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Willard D, Arellano JJ, Underdahl M, Lee TM, Ramaswamy AS, Fumes G, Kliman A, Wong EY, Owens CP. Mutational Analysis of the Nitrogenase Carbon Monoxide Protective Protein CowN Reveals That a Conserved C-Terminal Glutamic Acid Residue Is Necessary for Its Activity. Biochemistry 2024; 63:152-158. [PMID: 38091601 PMCID: PMC10765410 DOI: 10.1021/acs.biochem.3c00421] [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: 08/10/2023] [Revised: 11/21/2023] [Accepted: 11/27/2023] [Indexed: 01/03/2024]
Abstract
Nitrogenase is the only enzyme that catalyzes the reduction of nitrogen gas into ammonia. Nitrogenase is tightly inhibited by the environmental gas carbon monoxide (CO). Many nitrogen fixing bacteria protect nitrogenase from CO inhibition using the protective protein CowN. This work demonstrates that a conserved glutamic acid residue near the C-terminus of Gluconacetobacter diazotrophicus CowN is necessary for its function. Mutation of the glutamic acid residue abolishes both CowN's protection against CO inhibition and the ability of CowN to bind to nitrogenase. In contrast, a conserved C-terminal cysteine residue is not important for CO protection by CowN. Overall, this work uncovers structural features in CowN that are required for its function and provides new insights into its nitrogenase binding and CO protection mechanism.
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Affiliation(s)
- Dustin
L. Willard
- Department of Chemistry and
Biochemistry, Schmid College, Chapman University, Orange, California 92866, United States
| | - Joshuah J. Arellano
- Department of Chemistry and
Biochemistry, Schmid College, Chapman University, Orange, California 92866, United States
| | - Mitch Underdahl
- Department of Chemistry and
Biochemistry, Schmid College, Chapman University, Orange, California 92866, United States
| | - Terrence M. Lee
- Department of Chemistry and
Biochemistry, Schmid College, Chapman University, Orange, California 92866, United States
| | - Avinash S. Ramaswamy
- Department of Chemistry and
Biochemistry, Schmid College, Chapman University, Orange, California 92866, United States
| | - Gabriella Fumes
- Department of Chemistry and
Biochemistry, Schmid College, Chapman University, Orange, California 92866, United States
| | - Agatha Kliman
- Department of Chemistry and
Biochemistry, Schmid College, Chapman University, Orange, California 92866, United States
| | - Emily Y. Wong
- Department of Chemistry and
Biochemistry, Schmid College, Chapman University, Orange, California 92866, United States
| | - Cedric P. Owens
- Department of Chemistry and
Biochemistry, Schmid College, Chapman University, Orange, California 92866, United States
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2
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Kang B, Lee H, Oh S, Kim JY, Ko YJ, Chang IS. Regulatory transcription factor (CooA)-driven carbon monoxide partial pressure sensing whole-cell biosensor. Heliyon 2023; 9:e17391. [PMID: 37408883 PMCID: PMC10318455 DOI: 10.1016/j.heliyon.2023.e17391] [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] [Received: 05/26/2023] [Revised: 06/12/2023] [Accepted: 06/15/2023] [Indexed: 07/07/2023] Open
Abstract
We designed and constructed a whole-cell biosensor capable of detecting the presence and quantity of carbon monoxide (CO) using the CO regulatory transcription factor. This biosensor utilizes CooA, a CO-sensing transcription regulator that activates the expression of carbon monoxide dehydrogenase (CODH), to detect the presence of CO and respond by triggering the expression of a GUS reporter protein (β-glucuronidase). The GUS reporter protein is expressed from a CO-induced CooA-binding promoter (PcooF) by CooA and enables the effective colorimetric detection of CO. An Escherichia coli strain used to validate the biosensor showed growth and GUS activity under anaerobic conditions; this study used the inert gas (Ar) to create anaerobic conditions. The pBRCO biosensor could successfully detect the presence of CO in the headspace. Moreover, the GUS-specific activity of pBRCO according to the CO strength as partial pressure followed Michaelis-Menten kinetics (R2 = 0.98). It was confirmed that the GUS-specific activity of pBRCO increased linearly up to 30.39 kPa (R2 = 0.98), and thus, a quantitative analysis of CO concentration (i.e., partial pressure) was possible.
