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

mBio ◽  
2021 ◽  
Author(s):  
Alexander B. Alleman ◽  
Florence Mus ◽  
John W. Peters
Keyword(s):  
Oxygen Concentration ◽  
Crop Yields ◽  
Azotobacter Vinelandii ◽  
Metabolic Model ◽  
Metal Availability ◽  
Nitrogen Fixing ◽  
Obligate Aerobe

The world’s dependence on industrially produced nitrogenous fertilizers has created a dichotomy of issues. First, parts of the globe lack access to fertilizers, leading to poor crop yields that significantly limit nutrition while contributing to disease and starvation.

scholarly journals Metabolic model of nitrogen-fixing obligate aerobe Azotobacter vinelandii demonstrates adaptation to oxygen concentration and metal availability

2021 ◽  
Author(s):  
Alexander B Alleman ◽  
Florence Mus ◽  
John W Peters
Keyword(s):  
Nitrogen Fixation ◽  
Biological Nitrogen Fixation ◽  
Azotobacter Vinelandii ◽  
Metabolic Model ◽  
Metal Availability ◽  
Respiratory Protection ◽  
Nitrogen Fixing ◽  
A Genome ◽  
Biological Nitrogen ◽  
Genome Scale

There is considerable interest in promoting biological nitrogen fixation as a mechanism to reduce the inputs of nitrogenous fertilizers in agriculture, a problem of agronomic, economic, and environmental importance. For the potential impact of biological nitrogen fixation in agriculture to be realized, there are considerable fundamental knowledge gaps that need to be addressed. Biological nitrogen fixation or the reduction of N2 to NH3 is catalyzed by nitrogenase which requires a large amount of energy in the form of ATP and low potential electrons. Nitrogen-fixing organisms that respire aerobically have an advantage in meeting the energy demands of biological nitrogen fixation but face challenges of protecting nitrogenase from inactivation in the presence of oxygen. Here, we have constructed a genome-scale metabolic model of the aerobic metabolism of nitrogen-fixing bacteria Azotobacter vinelandii, which uses a complex electron transport system, termed respiratory protection, to consume oxygen at a high rate keeping intracellular conditions microaerobic. Our model accurately determines growth rate under high oxygen and high substrate concentration conditions, demonstrating the large flux of energy directed to respiratory protection. While respiratory protection mechanisms compensate the energy balance in high oxygen conditions, it does not account for all substrate intake, leading to increased maintenance rates. We have also shown how A. vinelandii can adapt under different oxygen concentrations and metal availability by rearranging flux through the electron transport system. Accurately determining the energy balance in a genome-scale metabolic model is required for future engineering approaches.

Gene Fitness of Azotobacter vinelandii Under Diazotrophic Growth

2021 ◽  
Author(s):  
Carolann M. Knutson ◽  
Meghan N. Pieper ◽  
Brett M. Barney
Keyword(s):  
Nitrogen Fixation ◽  
Azotobacter Vinelandii ◽  
Genetic Manipulation ◽  
Nitrogen Fixing ◽  
Obligate Aerobe ◽  
Dependent Growth ◽  
Metal Cofactors ◽  
Biological Nitrogen ◽  
Diazotrophic Growth ◽  
Reference Tool

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 3800 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.

scholarly journals A Genome-Scale Metabolic Model of Anabaena 33047 to Guide Genetic Modifications to Overproduce Nylon Monomers

Metabolites ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 168
Author(s):  
John I. Hendry ◽  
Hoang V. Dinh ◽  
Debolina Sarkar ◽  
Lin Wang ◽  
Anindita Bandyopadhyay ◽  
...  
Keyword(s):  
Electron Transport ◽  
Pyruvate Decarboxylase ◽  
Metabolic Model ◽  
Cell Types ◽  
Economic Feasibility ◽  
Nitrogen Fixing ◽  
Design Algorithm ◽  
A Genome ◽  
Anabaena Sp ◽  
Genome Scale

Nitrogen fixing-cyanobacteria can significantly improve the economic feasibility of cyanobacterial production processes by eliminating the requirement for reduced nitrogen. Anabaena sp. ATCC 33047 is a marine, heterocyst forming, nitrogen fixing cyanobacteria with a very short doubling time of 3.8 h. We developed a comprehensive genome-scale metabolic (GSM) model, iAnC892, for this organism using annotations and content obtained from multiple databases. iAnC892 describes both the vegetative and heterocyst cell types found in the filaments of Anabaena sp. ATCC 33047. iAnC892 includes 953 unique reactions and accounts for the annotation of 892 genes. Comparison of iAnC892 reaction content with the GSM of Anabaena sp. PCC 7120 revealed that there are 109 reactions including uptake hydrogenase, pyruvate decarboxylase, and pyruvate-formate lyase unique to iAnC892. iAnC892 enabled the analysis of energy production pathways in the heterocyst by allowing the cell specific deactivation of light dependent electron transport chain and glucose-6-phosphate metabolizing pathways. The analysis revealed the importance of light dependent electron transport in generating ATP and NADPH at the required ratio for optimal N2 fixation. When used alongside the strain design algorithm, OptForce, iAnC892 recapitulated several of the experimentally successful genetic intervention strategies that over produced valerolactam and caprolactam precursors.

