Efforts toward optimization of aerobic biohydrogen reveal details of secondary regulation of biological nitrogen fixation by nitrogenous compounds in Azotobacter vinelandii

Knutson, Carolann M.; Plunkett, Mary H.; Liming, Rachel A.; Barney, Brett M.

doi:10.1007/s00253-018-9363-0

Cited by 13 publications

(9 citation statements)

References 47 publications

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“…Additionally, since this process is not directly coupled to BNF, it could result in a much higher waste of energy than what would be expected for deletion of the hydrogenase, especially as levels of ammonium accumulate outside of the cell. Contrary to what was found when deleting the hydrogenases [29,46], the deletion of amtB did result in an improvement in the rate of ammonium accumulation (Fig. 3), indicating that this process is likely wasting unnecessary energy and limiting ammonium accumulation.…”

Section: Discussioncontrasting

confidence: 62%

“…This optimal temperature for ammonium production contrasts with prior reports. This is not completely unexpected, as the metabolism within this strain has been altered dramatically to achieve this ammonium production phenotype [6,[10][11][12]29].…”

Section: Discussionmentioning

confidence: 82%

“…In this experiment, we sought to determine the highest rate of ammonium accumulation in the extracellular space, regardless of the [27,28]. Based on these calculations, 8-13% of the cellular protein is required as MoFe protein (NifDK) functioning at optimal rates with full activity [27,29]. Achieving these rates in vitro required 10 molar equivalents of Fe protein to MoFe protein [28], while others have reported Fe:MoFe protein ratios of ~ 2:1 within A. vinelandii wild-type cells during maximum in vivo nitrogenase activity [30].…”

Section: Maximizing Rates Of Ammonium Productionmentioning

confidence: 99%

“…Details for strains constructed for use in this study are provided in Table 3. Methods describing the construction of strains AZBB106, and AZBB163 have been described previously [11,29].…”

Section: Genetic Constructs Gene Deletion and Confirmationmentioning

confidence: 99%

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Key factors affecting ammonium production by an Azotobacter vinelandii strain deregulated for biological nitrogen fixation

2020

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Background: The obligate aerobe Azotobacter vinelandii is a model organism for the study of biological nitrogen fixation (BNF). This bacterium regulates the process of BNF through the two component NifL and NifA system, where NifA acts as an activator, while NifL acts as an anti-activator based on various metabolic signals within the cell. Disruption of the nifL component in the nifLA operon in a precise manner results in a deregulated phenotype that produces levels of ammonium that far surpass the requirements within the cell, and results in the release of up to 30 mM of ammonium into the growth medium. While many studies have probed the factors affecting growth of A. vinelandii, the features important to maximizing this high-ammonium-releasing phenotype have not been fully investigated. Results: In this work, we report the effect of temperature, medium composition, and oxygen requirements on sustaining and maximizing elevated levels of ammonium production from a nitrogenase deregulated strain. We further investigated several pathways, including ammonium uptake through the transporter AmtB, which could limit yields through energy loss or futile recycling steps. Following optimization, we compared sugar consumption and ammonium production, to attain correlations and energy requirements to drive this process in vivo. Ammonium yields indicate that between 5 and 8% of cellular protein is fully active nitrogenase MoFe protein (NifDK) under these conditions. Conclusions: These findings provide important process optimization parameters, and illustrate that further improvements to this phenotype can be accomplished by eliminating futile cycles.

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Section: Discussioncontrasting

confidence: 62%

Section: Discussionmentioning

confidence: 82%

Section: Maximizing Rates Of Ammonium Productionmentioning

confidence: 99%

“…Details for strains constructed for use in this study are provided in Table 3. Methods describing the construction of strains AZBB106, and AZBB163 have been described previously [11,29].…”

Section: Genetic Constructs Gene Deletion and Confirmationmentioning

confidence: 99%

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Key factors affecting ammonium production by an Azotobacter vinelandii strain deregulated for biological nitrogen fixation

2020

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“…Heterotrophic diazotrophic representatives found in these environments have included various Proteobacteria, Firmicutes, Spirochetes, and Methanogens ( Riemann et al, 2010 ; Farnelid et al, 2013 ; Bombar et al, 2016 ). Although limited information is currently available, heterotrophic diazotrophs were found to be hindered by high levels of dissolved inorganic nitrogen compounds ( Klugkist and Haaker, 1984 ; Knutson et al, 2018 ), high concentrations of dissolved oxygen ( Goldberg et al, 1987 ; Pedersen et al, 2018 ), as well as low availability of organic carbon ( Rahav et al, 2016 ).…”

Section: Introductionmentioning

confidence: 99%

Contribution of Heterotrophic Diazotrophs to N2 Fixation in a Eutrophic River: Free-Living vs. Aggregate-Associated

2022

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Recent studies have indicated that heterotrophic diazotrophs are highly diverse and fix N2 in aquatic environments with potentially adverse conditions for diazotrophy, such as oxic and rich in total nitrogen. In this study, we compared the activity and diversity of heterotrophic diazotrophs associated with aggregates (>12 μm) to free-living cells in the eutrophic Qishon River during the winter and summer seasons. Overall, measured heterotrophic N2 fixation rates in the Qishon River ranged between 2.6–3.5 nmol N L–1 d–1. Heterotrophic N2 fixation was mainly associated with aggregates in the summer samples (74 ± 24%), whereas during the winter the bulk diazotrophic activity was mostly ascribed to the free-living fraction (90 ± 6%). In addition, immunolabeled micrographs indicated the presence of aggregate-associated heterotrophic diazotrophs in both seasons, while phototrophic diazotrophs were also captured during the winter. The richness of free-living and aggregate-associated heterotrophic diazotrophs were overall similar, yet the evenness of the later was significantly smaller, suggesting that few of the species gained advantage from particle lifestyle. The differences in the activity, micro-localization and diversity of the diazotrophic community were mostly attributed to spatiotemporal changes in the ambient C:N ratios (total organic carbon, TOC: total nitrogen) and the TOC concentrations. Taken together, our results shed new light on the contribution of heterotrophic diazotroph associated with aggregates to total heterotrophic N2 fixation in oxic, highly eutrophic aquatic environments.

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Aerobic nitrogen-fixing bacteria for hydrogen and ammonium production: current state and perspectives

Barney

2019

Appl Microbiol Biotechnol

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Efforts toward optimization of aerobic biohydrogen reveal details of secondary regulation of biological nitrogen fixation by nitrogenous compounds in Azotobacter vinelandii

Cited by 13 publications

References 47 publications

Key factors affecting ammonium production by an Azotobacter vinelandii strain deregulated for biological nitrogen fixation

Key factors affecting ammonium production by an Azotobacter vinelandii strain deregulated for biological nitrogen fixation

Contribution of Heterotrophic Diazotrophs to N2 Fixation in a Eutrophic River: Free-Living vs. Aggregate-Associated

Aerobic nitrogen-fixing bacteria for hydrogen and ammonium production: current state and perspectives

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