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Affiliation(s)
- Byeongchan Kang
- School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, Republic of Korea
| | - Hyeryeong Lee
- School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, Republic of Korea
- Research Center for Innovative Energy and Carbon Optimized Synthesis for Chemicals (inn-ECOSysChem), Gwangju Institute of Science and Technology, Gwangju 61005, Republic of Korea
| | - Soyoung Oh
- School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, Republic of Korea
| | - Ji-Yeon Kim
- School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, Republic of Korea
- Research Center for Innovative Energy and Carbon Optimized Synthesis for Chemicals (inn-ECOSysChem), Gwangju Institute of Science and Technology, Gwangju 61005, Republic of Korea
| | - Young-Joon Ko
- School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, Republic of Korea
| | - In Seop Chang
- School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, Republic of Korea
- Research Center for Innovative Energy and Carbon Optimized Synthesis for Chemicals (inn-ECOSysChem), Gwangju Institute of Science and Technology, Gwangju 61005, Republic of Korea
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3
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Dent MR, Weaver BR, Roberts MG, Burstyn JN. Carbon Monoxide-Sensing Transcription Factors: Regulators of Microbial Carbon Monoxide Oxidation Pathway Gene Expression. J Bacteriol 2023; 205:e0033222. [PMID: 37154694 PMCID: PMC10210986 DOI: 10.1128/jb.00332-22] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/10/2023] Open
Abstract
Carbon monoxide (CO) serves as a source of energy and carbon for a diverse set of microbes found in anaerobic and aerobic environments. The enzymes that bacteria and archaea use to oxidize CO depend upon complex metallocofactors that require accessory proteins for assembly and proper function. This complexity comes at a high energetic cost and necessitates strict regulation of CO metabolic pathways in facultative CO metabolizers to ensure that gene expression occurs only when CO concentrations and redox conditions are appropriate. In this review, we examine two known heme-dependent transcription factors, CooA and RcoM, that regulate inducible CO metabolism pathways in anaerobic and aerobic microorganisms. We provide an analysis of the known physiological and genomic contexts of these sensors and employ this analysis to contextualize known biochemical properties. In addition, we describe a growing list of putative transcription factors associated with CO metabolism that potentially use cofactors other than heme to sense CO.
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Affiliation(s)
- Matthew R. Dent
- Heart, Lung, Blood, and Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Brian R. Weaver
- Department of Chemistry, University of Wisconsin–Madison, Madison, Wisconsin, USA
| | - Madeleine G. Roberts
- Department of Chemistry, University of Wisconsin–Madison, Madison, Wisconsin, USA
| | - Judith N. Burstyn
- Department of Chemistry, University of Wisconsin–Madison, Madison, Wisconsin, USA
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Dent MR, Roberts MG, Bowman HE, Weaver BR, McCaslin DR, Burstyn JN. Quaternary Structure and Deoxyribonucleic Acid-Binding Properties of the Heme-Dependent, CO-Sensing Transcriptional Regulator PxRcoM. Biochemistry 2022; 61:678-688. [PMID: 35394749 PMCID: PMC11155679 DOI: 10.1021/acs.biochem.2c00086] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
RcoM, a heme-containing, CO-sensing transcription factor, is one of two known bacterial regulators of CO metabolism. Unlike its analogue CooA, the structure and DNA-binding properties of RcoM remain largely uncharacterized. Using a combination of size exclusion chromatography and sedimentation equilibrium, we demonstrate that RcoM-1 from Paraburkholderia xenovorans is a dimer, wherein the heme-binding domain mediates dimerization. Using bioinformatics, we show that RcoM is found in three distinct genomic contexts, in accordance with the previous literature. We propose a refined consensus DNA-binding sequence for RcoM based on sequence alignments of coxM-associated promoters. The RcoM promoter consensus sequence bears two well-conserved direct repeats, consistent with other LytTR domain-containing transcription factors. In addition, there is a third, moderately conserved direct repeat site. Surprisingly, PxRcoM-1 requires all three repeat sites to cooperatively bind DNA with a [P]1/2 of 250 ± 10 nM and an average Hill coefficient, n, of 1.7 ± 0.1. The paralog PxRcoM-2 binds to the same triplet motif with comparable affinity and cooperativity. Considering this unusual DNA binding stoichiometry, that is, a dimeric protein with a triplet DNA repeat-binding site, we hypothesize that RcoM interacts with DNA in a manner distinct from other LytTR domain-containing transcription factors.
