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Ortiz-Medina JF, Poole MR, Grunden AM, Call DF. Nitrogen Fixation and Ammonium Assimilation Pathway Expression of Geobacter sulfurreducens Changes in Response to the Anode Potential in Microbial Electrochemical Cells. Appl Environ Microbiol 2023; 89:e0207322. [PMID: 36975810 PMCID: PMC10132095 DOI: 10.1128/aem.02073-22] [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: 12/07/2022] [Accepted: 03/07/2023] [Indexed: 03/29/2023] Open
Abstract
Nitrogen gas (N2) fixation in the anode-respiring bacterium Geobacter sulfurreducens occurs through complex, multistep processes. Optimizing ammonium (NH4+) production from this bacterium in microbial electrochemical technologies (METs) requires an understanding of how those processes are regulated in response to electrical driving forces. In this study, we quantified gene expression levels (via RNA sequencing) of G. sulfurreducens growing on anodes fixed at two different potentials (-0.15 V and +0.15 V versus standard hydrogen electrode). The anode potential had a significant impact on the expression levels of N2 fixation genes. At -0.15 V, the expression of nitrogenase genes, such as nifH, nifD, and nifK, significantly increased relative to that at +0.15 V, as well as genes associated with NH4+ uptake and transformation, such as glutamine and glutamate synthetases. Metabolite analysis confirmed that both of these organic compounds were present in significantly higher intracellular concentrations at -0.15 V. N2 fixation rates (estimated using the acetylene reduction assay and normalized to total protein) were significantly larger at -0.15 V. Genes expressing flavin-based electron bifurcation complexes, such as electron-transferring flavoproteins (EtfAB) and the NADH-dependent ferredoxin:NADP reductase (NfnAB), were also significantly upregulated at -0.15 V, suggesting that these mechanisms may be involved in N2 fixation at that potential. Our results show that in energy-constrained situations (i.e., low anode potential), the cells increase per-cell respiration and N2 fixation rates. We hypothesize that at -0.15 V, they increase N2 fixation activity to help maintain redox homeostasis, and they leverage electron bifurcation as a strategy to optimize energy generation and use. IMPORTANCE Biological nitrogen fixation coupled with ammonium recovery provides a sustainable alternative to the carbon-, water-, and energy-intensive Haber-Bosch process. Aerobic biological nitrogen fixation technologies are hindered by oxygen gas inhibition of the nitrogenase enzyme. Electrically driving biological nitrogen fixation in anaerobic microbial electrochemical technologies overcomes this challenge. Using Geobacter sulfurreducens as a model exoelectrogenic diazotroph, we show that the anode potential in microbial electrochemical technologies has a significant impact on nitrogen gas fixation rates, ammonium assimilation pathways, and expression of genes associated with nitrogen gas fixation. These findings have important implications for understanding regulatory pathways of nitrogen gas fixation and will help identify target genes and operational strategies to enhance ammonium production in microbial electrochemical technologies.
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Affiliation(s)
- Juan F. Ortiz-Medina
- Department of Civil, Construction, and Environmental Engineering, North Carolina State University, Raleigh, North Carolina, USA
| | - Mark R. Poole
- Department of Civil, Construction, and Environmental Engineering, North Carolina State University, Raleigh, North Carolina, USA
| | - Amy M. Grunden
- Department of Plant and Microbial Biology, North Carolina State University, Raleigh, North Carolina, USA
| | - Douglas F. Call
- Department of Civil, Construction, and Environmental Engineering, North Carolina State University, Raleigh, North Carolina, USA
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Abstract
Inoculation of cereals with diazotrophic (N2-fixing) bacteria offers a sustainable alternative to the application of nitrogen fertilizers in agriculture. While natural diazotrophs have evolved multilayered regulatory mechanisms that couple N2 fixation with assimilation of the product NH3 and prevent release to plants, genetic modifications can permit excess production and excretion of NH3. However, a lack of stringent host-specificity for root colonization by the bacteria would allow growth promotion of target and nontarget plants species alike. Here, we exploit synthetic transkingdom signaling to establish plant host-specific control of the N2-fixation catalyst nitrogenase in Azorhizobium caulinodans occupying barley roots. This work demonstrates how partner-specific interactions can be established to avoid potential growth promotion of nontarget plants. Engineering N2-fixing symbioses between cereals and diazotrophic bacteria represents a promising strategy to sustainably deliver biologically fixed nitrogen (N) in agriculture. We previously developed novel transkingdom signaling between plants and bacteria, through plant production of the bacterial signal rhizopine, allowing control of bacterial gene expression in association with the plant. Here, we have developed both a homozygous rhizopine producing (RhiP) barley line and a hybrid rhizopine uptake system that conveys upon our model bacterium Azorhizobium caulinodans ORS571 (Ac) 103-fold improved sensitivity for rhizopine perception. Using this improved genetic circuitry, we established tight rhizopine-dependent transcriptional control of the nitrogenase master regulator nifA and the N metabolism σ-factor rpoN, which drove nitrogenase expression and activity in vitro and in situ by bacteria colonizing RhiP barley roots. Although in situ nitrogenase activity was suboptimally effective relative to the wild-type strain, activation was specific to RhiP barley and was not observed on the roots of wild-type plants. This work represents a key milestone toward the development of a synthetic plant-controlled symbiosis in which the bacteria fix N2 only when in contact with the desired host plant and are prevented from interaction with nontarget plant species.