Optimal conditions for induction of competence in nitrogen-fixing Azotobacter vinelandii

1982 ◽  
Vol 28 (4) ◽  
pp. 389-397 ◽  
Author(s):  
William J. Page
Keyword(s):  
Dissolved Oxygen ◽  
Sodium Acetate ◽  
Azotobacter Vinelandii ◽  
Nitrogenase Activity ◽  
Cell Mass ◽  
Apparent Competition ◽  
Competence Development ◽  
Optimal Conditions ◽  
Nitrogen Fixing ◽  
Ph Range

Competence development in nitrogen-fixing Azotobacter vinelandii cells was optimal at pH 7.2–7.4 which necessitated additional buffering of the iron-limited nitrogen-free competence medium or the addition of a suitable organic acid salt, e.g., sodium acetate. An autolysin was active in this pH range and competent cells were more susceptible to autolysis than the general cell population. Competence development also required restricted aeration of the culture, and only those cultures that attained zero dissolved oxygen became competent. Restricted aeration served to protect the iron-limited cell nitrogenase from oxygen inactivation thus allowing the culture to reach zero dissolved oxygen. The inclusion of additional sources of reductant, e.g., malate, in buffered competence medium resulted in increased respiration and protection of nitrogenase, increased cell mass, and poly-β-hydroxybutyrate synthesis, but decreased competence. A possible explanation for the apparent competition between competence development and nitrogenase activity is discussed.

scholarly journals Gene Deletions Resulting in Increased Nitrogen Release by Azotobacter vinelandii: Application of a Novel Nitrogen Biosensor

2015 ◽  
Vol 81 (13) ◽  
pp. 4316-4328 ◽  
Author(s):  
Brett M. Barney ◽  
Lauren J. Eberhart ◽  
Janet M. Ohlert ◽  
Carolann M. Knutson ◽  
Mary H. Plunkett
Keyword(s):  
Insertional Mutagenesis ◽  
Azotobacter Vinelandii ◽  
Regulatory System ◽  
Ammonium Transporter ◽  
Gene Deletions ◽  
Content Type ◽  
Living Bacterium ◽  
Obligate Aerobe ◽  
Biosensor Strain ◽  
Alternative Approaches

ABSTRACTAzotobacter vinelandiiis a widely studied model diazotrophic (nitrogen-fixing) bacterium and also an obligate aerobe, differentiating it from many other diazotrophs that require environments low in oxygen for the function of the nitrogenase. As a free-living bacterium,A. vinelandiihas evolved enzymes and transporters to minimize the loss of fixed nitrogen to the surrounding environment. In this study, we pursued efforts to target specific enzymes and further developed screens to identify individual colonies ofA. vinelandiiproducing elevated levels of extracellular nitrogen. Targeted deletions were done to convert urea into a terminal product by disrupting the urease genes that influence the ability ofA. vinelandiito recycle the urea nitrogen within the cell. Construction of a nitrogen biosensor strain was done to rapidly screen several thousand colonies disrupted by transposon insertional mutagenesis to identify strains with increased extracellular nitrogen production. Several disruptions were identified in the ammonium transporter geneamtBthat resulted in the production of sufficient levels of extracellular nitrogen to support the growth of the biosensor strain. Further studies substituting the biosensor strain with the green algaChlorella sorokinianaconfirmed that levels of nitrogen produced were sufficient to support the growth of this organism when the medium was supplemented with sufficient sucrose to support the growth of theA. vinelandiiin coculture. The nature and quantities of nitrogen released by urease andamtBdisruptions were further compared to strains reported in previous efforts that altered thenifLAregulatory system to produce elevated levels of ammonium. These results reveal alternative approaches that can be used in various combinations to yield new strains that might have further application in biofertilizer schemes.

Effect of nitrogen source on carbon metabolism by Azotobacter vinelandii OP grown in chemostat and batch culture

1975 ◽  
Vol 21 (6) ◽  
pp. 738-741 ◽  
Author(s):  
W. G. W. Kurz ◽  
T. A. LaRue
Keyword(s):  
Nitrogen Source ◽  
Batch Culture ◽  
Carbon Metabolism ◽  
Azotobacter Vinelandii ◽  
Nitrogen Fixing ◽  
Malic Dehydrogenase ◽  
Specific Activities

Azotobacter vinelandii growing under nitrogen-fixing conditions has higher specific activities of isocitric and malic dehydrogenase than do cells growing on nitrate or ammonia. Results show that the source of nitrogen has an effect on carbon metabolism.

Sign in / Sign up

Export Citation Format

Share Document