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Affiliation(s)
- Matthew R Dent
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Madeleine G Roberts
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Hannah E Bowman
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Brian R Weaver
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Darrell R McCaslin
- Biophysics Instrumentation Facility, Department of Biochemistry, University of Wisconsin-Madison, 433 Babcock Drive, Madison, Wisconsin 53706, United States
| | - Judith N Burstyn
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
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5
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Oehlmann NN, Rebelein JG. The Conversion of Carbon Monoxide and Carbon Dioxide by Nitrogenases. Chembiochem 2021; 23:e202100453. [PMID: 34643977 PMCID: PMC9298215 DOI: 10.1002/cbic.202100453] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2021] [Revised: 10/13/2021] [Indexed: 12/02/2022]
Abstract
Nitrogenases are the only known family of enzymes that catalyze the reduction of molecular nitrogen (N2) to ammonia (NH3). The N2 reduction drives biological nitrogen fixation and the global nitrogen cycle. Besides the conversion of N2, nitrogenases catalyze a whole range of other reductions, including the reduction of the small gaseous substrates carbon monoxide (CO) and carbon dioxide (CO2) to hydrocarbons. However, it remains an open question whether these ‘side reactivities’ play a role under environmental conditions. Nonetheless, these reactivities and particularly the formation of hydrocarbons have spurred the interest in nitrogenases for biotechnological applications. There are three different isozymes of nitrogenase: the molybdenum and the alternative vanadium and iron‐only nitrogenase. The isozymes differ in their metal content, structure, and substrate‐dependent activity, despite their homology. This minireview focuses on the conversion of CO and CO2 to methane and higher hydrocarbons and aims to specify the differences in activity between the three nitrogenase isozymes.
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Affiliation(s)
- Niels N Oehlmann
- Max Planck Institute for Terrestrial Microbiology, Karl-von-Frisch-Straße 10, 35043, Marburg, Germany
| | - Johannes G Rebelein
- Max Planck Institute for Terrestrial Microbiology, Karl-von-Frisch-Straße 10, 35043, Marburg, Germany
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6
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Medina MS, Bretzing KO, Aviles RA, Chong KM, Espinoza A, Garcia CNG, Katz BB, Kharwa RN, Hernandez A, Lee JL, Lee TM, Lo Verde C, Strul MW, Wong EY, Owens CP. CowN sustains nitrogenase turnover in the presence of the inhibitor carbon monoxide. J Biol Chem 2021; 296:100501. [PMID: 33667548 PMCID: PMC8047169 DOI: 10.1016/j.jbc.2021.100501] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2020] [Revised: 01/28/2021] [Accepted: 03/01/2021] [Indexed: 11/28/2022] Open
Abstract
Nitrogenase is the only enzyme capable of catalyzing nitrogen fixation, the reduction of dinitrogen gas (N2) to ammonia (NH3). Nitrogenase is tightly inhibited by the environmental gas carbon monoxide (CO). Nitrogen-fixing bacteria rely on the protein CowN to grow in the presence of CO. However, the mechanism by which CowN operates is unknown. Here, we present the biochemical characterization of CowN and examine how CowN protects nitrogenase from CO. We determine that CowN interacts directly with nitrogenase and that CowN protection observes hyperbolic kinetics with respect to CowN concentration. At a CO concentration of 0.001 atm, CowN restores nearly full nitrogenase activity. Our results further indicate that CowN's protection mechanism involves decreasing the binding affinity of CO to nitrogenase's active site approximately tenfold without interrupting substrate turnover. Taken together, our work suggests CowN is an important auxiliary protein in nitrogen fixation that engenders CO tolerance to nitrogenase.
