
| | - Dennis R. Dean
- Department of Biochemistry, Virginia Tech, Blacksburg Virginia USA
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Genetic determinants of ammonium excretion in nifL mutants of Azotobacter vinelandii. Appl Environ Microbiol 2022; 88:e0187621. [PMID: 35138932 DOI: 10.1128/aem.01876-21] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The ubiquitous diazotrophic soil bacterium Azotobacter vinelandii has been extensively studied as a model organism for biological nitrogen fixation (BNF). In A. vinelandii, BNF is regulated by the NifL-NifA two-component system, where NifL acts as an anti-activator that tightly controls the activity of the nitrogen fixation specific transcriptional activator, NifA, in response to redox, nitrogen, and carbon status. While several studies reported mutations in A. vinelandii nifL resulted in the deregulation of nitrogenase expression and the release of large quantities of ammonium, knowledge about the specific determinants for this ammonium-excreting phenotype is lacking. In this work, we report that only specific disruptions of nifL lead to large quantities of ammonium accumulated in liquid culture (∼12 mM). The ammonium excretion phenotype is solely associated with deletions of NifL domains combined with the insertion of a promoter sequence in the opposite orientation to nifLA transcription. We further demonstrated that the strength of the inserted promoter could influence the amounts of ammonium excreted by affecting rnf1 gene expression as an additional requirement for ammonium excretion. These ammonium-excreting nifL mutants significantly stimulate the transfer of fixed nitrogen to rice. This work defines discrete determinants that bring about A. vinelandii ammonium excretion and demonstrates that strains can be generated through simple gene editing to provide promising biofertilizers capable of transferring nitrogen to crops. Importance There is a considerable interest in the engineering of ammonium-excreting bacteria for use in agriculture to promote the growth of plants under fixed nitrogen-limiting conditions. This work defines discrete determinants that bring about A. vinelandii ammonium excretion and demonstrates that strains can be generated through simple gene editing to provide promising biofertilizers capable of transferring nitrogen to crops.
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Dudun AA, Akoulina EA, Zhuikov VA, Makhina TK, Voinova VV, Belishev NV, Khaydapova DD, Shaitan KV, Bonartseva GA, Bonartsev AP. Competitive Biosynthesis of Bacterial Alginate Using Azotobacter vinelandii 12 for Tissue Engineering Applications. Polymers (Basel) 2021; 14:polym14010131. [PMID: 35012152 PMCID: PMC8747204 DOI: 10.3390/polym14010131] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2021] [Revised: 12/17/2021] [Accepted: 12/23/2021] [Indexed: 11/16/2022] Open
Abstract
This study investigated the effect of various cultivation conditions (sucrose/phosphate concentrations, aeration level) on alginate biosynthesis using the bacterial producing strain Azotobacter vinelandii 12 by the full factorial design (FFD) method and physicochemical properties (e.g., rheological properties) of the produced bacterial alginate. We demonstrated experimentally the applicability of bacterial alginate for tissue engineering (the cytotoxicity testing using mesenchymal stem cells (MSCs)). The isolated synthesis of high molecular weight (Mw) capsular alginate with a high level of acetylation (25%) was achieved by FFD method under a low sucrose concentration, an increased phosphate concentration, and a high aeration level. Testing the viscoelastic properties and cytotoxicity showed that bacterial alginate with a maximal Mw (574 kDa) formed the densest hydrogels (which demonstrated relatively low cytotoxicity for MSCs in contrast to bacterial alginate with low Mw). The obtained data have shown promising prospects in controlled biosynthesis of bacterial alginate with different physicochemical characteristics for various biomedical applications including tissue engineering.