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RNA-Seq Provides New Insights into the Gene Expression Changes in Azoarcus olearius BH72 under Nitrogen-Deficient and Replete Conditions beyond the Nitrogen Fixation Process. Microorganisms 2021; 9:microorganisms9091888. [PMID: 34576783 PMCID: PMC8467165 DOI: 10.3390/microorganisms9091888] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2021] [Revised: 08/26/2021] [Accepted: 08/30/2021] [Indexed: 11/17/2022] Open
Abstract
Azoarcus olearius BH72 is an endophyte capable of biological nitrogen fixation (BNF) and of supplying nitrogen to its host plant. Our previous microarray approach provided insights into the transcriptome of strain BH72 under N2-fixation in comparison to ammonium-grown conditions, which already indicated the induction of genes not related to the BNF process. Due to the known limitations of the technique, we might have missed additional differentially expressed genes (DEGs). Thus, we used directional RNA-Seq to better comprehend the transcriptional landscape under these growth conditions. RNA-Seq detected almost 24% of the annotated genes to be regulated, twice the amount identified by microarray. In addition to confirming entire regulated operons containing known DEGs, the new approach detected the induction of genes involved in carbon metabolism and flagellar and twitching motility. This may support N2-fixation by increasing energy production and by finding suitable microaerobic niches. On the other hand, energy expenditures were reduced by suppressing translation and vitamin biosynthesis. Nonetheless, strain BH72 does not appear to be content with N2-fixation but is primed for alternative economic N-sources, such as nitrate, urea or amino acids; a strong gene induction of machineries for their uptake and assimilation was detected. RNA-Seq has thus provided a better understanding of a lifestyle under limiting nitrogen sources by elucidating hitherto unknown regulated processes.
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North JA, Narrowe AB, Xiong W, Byerly KM, Zhao G, Young SJ, Murali S, Wildenthal JA, Cannon WR, Wrighton KC, Hettich RL, Tabita FR. A nitrogenase-like enzyme system catalyzes methionine, ethylene, and methane biogenesis. Science 2020; 369:1094-1098. [PMID: 32855335 DOI: 10.1126/science.abb6310] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2020] [Accepted: 06/12/2020] [Indexed: 12/16/2022]
Abstract
Bacterial production of gaseous hydrocarbons such as ethylene and methane affects soil environments and atmospheric climate. We demonstrate that biogenic methane and ethylene from terrestrial and freshwater bacteria are directly produced by a previously unknown methionine biosynthesis pathway. This pathway, present in numerous species, uses a nitrogenase-like reductase that is distinct from known nitrogenases and nitrogenase-like reductases and specifically functions in C-S bond breakage to reduce ubiquitous and appreciable volatile organic sulfur compounds such as dimethyl sulfide and (2-methylthio)ethanol. Liberated methanethiol serves as the immediate precursor to methionine, while ethylene or methane is released into the environment. Anaerobic ethylene production by this pathway apparently explains the long-standing observation of ethylene accumulation in oxygen-depleted soils. Methane production reveals an additional bacterial pathway distinct from archaeal methanogenesis.