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Affiliation(s)
- Michael S Medina
- Schmid College of Science and Technology, Chapman University, Orange, California, USA
| | - Kevin O Bretzing
- Schmid College of Science and Technology, Chapman University, Orange, California, USA
| | - Richard A Aviles
- Schmid College of Science and Technology, Chapman University, Orange, California, USA
| | - Kiersten M Chong
- Schmid College of Science and Technology, Chapman University, Orange, California, USA
| | - Alejandro Espinoza
- Schmid College of Science and Technology, Chapman University, Orange, California, USA
| | - Chloe Nicole G Garcia
- Schmid College of Science and Technology, Chapman University, Orange, California, USA
| | - Benjamin B Katz
- Department of Chemistry, University of California, Irvine, Irvine, California, USA
| | - Ruchita N Kharwa
- Schmid College of Science and Technology, Chapman University, Orange, California, USA
| | - Andrea Hernandez
- Schmid College of Science and Technology, Chapman University, Orange, California, USA
| | - Justin L Lee
- Department of Chemistry, University of California, Irvine, Irvine, California, USA
| | - Terrence M Lee
- Schmid College of Science and Technology, Chapman University, Orange, California, USA
| | - Christine Lo Verde
- Schmid College of Science and Technology, Chapman University, Orange, California, USA
| | - Max W Strul
- Schmid College of Science and Technology, Chapman University, Orange, California, USA
| | - Emily Y Wong
- Schmid College of Science and Technology, Chapman University, Orange, California, USA
| | - Cedric P Owens
- Schmid College of Science and Technology, Chapman University, Orange, California, USA.
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7
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Hopper CP, De La Cruz LK, Lyles KV, Wareham LK, Gilbert JA, Eichenbaum Z, Magierowski M, Poole RK, Wollborn J, Wang B. Role of Carbon Monoxide in Host-Gut Microbiome Communication. Chem Rev 2020; 120:13273-13311. [PMID: 33089988 DOI: 10.1021/acs.chemrev.0c00586] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Nature is full of examples of symbiotic relationships. The critical symbiotic relation between host and mutualistic bacteria is attracting increasing attention to the degree that the gut microbiome is proposed by some as a new organ system. The microbiome exerts its systemic effect through a diverse range of metabolites, which include gaseous molecules such as H2, CO2, NH3, CH4, NO, H2S, and CO. In turn, the human host can influence the microbiome through these gaseous molecules as well in a reciprocal manner. Among these gaseous molecules, NO, H2S, and CO occupy a special place because of their widely known physiological functions in the host and their overlap and similarity in both targets and functions. The roles that NO and H2S play have been extensively examined by others. Herein, the roles of CO in host-gut microbiome communication are examined through a discussion of (1) host production and function of CO, (2) available CO donors as research tools, (3) CO production from diet and bacterial sources, (4) effect of CO on bacteria including CO sensing, and (5) gut microbiome production of CO. There is a large amount of literature suggesting the "messenger" role of CO in host-gut microbiome communication. However, much more work is needed to begin achieving a systematic understanding of this issue.
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Affiliation(s)
- Christopher P Hopper
- Institute for Experimental Biomedicine, University Hospital Wuerzburg, Wuerzburg, Bavaria DE 97080, Germany.,Department of Medicinal Chemistry, College of Pharmacy, The University of Florida, Gainesville, Florida 32611, United States
| | - Ladie Kimberly De La Cruz
- Department of Chemistry & Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, Georgia 30303, United States
| | - Kristin V Lyles
- Department of Biology, Georgia State University, Atlanta, Georgia 30303, United States
| | - Lauren K Wareham
- The Vanderbilt Eye Institute and Department of Ophthalmology & Visual Sciences, The Vanderbilt University Medical Center and School of Medicine, Nashville, Tennessee 37232, United States
| | - Jack A Gilbert
- Department of Pediatrics, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093, United States
| | - Zehava Eichenbaum
- Department of Biology, Georgia State University, Atlanta, Georgia 30303, United States
| | - Marcin Magierowski
- Cellular Engineering and Isotope Diagnostics Laboratory, Department of Physiology, Jagiellonian University Medical College, Cracow PL 31-531, Poland