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Affiliation(s)
- Andrei A. Dudun
- Research Center of Biotechnology of the Russian Academy of Sciences Leninsky Ave, 33, Bld. 2, 119071 Moscow, Russia; (A.A.D.); (V.A.Z.); (T.K.M.); (G.A.B.)
| | - Elizaveta A. Akoulina
- Faculty of Biology, M.V. Lomonosov Moscow State University, Leninskie Gory 1-12, 119234 Moscow, Russia; (E.A.A.); (V.V.V.); (N.V.B.); (K.V.S.)
| | - Vsevolod A. Zhuikov
- Research Center of Biotechnology of the Russian Academy of Sciences Leninsky Ave, 33, Bld. 2, 119071 Moscow, Russia; (A.A.D.); (V.A.Z.); (T.K.M.); (G.A.B.)
| | - Tatiana K. Makhina
- Research Center of Biotechnology of the Russian Academy of Sciences Leninsky Ave, 33, Bld. 2, 119071 Moscow, Russia; (A.A.D.); (V.A.Z.); (T.K.M.); (G.A.B.)
| | - Vera V. Voinova
- Faculty of Biology, M.V. Lomonosov Moscow State University, Leninskie Gory 1-12, 119234 Moscow, Russia; (E.A.A.); (V.V.V.); (N.V.B.); (K.V.S.)
| | - Nikita V. Belishev
- Faculty of Biology, M.V. Lomonosov Moscow State University, Leninskie Gory 1-12, 119234 Moscow, Russia; (E.A.A.); (V.V.V.); (N.V.B.); (K.V.S.)
| | - Dolgor D. Khaydapova
- Department of Soil Physics and Reclamation, Soil Science Faculty, M.V. Lomonosov Moscow State University, Leninskie Gory 1-12, 119234 Moscow, Russia;
| | - Konstantin V. Shaitan
- Faculty of Biology, M.V. Lomonosov Moscow State University, Leninskie Gory 1-12, 119234 Moscow, Russia; (E.A.A.); (V.V.V.); (N.V.B.); (K.V.S.)
| | - Garina A. Bonartseva
- Research Center of Biotechnology of the Russian Academy of Sciences Leninsky Ave, 33, Bld. 2, 119071 Moscow, Russia; (A.A.D.); (V.A.Z.); (T.K.M.); (G.A.B.)
| | - Anton P. Bonartsev
- Faculty of Biology, M.V. Lomonosov Moscow State University, Leninskie Gory 1-12, 119234 Moscow, Russia; (E.A.A.); (V.V.V.); (N.V.B.); (K.V.S.)
- Correspondence: ; Tel.: +7-4959306306
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Metabolic Model of the Nitrogen-Fixing Obligate Aerobe Azotobacter vinelandii Predicts Its Adaptation to Oxygen Concentration and Metal Availability. mBio 2021; 12:e0259321. [PMID: 34903060 PMCID: PMC8686835 DOI: 10.1128/mbio.02593-21] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
There is considerable interest in promoting biological nitrogen fixation (BNF) as a mechanism to reduce the inputs of nitrogenous fertilizers in agriculture, but considerable fundamental knowledge gaps still need to be addressed. BNF is catalyzed by nitrogenase, which requires a large input of energy in the form of ATP and low potential electrons. Diazotrophs that respire aerobically have an advantage in meeting the ATP demands of BNF but face challenges in protecting nitrogenase from inactivation by oxygen. Here, we constructed a genome-scale metabolic model of the nitrogen-fixing bacterium Azotobacter vinelandii, which uses a complex respiratory protection mechanism to consume oxygen at a high rate to keep intracellular conditions microaerobic. Our model accurately predicts growth rate under high oxygen and substrate concentrations, consistent with a large electron flux directed to the respiratory protection mechanism. While a partially decoupled electron transport chain compensates for some of the energy imbalance under high-oxygen conditions, it does not account for all substrate intake, leading to increased maintenance rates. Interestingly, the respiratory protection mechanism is required for accurate predictions even when ammonia is supplemented during growth, suggesting that the respiratory protection mechanism might be a core principle of metabolism and not just used for nitrogenase protection. We have also shown that rearrangement of flux through the electron transport system allows A. vinelandii to adapt to different oxygen concentrations, metal availability, and genetic disruption, which cause an ammonia excretion phenotype. Accurately determining the energy balance in an aerobic nitrogen-fixing metabolic model is required for future engineering approaches.