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Affiliation(s)
- Justin A North
- Department of Microbiology, The Ohio State University, Columbus, OH 43210, USA
| | - Adrienne B Narrowe
- Department of Soil and Crop Sciences, Colorado State University, Fort Collins, CO 80523, USA
| | - Weili Xiong
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA
| | - Kathryn M Byerly
- Department of Microbiology, The Ohio State University, Columbus, OH 43210, USA
| | - Guanqi Zhao
- Department of Microbiology, The Ohio State University, Columbus, OH 43210, USA
| | - Sarah J Young
- Department of Microbiology, The Ohio State University, Columbus, OH 43210, USA
| | - Srividya Murali
- Department of Microbiology, The Ohio State University, Columbus, OH 43210, USA
| | - John A Wildenthal
- Department of Microbiology, The Ohio State University, Columbus, OH 43210, USA
| | - William R Cannon
- Pacific Northwest National Laboratory, Richland, WA 99352, USA.,Department of Mathematics, University of California, Riverside, Riverside, CA 92507, USA
| | - Kelly C Wrighton
- Department of Soil and Crop Sciences, Colorado State University, Fort Collins, CO 80523, USA
| | - Robert L Hettich
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA
| | - F Robert Tabita
- Department of Microbiology, The Ohio State University, Columbus, OH 43210, USA.
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Fernandez L, Peura S, Eiler A, Linz AM, McMahon KD, Bertilsson S. Diazotroph Genomes and Their Seasonal Dynamics in a Stratified Humic Bog Lake. Front Microbiol 2020; 11:1500. [PMID: 32714313 PMCID: PMC7341956 DOI: 10.3389/fmicb.2020.01500] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Accepted: 06/09/2020] [Indexed: 12/28/2022] Open
Abstract
Aquatic N-fixation is generally associated with the growth and mass development of Cyanobacteria in nitrogen-deprived photic zones. However, sequenced genomes and environmental surveys suggest active aquatic N-fixation also by many non-cyanobacterial groups. Here, we revealed the seasonal variation and genomic diversity of potential N-fixers in a humic bog lake using metagenomic data and nif gene clusters analysis. Groups with diazotrophic operons were functionally divergent and included Cholorobi, Geobacter, Desulfobacterales, Methylococcales, and Acidobacteria. In addition to nifH (a gene that encodes the dinitrogenase reductase component of the molybdenum nitrogenase), we also identified sequences corresponding to vanadium and iron-only nitrogenase genes. Within the Chlorobi population, the nitrogenase (nifH) cluster was included in a well-structured retrotransposon. Furthermore, the presence of light-harvesting photosynthesis genes implies that anoxygenic photosynthesis may fuel nitrogen fixation under the prevailing low-irradiance conditions. The presence of rnf genes (related to the expression of H+/Na+-translocating ferredoxin: NAD+ oxidoreductase) in Methylococcales and Desulfobacterales suggests that other energy-generating processes may drive the costly N-fixation in the absence of photosynthesis. The highly reducing environment of the anoxic bottom layer of Trout Bog Lake may thus also provide a suitable niche for active N-fixers and primary producers. While future studies on the activity of these potential N-fixers are needed to clarify their role in freshwater nitrogen cycling, the metagenomic data presented here enabled an initial characterization of previously overlooked diazotrophs in freshwater biomes.
