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Title: Metabolic Model of the Nitrogen-Fixing Obligate Aerobe Azotobacter vinelandii Predicts Its Adaptation to Oxygen Concentration and Metal Availability

Journal Article · · mBio (Online)

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.

Research Organization:
Washington State University, Pullman, WA (United States)
Sponsoring Organization:
US Department of Agriculture (USDA); USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
SC0018143
OSTI ID:
1904399
Journal Information:
mBio (Online), Journal Name: mBio (Online) Journal Issue: 6 Vol. 12; ISSN 2150-7511
Publisher:
American Society for Microbiology (ASM)Copyright Statement
Country of Publication:
United States
Language:
English

References (66)

Measurement of dissolved oxygen in fermentations journal October 1961
Control of dinitrogen fixation in ammonium-assimilating cultures of Azotobacter vinelandii journal September 1987
Whole cell respiration and nitrogenase activities in Azotobacter vinelandii growing in oxygen controlled continuous culture journal January 1983
Dependency of growth yield, maintenance and K s-values on the dissolved oxygen concentration in continuous cultures of Azotobacter vinelandii journal April 1988
Biochemistry, evolution and physiological function of the Rnf complex, a novel ion-motive electron transport complex in prokaryotes journal November 2010
Poly(3-hydroxybutyrate) accumulation by Azotobacter vinelandii under different oxygen transfer strategies journal January 2019
The effect of oxygen on nitrogen fixation by Azotobacter journal January 1960
Two NADH:ubiquinone oxidoreductases of Azotobacter vinelandii and their role in the respiratory protection journal February 1998
Evolution of the specific power consumption and oxygen transfer rate in alginate-producing cultures of Azotobacter vinelandii conducted in shake flasks journal September 2007
When yield gaps are poverty traps: The paradigm of ecological intensification in African smallholder agriculture journal March 2013
Modeling of nitrogen fixation and polymer production in the heterotrophic diazotroph Azotobacter vinelandii DJ journal December 2020
Oxygen supply strongly influences metabolic fluxes, the production of poly(3-hydroxybutyrate) and alginate, and the degree of acetylation of alginate in Azotobacter vinelandii journal July 2013
Model-driven evaluation of the production potential for growth-coupled products of Escherichia coli journal May 2010
Metabolic engineering of a diazotrophic bacterium improves ammonium release and biofertilization of plants and microalgae journal March 2017
The Electron Bifurcating FixABCX Protein Complex from Azotobacter vinelandii : Generation of Low-Potential Reducing Equivalents for Nitrogenase Catalysis journal August 2017
Mechanism of N 2 Reduction Catalyzed by Fe-Nitrogenase Involves Reductive Elimination of H 2 journal January 2018
Kinetic Understanding of N 2 Reduction versus H 2 Evolution at the E 4 (4H) Janus State in the Three Nitrogenases journal September 2018
Changes in the Midpoint Potentials of the Nitrogenase Metal Centers as a Result of Iron Protein−Molybdenum-Iron Protein Complex Formation journal October 1997
Mechanism of Nitrogen Fixation by Nitrogenase: The Next Stage journal January 2014
Respiratory Protection of Nitrogenase Activity in Azotobacter vinelandii—Roles of the Terminal Oxidases journal June 1997
Effect of Oxygen on the Fixation of Nitrogen by Azotobacter journal April 1954
A quantitative analysis of the direct and indirect costs of nitrogen fixation: a model based on Azotobacter vinelandii journal October 2016
Flux sampling is a powerful tool to study metabolism under changing environmental conditions journal September 2019
Fluxomic Analysis Reveals Central Carbon Metabolism Adaptation for Diazotroph Azotobacter vinelandii Ammonium Excretion journal September 2019
Exploring the alternatives of biological nitrogen fixation journal January 2018
Genes required for rapid expression of nitrogenase activity in Azotobacter vinelandii journal April 2005
Molybdenum threshold for ecosystem scale alternative vanadium nitrogenase activity in boreal forests journal November 2019
Regulation of Cytochrome bd Expression in the Obligate Aerobe Azotobacter vinelandii by CydR (Fnr) journal February 2000
The Ferredoxin:NAD + Oxidoreductase (Rnf) from the Acetogen Acetobacterium woodii Requires Na + and Is Reversibly Coupled to the Membrane Potential journal September 2013
A low-potential terminal oxidase associated with the iron-only nitrogenase from the nitrogen-fixing bacterium Azotobacter vinelandii journal June 2019