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Structural analysis of the reductase component AnfH of iron-only nitrogenase from Azotobacter vinelandii. J Inorg Biochem 2021; 227:111690. [PMID: 34929539 DOI: 10.1016/j.jinorgbio.2021.111690] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2021] [Revised: 11/29/2021] [Accepted: 12/03/2021] [Indexed: 11/20/2022]
Abstract
Biological nitrogen fixation, the conversion of atmospheric dinitrogen into bioavailable ammonium, is exclusively catalyzed by the enzyme nitrogenase that is present in nitrogen-fixing organisms, the diazotrophs. So far, three different nitrogenase variants, encoded in their corresponding, distinct gene clusters, have been found in nature. Each one of these consists of a catalytic dinitrogenase component and a unique, ATP-dependent reductase, the Fe protein. The three variant nitrogenases differ in the composition of the active site and contain either molybdenum, vanadium or only iron in the dinitrogenase component. Here we present the 2.0 Å resolution crystal structure of the ADP-bound reductase component AnfH of the iron-only nitrogenase from the model diazotroph Azotobacter vinelandii. A comparison of this structure with the ones reported for the two other Fe protein homologs NifH and VnfH in the ADP-bound state shows that all are adopting the same conformation. However, cross-reactivity assays with the three nitrogenase homologs revealed AnfH to be compatible with iron-only nitrogenase and to a lesser degree with the vanadium-containing enzyme, but not with molybdenum nitrogenase.
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Abstract
Azotobacter vinelandii is a nitrogen-fixing free-living soil microbe that has been studied for decades in relation to biological nitrogen fixation (BNF). It is highly amenable to genetic manipulation, helping to unravel the intricate importance of different proteins involved in the process of BNF, including the biosynthesis of cofactors that are essential to assembling the complex metal cofactors that catalyze the difficult reaction of nitrogen fixation. Additionally, A. vinelandii accomplishes this feat while growing as an obligate aerobe, differentiating it from many of the nitrogen-fixing bacteria that are associated with plant roots. The ability to function in the presence of oxygen makes A. vinelandii suitable for application in various potential biotechnological schemes. In this study, we employed transposon sequencing (Tn-seq) to measure the fitness defects associated with disruptions of various genes under nitrogen-fixing dependent growth, versus growth with extraneously provided urea as a nitrogen source. The results allowed us to probe the importance of more than 3,800 genes, revealing that many genes previously believed to be important, can be successfully disrupted without impacting cellular fitness. IMPORTANCE These results provide insights into the functional redundancy in A. vinelandii, while also providing a direct measure of fitness for specific genes associated with the process of BNF. These results will serve as a valuable reference tool in future studies to uncover the mechanisms that govern this process.
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Kabasakal BV, Cotton CAR, Murray JW. Crystal structure of the [2Fe-2S] protein I (Shethna protein I) from Azotobacter vinelandii. Acta Crystallogr F Struct Biol Commun 2021; 77:407-411. [PMID: 34726179 PMCID: PMC8561814 DOI: 10.1107/s2053230x21009936] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2021] [Accepted: 09/23/2021] [Indexed: 11/10/2022] Open
Abstract
Azotobacter vinelandii is a model diazotroph and is the source of most nitrogenase material for structural and biochemical work. Azotobacter can grow in above-atmospheric levels of oxygen, despite the sensitivity of nitrogenase activity to oxygen. Azotobacter has many iron-sulfur proteins in its genome, which were identified as far back as the 1960s and probably play roles in the complex redox chemistry that Azotobacter must maintain when fixing nitrogen. Here, the 2.1 Å resolution crystal structure of the [2Fe-2S] protein I (Shethna protein I) from A. vinelandii is presented, revealing a homodimer with the [2Fe-2S] cluster coordinated by the surrounding conserved cysteine residues. It is similar to the structure of the thioredoxin-like [2Fe-2S] protein from Aquifex aeolicus, including the positions of the [2Fe-2S] clusters and conserved cysteine residues. The structure of Shethna protein I will provide information for understanding its function in relation to nitrogen fixation and its evolutionary relationships to other ferredoxins.
