Regulatory mutation that controls nif expression and histidine transport in Azospirillum brasilense

Fischer, M.; Levy, Efrat; Geller, Tania

doi:10.1128/jb.167.1.423-426.1986

Cited by 17 publications

(12 citation statements)

References 22 publications

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“…Although an increase of about 2.7-fold was observed in the GDH activity of NH4+-grown A. brasilense as compared with N2-grown A. brasilense (Table 1), with an accompanying increase of 5.8-fold in the ratio of GDH/GOGAT activities, the differences were relatively small. These results are similar to those reported for Clostridium pasteurianum (12) and A. brasilense by others (3,14,17 (Table 1), only a minor fraction of glutamate is formed by GDHcatalyzed direct amination. The 74% inhibition of radiolabeling of glutamine in the presence of DON presumably resulted from depletion of the pool of glutamate as a consequence of inhibition of GOGAT activity (9).…”

Section: Discussionsupporting

confidence: 81%

“…In addition to nitrogenase (3,5,13), the nitrogenmetabolizing enzymes glutamine synthetase (GS; EC 6.3.1.2) (4,5,14), glutamate synthase (GOGAT; EC 1.4.1.13) (2,14,17), and glutamate dehydrogenase (GDH; EC 1.4.1.2) (3,14) have been detected in extracts of A. brasilense. The observations that the activity of GS decreases and that the activity of GDH increases in cells grown with NH4' relative to N2 supported the idea that the route of glutamate formation by A. brasilense varies with the amount of assimilable nitrogen in the environment (14); at low concentrations of available NH4' (growth on N2), the GOGAT cycle (sequential activities of GS and GOGAT) is thought to predominate, while the GDH route is the primary reaction at high NH4+ concentrations.…”

mentioning

confidence: 99%

“…The heterotrophic, microaerobic diazotroph Azospirillum brasilense has been found in abundant numbers in the rhizosphere of specific grasses (1) as well as in the intercellular spaces in the roots of certain cereals (15). These relationships are viewed as associative symbioses (6), in which the bacteria receive nonspecific photosynthate carbon from the plant and, in turn, provide the plant with fixed nitrogen.In addition to nitrogenase (3,5,13), the nitrogenmetabolizing enzymes glutamine synthetase (GS; EC 6.3.1.2) (4, 5, 14), glutamate synthase (GOGAT; EC 1.4.1.13) (2, 14, 17), and glutamate dehydrogenase (GDH; EC 1.4.1.2) (3, 14) have been detected in extracts of A. brasilense. The observations that the activity of GS decreases …”

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confidence: 99%

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confidence: 99%

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Assimilation of 13NH4+ by Azospirillum brasilense grown under nitrogen limitation and excess

Westby¹,

Enderlin²,

Steinberg³

et al. 1987

J Bacteriol

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The specific activities of glutamine synthetase (GS) and glutamate synthase (GOGAT) were 4.2-and 2.2-fold higher, respectively, in cells of Azospirillum brasilense grown with N2 than with 43 mM NH4' as the source of nitrogen. Conversely, the specific activity of glutamate dehydrogenase (GDH) was 2.7-fold higher in 43 mM NH4+-grown cells than in N2-grown cells. These results indicate that NH4' could be assimilated and that glutamate could be formed by either the GS-GOGAT or GDH pathway or both, depending on the cellular concentration of NH4'. The routes of in vivo synthesis of glutamate were identified by using 13N as a metabolic tracer. The products of assimilation of 13N114' were, in order of decreasing radioactivity, glutamine, glutamate, and alanine. The heterotrophic, microaerobic diazotroph Azospirillum brasilense has been found in abundant numbers in the rhizosphere of specific grasses (1) as well as in the intercellular spaces in the roots of certain cereals (15). These relationships are viewed as associative symbioses (6), in which the bacteria receive nonspecific photosynthate carbon from the plant and, in turn, provide the plant with fixed nitrogen.In addition to nitrogenase (3,5,13), the nitrogenmetabolizing enzymes glutamine synthetase (GS; EC 6.3.1.2) (4, 5, 14), glutamate synthase (GOGAT; EC 1.4.1.13) (2, 14, 17), and glutamate dehydrogenase (GDH; EC 1.4.1.2) (3, 14) have been detected in extracts of A. brasilense. The observations that the activity of GS decreases