| | - Robert K Poole
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Firth Court, Sheffield S10 2TN, U.K
| | - Jakob Wollborn
- Department of Anesthesiology and Critical Care, Medical Center, University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg DE 79085, Germany.,Department of Anesthesiology, Perioperative and Pain Management, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, United States
| | - Binghe Wang
- Department of Chemistry & Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, Georgia 30303, United States
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8
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Two-Stage Continuous Conversion of Carbon Monoxide to Ethylene by Whole Cells of Azotobacter vinelandii. Appl Environ Microbiol 2020; 86:AEM.00446-20. [PMID: 32198172 DOI: 10.1128/aem.00446-20] [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: 02/20/2020] [Accepted: 03/17/2020] [Indexed: 01/17/2023] Open
Abstract
Azotobacter vinelandii is an obligate aerobic diazotroph with a verified transient ability to reduce carbon monoxide to ethylene by its vanadium nitrogenase. In this study, we implemented an industrially relevant continuous two-stage stirred-tank system for in vivo biotransformation of a controlled supply of air enriched with 5% carbon monoxide to 302 μg ethylene g-1 glucose consumed. To attain this value, the process required overcoming critical oxygen limitations during cell proliferation while simultaneously avoiding the A. vinelandii respiratory protection mechanism that negatively impacts in vivo nitrogenase activity. Additionally, process conditions allowed the demonstration of carbon monoxide's solubility as a reaction-limiting factor and a competitor with dinitrogen for the vanadium nitrogenase active site, implying that excess intracellular carbon monoxide could lead to a cessation of cell proliferation and ethylene formation as shown genetically using a new strain of A. vinelandii deficient in carbon monoxide dehydrogenase.IMPORTANCE Ethylene is an essential commodity feedstock used for the generation of a variety of consumer products, but its generation demands energy-intensive processes and is dependent on nonrenewable substrates. This work describes a continuous biological method for investigating the nitrogenase-mediated carbon monoxide reductive coupling involved in ethylene production using whole cells of Azotobacter vinelandii If eventually adopted by industry, this technology has the potential to significantly reduce the total energy input required and the ethylene recovery costs, as well as decreasing greenhouse gas emissions associated with current production strategies.
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9
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Ainala SK, Seol E, Kim JR, Park S. Citrobacter amalonaticus Y19 for constitutive expression of carbon monoxide-dependent hydrogen-production machinery. BIOTECHNOLOGY FOR BIOFUELS 2017; 10:80. [PMID: 28360938 PMCID: PMC5371261 DOI: 10.1186/s13068-017-0770-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/30/2016] [Accepted: 03/22/2017] [Indexed: 06/07/2023]
Abstract
BACKGROUND Citrobacter amalonaticus Y19 is a good biocatalyst for production of hydrogen (H2) from oxidation of carbon monoxide (CO) via the so-called water-gas-shift reaction (WGSR). It has a high H2-production activity (23.83 mmol H2 g-1 cell h-1) from CO, and can grow well to a high density on various sugars. However, its H2-production activity is expressed only when CO is present as an inducer and in the absence of glucose. RESULTS In order to avoid dependency on CO and glucose, in the present study, the native CO-inducible promoters of WGSR operons (CO dehydrogenase, CODH, and CODH-dependent hydrogenase, CO-hyd) in Y19 were carefully analyzed and replaced with strong and constitutive promoters screened from Y19. One engineered strain (Y19-PR1), selected from three positive ones after screening ~10,000 colonies, showed a similar CO-dependent H2-production activity to that of wild-type Y19, without being affected by glucose and/or CO. Compared with wild-type Y19, transcription of the CODH operon in Y19-PR1 increased 1.5-fold, although that of the CO-hyd operon remained at a similar level. To enhance the activity of CO-Hyd in Y19-PR1, further modifications, including an increase in gene copy number and engineering of the 5' untranslated region, were attempted, but without success. CONCLUSIONS Convenient recombinant Y19-PR1 that expresses CO-dependent H2-production activity without being limited by CO and glucose was obtained.