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Affiliation(s)
- Burak V. Kabasakal
- Department of Life Sciences, Imperial College London, Exhibition Road, London SW7 2AZ, United Kingdom
- Turkish Accelerator and Radiation Laboratory, Institute of Accelerator Technologies, Ankara University, Gölbaşı, 06830 Ankara, Turkey
| | - Charles A. R. Cotton
- Department of Life Sciences, Imperial College London, Exhibition Road, London SW7 2AZ, United Kingdom
- Cambrium GmbH, Max-Urich-Strasse 3, 13355 Berlin, Germany
| | - James W. Murray
- Department of Life Sciences, Imperial College London, Exhibition Road, London SW7 2AZ, United Kingdom
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42
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Bertsova YV, Serebryakova MV, Baykov AA, Bogachev AV. The flavin transferase ApbE flavinylates the ferredoxin:NAD+-oxidoreductase Rnf required for N2 fixation in Azotobacter vinelandii. FEMS Microbiol Lett 2021; 368:6381689. [PMID: 34610116 DOI: 10.1093/femsle/fnab130] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2021] [Accepted: 09/30/2021] [Indexed: 12/14/2022] Open
Abstract
Azotobacter vinelandii, the model microbe in nitrogen fixation studies, uses the ferredoxin:NAD+-oxidoreductase Rnf to regenerate ferredoxin (flavodoxin), acting as an electron donor for nitrogenase. However, the relative contribution of Rnf to nitrogenase functioning is unknown because this bacterium contains another ferredoxin reductase, FixABCX. Furthermore, Rnf is flavinylated in the cell, but the importance and pathway of this modification reaction also remain largely unknown. We constructed A. vinelandii cells with impaired activities of FixABCX and/or putative flavin transferase ApbE. The ApbE-deficient mutant could not produce covalently flavinylated membrane proteins and demonstrated markedly decreased flavodoxin:NAD+ oxidoreductase activity and significant growth defects under diazotrophic conditions. The double ΔFix/ΔApbE mutation abolished the flavodoxin:NAD+ oxidoreductase activity and the ability of A. vinelandii to grow in the absence of a fixed nitrogen source. ApbE flavinylated a truncated RnfG subunit of Rnf1 by forming a phosphoester bond between flavin mononucleotide and a threonine residue. These findings indicate that Rnf (presumably its Rnf1 form) is the major ferredoxin-reducing enzyme in the nitrogen fixation system and that the activity of Rnf depends on its covalent flavinylation by the flavin transferase ApbE.
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Affiliation(s)
- Yulia V Bertsova
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119234, Russia
| | - Marina V Serebryakova
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119234, Russia
| | - Alexander A Baykov
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119234, Russia
| | - Alexander V Bogachev
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119234, Russia
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43
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Tatemichi Y, Nakahara T, Ueda M, Kuroda K. Construction of recombinant Escherichia coli producing nitrogenase-related proteins from Azotobacter vinelandii. Biosci Biotechnol Biochem 2021; 85:2209-2216. [PMID: 34387317 DOI: 10.1093/bbb/zbab144] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2021] [Accepted: 08/05/2021] [Indexed: 11/12/2022]
Abstract
Biological nitrogen fixation by nitrogenase has attracted attention as an alternative method to chemical nitrogen fixation, which requires large amounts of fossil fuels. Azotobacter vinelandii, which produces an oxygen-sensitive nitrogenase, can fix nitrogen even under aerobic conditions; therefore, the heterologous expression of nif-related genes from A. vinelandii is a promising strategy for developing a biological nitrogen fixation method. We assembled 17 nif-related genes, which are scattered throughout the genome of A. vinelandii, into synthetic gene clusters by overlap-extension-PCR and seamless cloning and expressed them in Escherichia coli. The transcription and translation of the 17 nif-related genes were evaluated by RT-qPCR and LC-MS/MS, respectively. The constructed E. coli showed nitrogenase activity under anaerobic and microaerobic conditions. This strain would be a useful model for examining the effect of other genes from A. vinelandii on nitrogen fixation by expressing them in addition to the minimal set of nif-related genes.