The maintenance energy of bacteria in growing cultures journal October 1965
The global nitrogen cycle in the twenty-first century journal July 2013
Determination of the oxygen affinities of terminal oxidases in Azotobacter vinelandii using the deoxygenation of oxyleghaemoglobin and oxymyoglobin: cytochrome bd is a low-affinity oxidase journal June 1994
Expression and Content of Terminal Oxidases in Azotobacter Vinelandii Grown with Excess NH4+ are Modulated by O2 Supply journal January 1997
The Entner-Doudoroff pathway empowers Pseudomonas putida  KT2440 with a high tolerance to oxidative stress : Perturbing the upper metabolism of journal January 2013
High‐quality genome‐scale metabolic modelling of Pseudomonas putida highlights its broad metabolic capabilities journal November 2019
The Respiratory System of Azotobacter vinelandii. 1. Properties of Phosphorylating Respiratory Membranes journal May 1971
The bioenergetics of electron transport to nitrogenase journal March 1987
Isolation and characterization of oxygen sensitive mutants ofAzotobacter vinelandii journal January 1991
Mutagenesis of a gene encoding a cytochromeo-like terminal oxidase ofAzotobacter vinelandii: A cytochromeomutant is aero-tolerant during nitrogen fixation journal June 1994
Respiratory protection of nitrogenase in Azotobacter species: is a widely held hypothesis unequivocally supported by experimental evidence? journal October 2000
Aerobic Hydrogen Production via Nitrogenase in Azotobacter vinelandii CA6 journal April 2015
Symbiotic Nitrogen Fixation and the Challenges to Its Extension to Nonlegumes journal April 2016
Azotobacter vinelandii Nitrogenase Activity, Hydrogen Production, and Response to Oxygen Exposure journal August 2018
Transcriptional Analysis of an Ammonium-Excreting Strain of Azotobacter vinelandii Deregulated for Nitrogen Fixation journal August 2017
Effect of Oxygen on Formation and Structure of Azotobacter vinelandii Alginate and Its Role in Protecting Nitrogenase journal September 2000
Genome Sequence of Azotobacter vinelandii, an Obligate Aerobe Specialized To Support Diverse Anaerobic Metabolic Processes journal May 2009
Electron Transfer to Nitrogenase in Different Genomic and Metabolic Backgrounds journal February 2018
Evolution of Molybdenum Nitrogenase during the Transition from Anaerobic to Aerobic Metabolism journal March 2015
Transcriptional Profiling of Nitrogen Fixation in Azotobacter vinelandii journal July 2011
Noncoupled NADH:Ubiquinone Oxidoreductase of Azotobacter vinelandii Is Required for Diazotrophic Growth at High Oxygen Concentrations journal December 2001
Nitrogen Fixation and Hydrogen Metabolism in Cyanobacteria journal November 2010
The DeLey-Doudoroff Pathway of Galactose Metabolism in Azotobacter vinelandii journal January 1994
Expression of an alternative nitrogen fixation system in Azotobacter vinelandii. journal January 1982
Purification of a second alternative nitrogenase from a nifHDK deletion strain of Azotobacter vinelandii. journal January 1988
Cloning and mutagenesis of genes encoding the cytochrome bd terminal oxidase complex in Azotobacter vinelandii: mutants deficient in the cytochrome d complex are unable to fix nitrogen in air. journal October 1990
Hydrogenase does not confer significant benefits to Azotobacter vinelandii growing diazotrophically under conditions of glucose limitation journal October 1995
Characterization of the genes coding for the putative sigma factor AlgU and its regulators MucA, MucB, MucC, and MucD in Azotobacter vinelandii and evaluation of their roles in alginate biosynthesis journal April 1996
Formation of pH and potential gradients by the reconstituted Azotobacter vinelandii cytochrome bd respiratory protection oxidase journal June 1997
Distribution of nitrogen fixation and nitrogenase-like sequences amongst microbial genomes journal January 2012
Oxygen transfer rate during the production of alginate by Azotobacter vinelandii under oxygen-limited and non oxygen-limited conditions journal February 2011
Metabolic flux analysis and the NAD(P)H/NAD(P)+ ratios in chemostat cultures of Azotobacter vinelandii journal January 2018
Key factors affecting ammonium production by an Azotobacter vinelandii strain deregulated for biological nitrogen fixation journal May 2020
Elucidation of trophic interactions in an unusual single-cell nitrogen-fixing symbiosis using metabolic modeling journal May 2021
A quantitative model of nitrogen fixation in the presence of ammonium journal November 2018
Nitrogen Fixing Azotobacter Species as Potential Soil Biological Enhancers for Crop Nutrition and Yield Stability journal February 2021