Regulation of nif gene expression and nitrogen metabolism in Azospirillum

Elmerich, Claudine; Zamaroczy, Miklos de; Arsène, Florence; Pereg, Lily; Paquelin, Annick; Kaminski, Annette

doi:10.1016/s0038-0717(96)00228-3

“…Strains, plasmids, media, cell culture and DNA manipulations Null-mutant strains of A. brasilense used were 7628 (Nif ¹ and defective in swarming properties; glnB ::kan; de Zamaroczy et al, 1996), 7148 (Nif þ and defective in both nitrate use and (methyl)ammonium uptake; ntrC ::Tn5 ; Liang et al, 1993;Milcamps et al, 1996) and 7202 (pleiotropic (Nif ¹ ); rpoN mutant; Elmerich et al, 1997). pAB914 carries the glnB gene of A. brasilense (de Zamaroczy et al, 1993), pAB462 and pAB463 contain the A. brasilense glnA gene under the control of its own or an upstream Km promoter respectively .…”

Section: Methodsmentioning

confidence: 99%

Structural homologues P_II and P_z of Azospirillum brasilense provide intracellular signalling for selective regulation of various nitrogen‐dependent functions

Zamaroczy

¹

1998

Molecular Microbiology

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SummaryP II (glnB ) is a signal transduction protein that in Azospirillum brasilense is specifically required for nitrogen fixation. Little is known about whether and how its homologue P z (glnZ ) participates in the regulation of cellular functions. In this study, we have shown the regulatory action of the two proteins by analysing the relevant single and double null-mutant strains. The transcription of glnZ is monocistronic, and it starts mainly from a 54 -dependent promoter, activated by NtrC. glnZ expression is dependent on the ntr system, even under conditions of nitrogen excess, and is greatly enhanced in the presence of aspartate. P z is uridylylated in response to nitrogen limitation, like P II , although different amounts of the two proteins are synthesized. P II is required for the dephosphorylation of NtrC. Thus, in the absence of P II , the repression of nitrate assimilation is not promoted, which, in turn, leads to a high rate of ammonium excretion. Unexpectedly, P II and P z proteins are not essential for the reversible modification of glutamine synthetase. (Methyl)ammonium transport into the cell is negatively regulated by P z . The growth of a double-mutant strain (glnB ::kan ; glnZ ::⍀ ) is drastically disabled, although wild-type growth is restored by complementation with either glnB or glnZ. We conclude that P II and P z , despite their structural similarity, are involved in different regulatory processes, except for that required for cell growth.

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“…Oxygen inhibits nitrogen fixation by direct action on proteins [2] and represses the level of DNA transcription [3,4]. However, as nitrogen fixation is an energy consuming process some oxygen is required for the production of ATP by oxidative phosphorylation.…”

Section: Introductionmentioning

confidence: 99%

“…NifH, which encodes the structural polypeptides of nitrogenase reductase, is only expressed under nitrogen fixing conditions [6]. The gene product of nifA, which is directly modulated by oxygen [4], activates it. It follows that a measure of the expression of nifH should be an indication of the potential for nitrogen fixation.…”

Section: Introductionmentioning

confidence: 99%

Improved Potential for Nitrogen Fixation inAzospirillum brasilense Sp7-S Associated with WheatnifH Expression as a Function of Oxygen Pressure

Deaker

¹

,

Kennedy

²

2001

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The use of a nifH-lacZ fusion as an indicator of nitrogen fixing conditions is investigated in relation to two strains of Azospirillum brasilense with contrasting patterns of colonization on wheat roots. The degree of expression of nifH-lacZ of Azospirillum brasilense could be manipulated by controlling the oxygen pressure. A strong correlation between nitrogenase activity and nifH expression was found in pure cultures. nifH expression was maximal at 0.5% oxygen in pure cultures of both the wild type Sp7 and spontaneous mutant Sp7-S. Differentiation of the maximal expression was observed when the two strains were in association with para-nodulated wheat, resulting in greater expression by Sp7-S over a broader range of external oxygen concentrations than by Sp7. This result was observed when expressed as activity per mg of plant protein as well as per bacterium. An increase in nifH expression was also noted with para-nodulated (2,4-D treated) wheat inoculated with Sp7-S when compared with untreated wheat. No significant difference was found between treated and untreated wheat inoculated with Sp7. The results indicate that the majority of the Azospirillum brasilense Sp7-S cells occupy a more protected niche when in association with wheat roots, resulting in conditions that support a greater potential for nitrogen fixation as judged by nifH expression.