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Affiliation(s)
- Yuki Tatemichi
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-Ku, Kyoto, Japan
- Research and Development Division, Kikkoman Corporation, Noda-City, Chiba, Japan
| | - Takeharu Nakahara
- Research and Development Division, Kikkoman Corporation, Noda-City, Chiba, Japan
| | - Mitsuyoshi Ueda
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-Ku, Kyoto, Japan
| | - Kouichi Kuroda
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-Ku, Kyoto, Japan
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44
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Mitra R, Xu T, Chen GQ, Xiang H, Han J. An updated overview on the regulatory circuits of polyhydroxyalkanoates synthesis. Microb Biotechnol 2021; 15:1446-1470. [PMID: 34473895 PMCID: PMC9049629 DOI: 10.1111/1751-7915.13915] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Revised: 08/20/2021] [Accepted: 08/23/2021] [Indexed: 11/30/2022] Open
Abstract
Polyhydroxyalkanoates (PHA) are a promising and sustainable alternative to the petroleum‐based synthetic plastics. Regulation of PHA synthesis is receiving considerable importance as engineering the regulatory factors might help developing strains with improved PHA‐producing abilities. PHA synthesis is dedicatedly regulated by a number of regulatory networks. They tightly control the PHA content, granule size and their distribution in cells. Most PHA‐accumulating microorganisms have multiple regulatory networks that impart a combined effect on PHA metabolism. Among them, several factors ranging from global to specific regulators, have been identified and characterized till now. This review is an attempt to categorically summarize the diverse regulatory circuits that operate in some important PHA‐producing microorganisms. However, in several organisms, the detailed mechanisms involved in the regulation of PHA synthesis is not well‐explored and hence further research is needed. The information presented in this review might help researcher to identify the prevailing research gaps in PHA regulation.
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Affiliation(s)
- Ruchira Mitra
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, 100101, China.,International College, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Tong Xu
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, 100101, China
| | - Guo-Qiang Chen
- Center for Synthetic and Systems Biology, School of Life Sciences, Tsinghua University, Beijing, China
| | - Hua Xiang
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, 100101, China.,College of Life Science, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Jing Han
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, 100101, China.,College of Life Science, University of Chinese Academy of Sciences, Beijing, 100049, China
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45
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Ponce B, Urtuvia V, Maturana N, Peña C, Díaz-Barrera A. Increases in alginate production and transcription levels of alginate lyase (alyA1) by control of the oxygen transfer rate in Azotobacter vinelandii cultures under diazotrophic conditions. ELECTRON J BIOTECHN 2021. [DOI: 10.1016/j.ejbt.2021.04.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
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46
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Carruthers BM, Garcia AK, Rivier A, Kacar B. Automated Laboratory Growth Assessment and Maintenance of Azotobacter vinelandii. Curr Protoc 2021; 1:e57. [PMID: 33656286 DOI: 10.1002/cpz1.57] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Azotobacter vinelandii (A. vinelandii) is a commonly used model organism for the study of aerobic respiration, the bacterial production of several industrially relevant compounds, and, perhaps most significantly, the genetics and biochemistry of biological nitrogen fixation. Laboratory growth assessments of A. vinelandii are useful for evaluating the impact of environmental and genetic modifications on physiological properties, including diazotrophy. However, researchers typically rely on manual growth methods that are oftentimes laborious and inefficient. We present a protocol for the automated growth assessment of A. vinelandii on a microplate reader, particularly well-suited for studies of diazotrophic growth. We discuss common pitfalls and strategies for protocol optimization, and demonstrate the protocol's application toward growth evaluation of strains carrying modifications to nitrogen-fixation genes. © 2021 The Authors. Basic Protocol 1: Preparation of A. vinelandii plate cultures from frozen stock Basic Protocol 2: Preparation of A. vinelandii liquid precultures Basic Protocol 3: Automated growth rate experiment of A. vinelandii on a microplate reader.
