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

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 control...

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Veröffentlicht in:Acta biotechnologica 2001-01, Vol.21 (1), p.3-17
Hauptverfasser: Deaker, R., Kennedy, I.R.
Format: Artikel
Sprache:eng
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Zusammenfassung: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.
ISSN:0138-4988
1521-3846
DOI:10.1002/1521-3846(200102)21:1<3::AID-ABIO3>3.0.CO;2-V