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“…Benefit from nitrogen fixation in associations between Azospirillum and wheat may only be achieved if the association sufficiently provides conditions suitable for significant levels of expression of nitrogenase [1]. Oxygen inhibits nitrogen fixation by direct action on proteins [2] and represses the level of DNA transcription [3,4]. However, as nitrogen fixation is an energy consuming process some oxygen is required for the production of ATP by oxidative phosphorylation.…”

Section: Introductionmentioning

confidence: 99%

Improved Potential for Nitrogen Fixation in Azospirillum brasilense Sp7-S Associated with Wheat nifH Expression as a Function of Oxygen Pressure

Deaker¹,

Kennedy²

2001

Acta Biotechnol.

1

0

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The use of a nifH-lacZ fusion as an indicator of nitrogen fixing conditions is investigated in relation to two strains of Azospirillum brasilense with contrasting patterns of colonization on wheat roots. The degree of expression of nifH-lacZ of Azospirillum brasilense could be manipulated by controlling the oxygen pressure. A strong correlation between nitrogenase activity and nifH expression was found in pure cultures. nifH expression was maximal at 0.5% oxygen in pure cultures of both the wild type Sp7 and spontaneous mutant Sp7-S. Differentiation of the maximal expression was observed when the two strains were in association with para-nodulated wheat, resulting in greater expression by Sp7-S over a broader range of external oxygen concentrations than by Sp7. This result was observed when expressed as activity per mg of plant protein as well as per bacterium. An increase in nifH expression was also noted with para-nodulated (2,4-D treated) wheat inoculated with Sp7-S when compared with untreated wheat. No significant difference was found between treated and untreated wheat inoculated with Sp7. The results indicate that the majority of the Azospirillum brasilense Sp7-S cells occupy a more protected niche when in association with wheat roots, resulting in conditions that support a greater potential for nitrogen fixation as judged by nifH expression.

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Regulation of nif gene expression and nitrogen metabolism in Azospirillum

Cited by 23 publications

References 35 publications

Structural homologues P_II and P_z of Azospirillum brasilense provide intracellular signalling for selective regulation of various nitrogen‐dependent functions

Structural homologues P_II and P_z of Azospirillum brasilense provide intracellular signalling for selective regulation of various nitrogen‐dependent functions

Improved Potential for Nitrogen Fixation inAzospirillum brasilense Sp7-S Associated with WheatnifH Expression as a Function of Oxygen Pressure

Improved Potential for Nitrogen Fixation in Azospirillum brasilense Sp7-S Associated with Wheat nifH Expression as a Function of Oxygen Pressure

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Regulation of nif gene expression and nitrogen metabolism in Azospirillum

Cited by 23 publications

References 35 publications

Structural homologues PII and Pz of Azospirillum brasilense provide intracellular signalling for selective regulation of various nitrogen‐dependent functions

Structural homologues PII and Pz of Azospirillum brasilense provide intracellular signalling for selective regulation of various nitrogen‐dependent functions

Improved Potential for Nitrogen Fixation inAzospirillum brasilense Sp7-S Associated with WheatnifH Expression as a Function of Oxygen Pressure

Improved Potential for Nitrogen Fixation in Azospirillum brasilense Sp7-S Associated with Wheat nifH Expression as a Function of Oxygen Pressure

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Structural homologues P_II and P_z of Azospirillum brasilense provide intracellular signalling for selective regulation of various nitrogen‐dependent functions

Structural homologues P_II and P_z of Azospirillum brasilense provide intracellular signalling for selective regulation of various nitrogen‐dependent functions