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Affiliation(s)
- Brooke M Carruthers
- Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona
| | - Amanda K Garcia
- Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona
| | - Alex Rivier
- Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona
| | - Betul Kacar
- Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona.,Department of Astronomy and Steward Observatory, University of Arizona, Tucson, Arizona.,Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona
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47
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Bueno Batista M, Brett P, Appia-Ayme C, Wang YP, Dixon R. Disrupting hierarchical control of nitrogen fixation enables carbon-dependent regulation of ammonia excretion in soil diazotrophs. PLoS Genet 2021; 17:e1009617. [PMID: 34111137 PMCID: PMC8219145 DOI: 10.1371/journal.pgen.1009617] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Revised: 06/22/2021] [Accepted: 05/23/2021] [Indexed: 12/14/2022] Open
Abstract
The energetic requirements for biological nitrogen fixation necessitate stringent regulation of this process in response to diverse environmental constraints. To ensure that the nitrogen fixation machinery is expressed only under appropriate physiological conditions, the dedicated NifL-NifA regulatory system, prevalent in Proteobacteria, plays a crucial role in integrating signals of the oxygen, carbon and nitrogen status to control transcription of nitrogen fixation (nif) genes. Greater understanding of the intricate molecular mechanisms driving transcriptional control of nif genes may provide a blueprint for engineering diazotrophs that associate with cereals. In this study, we investigated the properties of a single amino acid substitution in NifA, (NifA-E356K) which disrupts the hierarchy of nif regulation in response to carbon and nitrogen status in Azotobacter vinelandii. The NifA-E356K substitution enabled overexpression of nitrogenase in the presence of excess fixed nitrogen and release of ammonia outside the cell. However, both of these properties were conditional upon the nature of the carbon source. Our studies reveal that the uncoupling of nitrogen fixation from its assimilation is likely to result from feedback regulation of glutamine synthetase, allowing surplus fixed nitrogen to be excreted. Reciprocal substitutions in NifA from other Proteobacteria yielded similar properties to the A. vinelandii counterpart, suggesting that this variant protein may facilitate engineering of carbon source-dependent ammonia excretion amongst diverse members of this family.