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Affiliation(s)
- Leyden Fernandez
- Department of Ecology and Genetics, Limnology and Science for Life Laboratory, Uppsala University, Uppsala, Sweden
| | - Sari Peura
- Department of Forest Mycology and Plant Pathology, Science for Life Laboratory, Swedish University of Agricultural Sciences, Uppsala, Sweden
| | - Alexander Eiler
- Department of Ecology and Genetics, Limnology and Science for Life Laboratory, Uppsala University, Uppsala, Sweden
- Centre for Biogeochemistry in the Anthropocene, Department of Biosciences, Section for Aquatic Biology and Toxicology, University of Oslo, Oslo, Norway
| | - Alexandra M. Linz
- Great Lakes Bioenergy Research Center, Wisconsin Energy Institute, University of Wisconsin–Madison, Madison, WI, United States
| | - Katherine D. McMahon
- Department of Bacteriology, University of Wisconsin–Madison, Madison, WI, United States
- Department of Civil and Environmental Engineering, University of Wisconsin–Madison, Madison, WI, United States
| | - Stefan Bertilsson
- Department of Ecology and Genetics, Limnology and Science for Life Laboratory, Uppsala University, Uppsala, Sweden
- Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden
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Nag P, Shriti S, Das S. Microbiological strategies for enhancing biological nitrogen fixation in nonlegumes. J Appl Microbiol 2020; 129:186-198. [PMID: 31858682 DOI: 10.1111/jam.14557] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2019] [Revised: 12/12/2019] [Accepted: 12/16/2019] [Indexed: 01/17/2023]
Abstract
In an agro-ecosystem, industrially produced nitrogenous fertilizers are the principal sources of nitrogen for plant growth; unfortunately these also serve as the leading sources of pollution. Hence, it becomes imperative to find pollution-free methods of providing nitrogen to crop plants. A diverse group of free-living, plant associative and symbiotic prokaryotes are able to perform biological nitrogen fixation (BNF). BNF is a two component process involving the nitrogen fixing diazotrophs and the host plant. Symbiotic nitrogen fixation is most efficient as it can fix nitrogen inside the nodule formed on the roots of the plant; delivering nitrogen directly to the host. However, most of the important crop plants are nonleguminous and are unable to form symbiotic associations. In this context, the plant associative and endophytic diazotrophs assume importance. BNF in nonlegumes can be encouraged either through the transfer of BNF traits from legumes or by elevating the nitrogen fixing capacity of the associative and endophytic diazotrophs. In this review we discuss mainly the microbiological strategies which may be used in nonleguminous crops for enhancement of BNF.
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Affiliation(s)
- P Nag
- Division of Plant Biology, Bose Institute, Kolkata, West Bengal, India
| | - S Shriti
- Division of Plant Biology, Bose Institute, Kolkata, West Bengal, India
| | - S Das
- Division of Plant Biology, Bose Institute, Kolkata, West Bengal, India
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Tan Y, Xu Z, Tao J, Ni J, Zhao W, Lu J, Yao YF. A SIRT4-like auto ADP-ribosyltransferase is essential for the environmental growth of Mycobacterium smegmatis. Acta Biochim Biophys Sin (Shanghai) 2016; 48:145-52. [PMID: 26685303 DOI: 10.1093/abbs/gmv121] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2015] [Accepted: 09/26/2015] [Indexed: 01/12/2023] Open
Abstract
SIRT family proteins are highly conserved both in the structure and function among all the organisms, and are involved in gene silencing, DNA damage repair, cell growth and metabolism. Here, a SIRT4 homologue MSMEG_4620 was identified and characterized in Mycobacterium smegmatis. MSMEG_4620 exhibits deacetylase activity that can be activated by fatty acids. Interestingly, MSMEG_4620 also possesses auto ADP-ribosylation activity. MSMEG_4620 is modified on arginine residues as revealed by a chemical stability assay. Moreover, the auto ADP-ribosylation activity of MSMEG_4620 was found to be enhanced by ferric ion. Notably, the SIRT4 homologues are widely distributed in the genomes of environmental mycobacterial species instead of pathogenic mycobacterial species. When MSMEG_4620 was deleted in M. smegmatis, the mutant strain showed a growth defect in 7H9 minimal medium compared with the parental strain. Taken together, these results provided the characteristics of a SIRT4 homologue in prokaryotes and implicated its critical roles in the growth of environmental mycobacterial species.