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Section: Discussionsupporting

confidence: 81%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Assimilation of 13NH4+ by Azospirillum brasilense grown under nitrogen limitation and excess

Westby¹,

Enderlin²,

Steinberg³

et al. 1987

J Bacteriol

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“…Several regulatory A. brasilense mutants, which showed high nitrogenase activity in the presence of NH4+ 'Iwere isolated. Some of these mutants lacked GS activity (11), and some had effects on histidine transport (9) or NH4' uptake and excretion (22). Unfortunately, neither the nature of these mutations nor their effects on the DRAT/DRAG system were determined.…”

Section: Discussionmentioning

confidence: 99%

Posttranslational regulation of nitrogenase activity in Azospirillum brasilense ntrBC mutants: ammonium and anaerobic switch-off occurs through independent signal transduction pathways

et al. 1994

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Nitrogenase activity is regulated by reversible ADP-ribosylation in response to NH4' and anaerobic conditions in Azospirillum brasilense. The effect of mutations in ntrBC on this regulation was examined. While NH4' addition to ntrBC mutants caused a partial loss of nitrogenase activity, the effect was substantially smaller than that seen in ntr' strains. In contrast, nitrogenase activity in these mutants was normally regulated in response to anaerobic conditions. The analysis of mutants lacking both the ntrBC gene products and dinitrogenase reductase activating glycohydrolase (DRAG) suggested that the primary effect of the ntrBC mutations was to alter the regulation of DRAG activity. Although nif expression in the ntr mutants appeared normal, as judged by activity, glutamine synthetase activity was significantly lower in ntrBC mutants than in the wild type. We hypothesize that this lower glutamine synthetase activity may delay the transduction of the NH4 signal necessary for the inactivation of DRAG, resulting in a reduced response of nitrogenase activity to NH4'. Finally, data presented here suggest that different environmental stimuli use independent signal pathways to affect this reversible ADP-ribosylation system. Biological nitrogen fixation, the reduction of molecular dinitrogen to ammonium, is catalyzed by the nitrogenase complex. This complex consists of two enzymes: dinitrogenase (MoFe protein), which contains the active site of dinitrogen reduction, and dinitrogenase reductase (Fe protein), which donates electrons to dinitrogenase (3). Because nitrogen fixation is a very energy-demanding process, it is not surprising that the nitrogenase system is elaborately regulated at both the transcriptional and posttranslational levels.Transcriptional regulation of nif gene expression appears to be exceedingly complicated, with both global and nif-specific regulators (29). In some diazotrophs, such as Kiebsiella pneumoniae and Rhodobacter capsulatus, the global regulation in response to fixed nitrogen is due to the ntr system, in which the products of ntrB and ntrC (NTRB and NTRC, respectively) are typically required for nif transcription (7,16,36). In some other nitrogen-fixing bacteria, such as Azotobacter vinelandii and Azospirillum brasilense, this does not appear to be true, because mutations in ntrB or ntrC have no obvious effect on nif gene expression (19,34). Posttranslational regulation of nitrogenase activity, which also has been termed switch-off (39), has been found in several diverse nitrogen-fixing bacteria (21). This regulation has been described best for the photosynthetic bacterium Rhodospirillum rubrum and involves reversible mono-ADP-ribosylation of dinitrogenase reductase. Two enzymes that perform this regulation have been found. Dinitrogenase reductase ADPribosyl transferase (DRAT, the gene product of draT) catalyzes the transfer of ADP-ribose from NAD to the Arg-101 residue of one subunit of the dinitrogenase reductase dimer of R rubrum and thus inactivates the enzyme. Dinitrogenase reductas...

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Genetic Characterization of Nif Constitutive Mutants of Azospirullum brasilense

Vitorino

Steffens

Souza

et al. 2002

Nitrogen Fixation: From Molecules to Crop Productivity

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Regulatory mutation that controls nif expression and histidine transport in Azospirillum brasilense

Cited by 17 publications

References 22 publications

Assimilation of 13NH4+ by Azospirillum brasilense grown under nitrogen limitation and excess

Assimilation of 13NH4+ by Azospirillum brasilense grown under nitrogen limitation and excess

Posttranslational regulation of nitrogenase activity in Azospirillum brasilense ntrBC mutants: ammonium and anaerobic switch-off occurs through independent signal transduction pathways

Genetic Characterization of Nif Constitutive Mutants of Azospirullum brasilense

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