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Affiliation(s)
| | - Paul Brett
- Department of Metabolic Biology, John Innes Centre, Norwich, United Kingdom
| | - Corinne Appia-Ayme
- Department of Molecular Microbiology, John Innes Centre, Norwich, United Kingdom
| | - Yi-Ping Wang
- State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences & School of Advanced Agricultural Sciences, Peking University, Beijing, China
| | - Ray Dixon
- Department of Molecular Microbiology, John Innes Centre, Norwich, United Kingdom
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48
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Borisov VB, Siletsky SA, Paiardini A, Hoogewijs D, Forte E, Giuffrè A, Poole RK. Bacterial Oxidases of the Cytochrome bd Family: Redox Enzymes of Unique Structure, Function, and Utility As Drug Targets. Antioxid Redox Signal 2021; 34:1280-1318. [PMID: 32924537 PMCID: PMC8112716 DOI: 10.1089/ars.2020.8039] [Citation(s) in RCA: 36] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/20/2020] [Revised: 09/01/2020] [Accepted: 09/02/2020] [Indexed: 12/23/2022]
Abstract
Significance: Cytochrome bd is a ubiquinol:oxygen oxidoreductase of many prokaryotic respiratory chains with a unique structure and functional characteristics. Its primary role is to couple the reduction of molecular oxygen, even at submicromolar concentrations, to water with the generation of a proton motive force used for adenosine triphosphate production. Cytochrome bd is found in many bacterial pathogens and, surprisingly, in bacteria formally denoted as anaerobes. It endows bacteria with resistance to various stressors and is a potential drug target. Recent Advances: We summarize recent advances in the biochemistry, structure, and physiological functions of cytochrome bd in the light of exciting new three-dimensional structures of the oxidase. The newly discovered roles of cytochrome bd in contributing to bacterial protection against hydrogen peroxide, nitric oxide, peroxynitrite, and hydrogen sulfide are assessed. Critical Issues: Fundamental questions remain regarding the precise delineation of electron flow within this multihaem oxidase and how the extraordinarily high affinity for oxygen is accomplished, while endowing bacteria with resistance to other small ligands. Future Directions: It is clear that cytochrome bd is unique in its ability to confer resistance to toxic small molecules, a property that is significant for understanding the propensity of pathogens to possess this oxidase. Since cytochrome bd is a uniquely bacterial enzyme, future research should focus on harnessing fundamental knowledge of its structure and function to the development of novel and effective antibacterial agents.
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Affiliation(s)
- Vitaliy B. Borisov
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russian Federation
| | - Sergey A. Siletsky
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russian Federation
| | | | - David Hoogewijs
- Department of Medicine/Physiology, University of Fribourg, Fribourg, Switzerland
| | - Elena Forte
- Department of Biochemical Sciences, Sapienza University of Rome, Rome, Italy
| | | | - Robert K. Poole
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Sheffield, United Kingdom
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Velázquez-Sánchez C, Vences-Guzmán MÁ, Moreno S, Tinoco-Valencia R, Espín G, Guzmán J, Sahonero-Canavesi DX, Sohlenkamp C, Segura D. PsrA positively regulates the unsaturated fatty acid synthesis operon fabAB in Azotobacter vinelandii. Microbiol Res 2021; 249:126775. [PMID: 33964629 DOI: 10.1016/j.micres.2021.126775] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2020] [Revised: 03/12/2021] [Accepted: 04/27/2021] [Indexed: 10/21/2022]
Abstract
In Pseudomonas spp. PsrA, a transcriptional activator of the rpoS gene, regulates fatty acid catabolism by repressing the fadBA5 β-oxidation operon. In Azotobacter vinelandii, a soil bacterium closely related to Pseudomonas species, PsrA is also an activator of rpoS expression, although its participation in the regulation of lipid metabolism has not been analyzed. In this work we found that inactivation of psrA had no effect on the expression of β-oxidation genes in this bacterium, but instead decreased expression of the unsaturated fatty acid biosynthetic operon fabAB (3-hydroxydecanoyl-ACP dehydratase/isomerase and 3-ketoacyl-ACP synthase I). This inactivation also reduced the unsaturated fatty acid content, as revealed by the thin-layer chromatographic analysis, and confirmed by gas chromatography; notably, there was also a lower content of cyclopropane fatty acids, which are synthesized from unsaturated fatty acids. The absence of PsrA has no effect on the growth rate, but showed loss of cell viability during long-term growth, in accordance with the role of these unsaturated and cyclopropane fatty acids in the protection of membranes. Finally, an electrophoretic mobility shift assay revealed specific binding of PsrA to the fabA promoter region, where a putative binding site for this regulator was located. Taken together, our data show that PsrA plays an important role in the regulation of unsaturated fatty acids metabolism in A. vinelandii by positively regulating fabAB.
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Affiliation(s)
- Claudia Velázquez-Sánchez
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México
| | | | - Soledad Moreno
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México
| | - Raunel Tinoco-Valencia
- Departamento de Ingeniería Celular y Biocatálisis, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México
| | - Guadalupe Espín
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México
| | - Josefina Guzmán
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México
| | | | - Christian Sohlenkamp
- Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México
| | - Daniel Segura
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México.
