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Noncoupled NADH:ubiquinone oxidoreductase of Azotobacter vinelandii is required for diazotrophic growth at high oxygen concentrations.

ABSTRACT: The gene encoding the noncoupled NADH:ubiquinone oxidoreductase (NDH II) from Azotobacter vinelandii was cloned, sequenced, and used to construct an NDH II-deficient mutant strain. Compared to the wild type, this strain showed a marked decrease in respiratory activity. It was unable to grow diazotrophically at high aeration, while it was fully capable of growth at low aeration or in the presence of NH(4)(+). This result suggests that the role of NDH II is as a vital component of the respiratory protection mechanism of the nitrogenase complex in A. vinelandii. It was also found that the oxidation of NADPH in the A. vinelandii respiratory chain is catalyzed solely by NDH II.

SUBMITTER: Bertsova YV

PROVIDER: S-EPMC95528 | biostudies-literature | 2001 Dec

REPOSITORIES: biostudies-literature

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Noncoupled NADH:ubiquinone oxidoreductase of Azotobacter vinelandii is required for diazotrophic growth at high oxygen concentrations.

Bertsova Y V YV Bogachev A V AV Skulachev V P VP

Journal of bacteriology 20011201 23

The gene encoding the noncoupled NADH:ubiquinone oxidoreductase (NDH II) from Azotobacter vinelandii was cloned, sequenced, and used to construct an NDH II-deficient mutant strain. Compared to the wild type, this strain showed a marked decrease in respiratory activity. It was unable to grow diazotrophically at high aeration, while it was fully capable of growth at low aeration or in the presence of NH(4)(+). This result suggests that the role of NDH II is as a vital component of the respiratory ...[more]

PMID: 11698376

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Project description:Overcoming the inhibitory effects of excess environmental ammonium on nitrogenase synthesis or activity and preventing ammonium assimilation have been considered strategies to increase the amount of fixed nitrogen transferred from bacterial to plant partners in associative or symbiotic plant-diazotroph relationships. The GlnE adenylyltransferase/adenylyl-removing enzyme catalyzes reversible adenylylation of glutamine synthetase (GS), thereby affecting the posttranslational regulation of ammonium assimilation that is critical for the appropriate coordination of carbon and nitrogen assimilation. Since GS is key to the sole ammonium assimilation pathway of Azotobacter vinelandii, attempts to obtain deletion mutants in the gene encoding GS (glnA) have been unsuccessful. We have generated a glnE deletion strain, thus preventing posttranslational regulation of GS. The resultant strain containing constitutively active GS is unable to grow well on ammonium-containing medium, as previously observed in other organisms, and can be cultured only at low ammonium concentrations. This phenotype is caused by the lack of downregulation of GS activity, resulting in high intracellular glutamine levels and severe perturbation of the ratio of glutamine to 2-oxoglutarate under excess-nitrogen conditions. Interestingly, the mutant can grow diazotrophically at rates comparable to those of the wild type. This observation suggests that the control of nitrogen fixation-specific gene expression at the transcriptional level in response to 2-oxoglutarate via NifA is sufficiently tight to alone regulate ammonium production at levels appropriate for optimal carbon and nitrogen balance.IMPORTANCE In this study, the characterization of the glnE knockout mutant of the model diazotroph Azotobacter vinelandii provides significant insights into the integration of the regulatory mechanisms of ammonium production and ammonium assimilation during nitrogen fixation. The work reveals the profound fidelity of nitrogen fixation regulation in providing ammonium sufficient for maximal growth but constraining energetically costly excess production. A detailed fundamental understanding of the interplay between the regulation of ammonium production and assimilation is of paramount importance in exploiting existing and potentially engineering new plant-diazotroph relationships for improved agriculture.

Dataset Information

Noncoupled NADH:ubiquinone oxidoreductase of Azotobacter vinelandii is required for diazotrophic growth at high oxygen concentrations.

Publications

Noncoupled NADH:ubiquinone oxidoreductase of Azotobacter vinelandii is required for diazotrophic growth at high oxygen concentrations.

Similar Datasets

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