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Affiliation(s)
- Yongcong Tan
- Laboratory of Bacterial Pathogenesis, Department of Microbiology and Immunology, Institutes of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Zhihong Xu
- Laboratory of Bacterial Pathogenesis, Department of Microbiology and Immunology, Institutes of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Jing Tao
- Laboratory of Bacterial Pathogenesis, Department of Microbiology and Immunology, Institutes of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Jinjing Ni
- Laboratory of Bacterial Pathogenesis, Department of Microbiology and Immunology, Institutes of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Wei Zhao
- Laboratory of Synthetic Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China
| | - Jie Lu
- Department of Infectious Diseases, Shanghai Ruijin Hospital, Shanghai 200025, China
| | - Yu-Feng Yao
- Laboratory of Bacterial Pathogenesis, Department of Microbiology and Immunology, Institutes of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
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Huergo LF, Chandra G, Merrick M. PIIsignal transduction proteins: nitrogen regulation and beyond. FEMS Microbiol Rev 2013; 37:251-83. [DOI: 10.1111/j.1574-6976.2012.00351.x] [Citation(s) in RCA: 141] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2012] [Revised: 07/26/2012] [Accepted: 07/26/2012] [Indexed: 01/12/2023] Open
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Huergo LF, Pedrosa FO, Muller-Santos M, Chubatsu LS, Monteiro RA, Merrick M, Souza EM. PII signal transduction proteins: pivotal players in post-translational control of nitrogenase activity. MICROBIOLOGY-SGM 2012; 158:176-190. [PMID: 22210804 DOI: 10.1099/mic.0.049783-0] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The fixation of atmospheric nitrogen by the prokaryotic enzyme nitrogenase is an energy- expensive process and consequently it is tightly regulated at a variety of levels. In many diazotrophs this includes post-translational regulation of the enzyme's activity, which has been reported in both bacteria and archaea. The best understood response is the short-term inactivation of nitrogenase in response to a transient rise in ammonium levels in the environment. A number of proteobacteria species effect this regulation through reversible ADP-ribosylation of the enzyme, but other prokaryotes have evolved different mechanisms. Here we review current knowledge of post-translational control of nitrogenase and show that, for the response to ammonium, the P(II) signal transduction proteins act as key players.
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Affiliation(s)
- Luciano F Huergo
- Instituto Nacional de Ciência e Tecnologia da Fixação Biológica de Nitrogênio, Departamento de Bioquímica e Biologia Molecular, UFPR Curitiba, PR, Brazil
| | - Fábio O Pedrosa
- Instituto Nacional de Ciência e Tecnologia da Fixação Biológica de Nitrogênio, Departamento de Bioquímica e Biologia Molecular, UFPR Curitiba, PR, Brazil
| | - Marcelo Muller-Santos
- Instituto Nacional de Ciência e Tecnologia da Fixação Biológica de Nitrogênio, Departamento de Bioquímica e Biologia Molecular, UFPR Curitiba, PR, Brazil
| | - Leda S Chubatsu
- Instituto Nacional de Ciência e Tecnologia da Fixação Biológica de Nitrogênio, Departamento de Bioquímica e Biologia Molecular, UFPR Curitiba, PR, Brazil
| | - Rose A Monteiro
- Instituto Nacional de Ciência e Tecnologia da Fixação Biológica de Nitrogênio, Departamento de Bioquímica e Biologia Molecular, UFPR Curitiba, PR, Brazil
| | - Mike Merrick
- Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, UK
| | - Emanuel M Souza
- Instituto Nacional de Ciência e Tecnologia da Fixação Biológica de Nitrogênio, Departamento de Bioquímica e Biologia Molecular, UFPR Curitiba, PR, Brazil
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Sarkar A, Köhler J, Hurek T, Reinhold-Hurek B. A novel regulatory role of the Rnf complex of Azoarcus sp. strain BH72. Mol Microbiol 2011; 83:408-22. [DOI: 10.1111/j.1365-2958.2011.07940.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Oetjen J, Rexroth S, Reinhold-Hurek B. Mass spectrometric characterization of the covalent modification of the nitrogenase Fe-protein in Azoarcus sp. BH72. FEBS J 2009; 276:3618-27. [PMID: 19490119 DOI: 10.1111/j.1742-4658.2009.07081.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Nitrogenase Fe-protein modification was analyzed in the endophytic beta-proteobacterium Azoarcus sp. BH72. Application of modern MS techniques localized the modification in the peptide sequence and revealed it to be an ADP-ribosylation on Arg102 of one subunit of nitrogenase Fe-protein. A double digest with trypsin and endoproteinase Asp-N was necessary to obtain an analyzable peptide because the modification blocked the trypsin cleavage site at this residue. Furthermore, a peptide extraction protocol without trifluoroacetic acid was crucial to acquire the modified peptide, indicating an acid lability of the ADP-ribosylation. This finding was supported by the presence of a truncated version of the original peptide with Arg102 exchanged by ornithine. Site-directed mutagenesis verified that the ADP-ribosylation occurred on Arg102. With our approach, we were able to localize a labile modification within a large peptide of 31 amino acid residues. The present study provides a method suitable for the identification of so far unknown protein modifications on nitrogenases or other proteins. It represents a new tool for the MS analysis of protein mono-ADP-ribosylations.
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Affiliation(s)
- Janina Oetjen
- General Microbiology, Faculty of Biology and Chemistry, University Bremen, Germany
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