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Aasfar A, Bargaz A, Yaakoubi K, Hilali A, Bennis I, Zeroual Y, Meftah Kadmiri I. Nitrogen Fixing Azotobacter Species as Potential Soil Biological Enhancers for Crop Nutrition and Yield Stability. Front Microbiol 2021; 12:628379. [PMID: 33717018 PMCID: PMC7947814 DOI: 10.3389/fmicb.2021.628379] [Citation(s) in RCA: 70] [Impact Index Per Article: 23.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2020] [Accepted: 02/05/2021] [Indexed: 12/20/2022] Open
Abstract
Biological nitrogen fixation (BNF) refers to a microbial mediated process based upon an enzymatic "Nitrogenase" conversion of atmospheric nitrogen (N2) into ammonium readily absorbable by roots. N2-fixing microorganisms collectively termed as "diazotrophs" are able to fix biologically N2 in association with plant roots. Specifically, the symbiotic rhizobacteria induce structural and physiological modifications of bacterial cells and plant roots into specialized structures called nodules. Other N2-fixing bacteria are free-living fixers that are highly diverse and globally widespread in cropland. They represent key natural source of nitrogen (N) in natural and agricultural ecosystems lacking symbiotic N fixation (SNF). In this review, the importance of Azotobacter species was highlighted as both important free-living N2-fixing bacteria and potential bacterial biofertilizer with proven efficacy for plant nutrition and biological soil fertility. In addition, we described Azotobacter beneficial plant promoting traits (e.g., nutrient use efficiency, protection against phytopathogens, phytohormone biosynthesis, etc.). We shed light also on the agronomic features of Azotobacter that are likely an effective component of integrated plant nutrition strategy, which contributes positively to sustainable agricultural production. We pointed out Azotobacter based-biofertilizers, which possess unique characteristics such as cyst formation conferring resistance to environmental stresses. Such beneficial traits can be explored profoundly for the utmost aim to research and develop specific formulations based on inoculant Azotobacter cysts. Furthermore, Azotobacter species still need to be wisely exploited in order to address specific agricultural challenges (e.g., nutrient deficiencies, biotic and abiotic constraints) taking into consideration several variables including their biological functions, synergies and multi-trophic interactions, and biogeography and abundance distribution.
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Affiliation(s)
- Abderrahim Aasfar
- Green Biotechnology Laboratory, Moroccan Foundation for Advanced Science, Innovation and Research (MAScIR), Rabat Design Centre, Rabat, Morocco.,Laboratory of Health Sciences and Technologies, High Institute of Health Sciences, Hassan 1st University, Settat, Morocco
| | - Adnane Bargaz
- AgroBioSciences-Microbiome, Laboratory of Plant-Microbe Interactions, Mohammed VI Polytechnic University, Ben Guerir, Morocco
| | - Kaoutar Yaakoubi
- Green Biotechnology Laboratory, Moroccan Foundation for Advanced Science, Innovation and Research (MAScIR), Rabat Design Centre, Rabat, Morocco
| | - Abderraouf Hilali
- Laboratory of Health Sciences and Technologies, High Institute of Health Sciences, Hassan 1st University, Settat, Morocco
| | - Iman Bennis
- Green Biotechnology Laboratory, Moroccan Foundation for Advanced Science, Innovation and Research (MAScIR), Rabat Design Centre, Rabat, Morocco
| | | | - Issam Meftah Kadmiri
- Green Biotechnology Laboratory, Moroccan Foundation for Advanced Science, Innovation and Research (MAScIR), Rabat Design Centre, Rabat, Morocco.,AgroBioSciences-Microbiome, Laboratory of Plant-Microbe Interactions, Mohammed VI Polytechnic University, Ben Guerir, Morocco
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