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Affiliation(s)
- Satish Kumar Ainala
- School of Chemical and Biomolecular Engineering, Pusan National University, San 30, Jangeon-dong, Geumjeong-gu, Busan, 609-735 Republic of Korea
| | - Eunhee Seol
- School of Chemical and Biomolecular Engineering, Pusan National University, San 30, Jangeon-dong, Geumjeong-gu, Busan, 609-735 Republic of Korea
| | - Jung Rae Kim
- School of Chemical and Biomolecular Engineering, Pusan National University, San 30, Jangeon-dong, Geumjeong-gu, Busan, 609-735 Republic of Korea
| | - Sunghoon Park
- School of Chemical and Biomolecular Engineering, Pusan National University, San 30, Jangeon-dong, Geumjeong-gu, Busan, 609-735 Republic of Korea
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10
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Proteome Profiling of the Rhodobacter capsulatus Molybdenum Response Reveals a Role of IscN in Nitrogen Fixation by Fe-Nitrogenase. J Bacteriol 2015; 198:633-43. [PMID: 26644433 DOI: 10.1128/jb.00750-15] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2015] [Accepted: 11/12/2015] [Indexed: 01/11/2023] Open
Abstract
UNLABELLED Rhodobacter capsulatus is capable of synthesizing two nitrogenases, a molybdenum-dependent nitrogenase and an alternative Mo-free iron-only nitrogenase, enabling this diazotroph to grow with molecular dinitrogen (N2) as the sole nitrogen source. Here, the Mo responses of the wild type and of a mutant lacking ModABC, the high-affinity molybdate transporter, were examined by proteome profiling, Western analysis, epitope tagging, and lacZ reporter fusions. Many Mo-controlled proteins identified in this study have documented or presumed roles in nitrogen fixation, demonstrating the relevance of Mo control in this highly ATP-demanding process. The levels of Mo-nitrogenase, NifHDK, and the Mo storage protein, Mop, increased with increasing Mo concentrations. In contrast, Fe-nitrogenase, AnfHDGK, and ModABC, the Mo transporter, were expressed only under Mo-limiting conditions. IscN was identified as a novel Mo-repressed protein. Mo control of Mop, AnfHDGK, and ModABC corresponded to transcriptional regulation of their genes by the Mo-responsive regulators MopA and MopB. Mo control of NifHDK and IscN appeared to be more complex, involving different posttranscriptional mechanisms. In line with the simultaneous control of IscN and Fe-nitrogenase by Mo, IscN was found to be important for Fe-nitrogenase-dependent diazotrophic growth. The possible role of IscN as an A-type carrier providing Fe-nitrogenase with Fe-S clusters is discussed. IMPORTANCE Biological nitrogen fixation is a central process in the global nitrogen cycle by which the abundant but chemically inert dinitrogen (N2) is reduced to ammonia (NH3), a bioavailable form of nitrogen. Nitrogen reduction is catalyzed by nitrogenases found in diazotrophic bacteria and archaea but not in eukaryotes. All diazotrophs synthesize molybdenum-dependent nitrogenases. In addition, some diazotrophs, including Rhodobacter capsulatus, possess catalytically less efficient alternative Mo-free nitrogenases, whose expression is repressed by Mo. Despite the importance of Mo in biological nitrogen fixation, this is the first study analyzing the proteome-wide Mo response in a diazotroph. IscN was recognized as a novel member of the molybdoproteome in R. capsulatus. It was dispensable for Mo-nitrogenase activity but supported diazotrophic growth under Mo-limiting conditions.
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11
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Reis VM, Teixeira KRDS. Nitrogen fixing bacteria in the family Acetobacteraceae and their role in agriculture. J Basic Microbiol 2015; 55:931-49. [PMID: 25736602 PMCID: PMC7166518 DOI: 10.1002/jobm.201400898] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2014] [Accepted: 01/27/2015] [Indexed: 11/17/2022]
Abstract
For centuries, the Acetobacteraceae is known as a family that harbors many species of organisms of biotechnological importance for industry. Nonetheless, since 1988 representatives of this family have also been described as nitrogen fixing bacteria able to plant growth promotion by a variety of mechanisms. Nitrogen fixation is a biological process that guarantees that the atmospheric N2 is incorporated into organic matter by several bacterial groups. Most representatives of this group, also known as diazotrophic, are generally associated with soil rhizosphere of many plants and also establishing a more specific association living inside roots, leaves, and others plants tissues as endophyte. Their roles as plant growth-promoting microorganisms are generally related to increase in plant biomass, phosphate and other mineral solubilization, and plant pathogen control. Here, we report many of these plant growth-promoting processes related to nitrogen fixing species already described in Acetobacteraceae family, especially Gluconacetobacter diazotrophicus and their importance to agriculture. In addition, a brief review of the state of art of the phylogenetics, main physiological and biochemical characteristics, molecular and functional genomic data of this group of Acetobacteraceae is presented.
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