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Descripción
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| In the presence of nitrate, Azotobacter vinelandii is able to assimilate nitrogen by using nitrogenase and nitrate reductase/nitrite reductase pathways simultaneously. Nitrogenase and nitrate reductase are Mo-enzymes containing FeMo-co and Mo-MGD at their active sites, respectively. In order to optimize the use of Mo, a scarce metal in nature, regulation of Mo distribution between both enzymes must be strictly controlled during nitrogen assimilation processes. The nifO and nifQ genes are grouped together with nifB, fdxN and rhdN in one transcriptional unit. Despite the similar transcription profile of genes within the nifB operon (1), NifO and NifQ protein levels in Mo-free media differ. While NifO reaches higher levels in Mo-free medium than in Mo-containing medium, NifQ levels are lower (2). The nifO mutant showed a Nif- phenotype in the presence of nitrate, whereas its overexpression lowered nitrate reductase activity (3). NifQ has been characterized as the physiological Mo donor to NifEN in FeMo-co synthesis (4). No role has yet been assigned to NifO. We aimed to understand the relationship between NifO and NifQ in the distribution of Mo between nitrate reductase and nitrogenase. The accumulation of nitrogenase and nitrate reductase structural components and enzymatic activities were analyzed in ?nifO and ?nifQ mutants as well as in nifO and nifQ overexpressing strains of A. vinelandii. The effect of these mutations in nif, nas and mod gene expression was also studied. Finally, the characterization of NifQ purified from cells with different genetic backgrounds that were grown under different conditions of nitrogen and metal availability has been carried out. Analysis of nitrogenase and nitrate reductase activities revealed that, similarly to the nifO mutant (2,3), the nifQ overexpressing strain exhibited lower nitrogenase activity and higher nitrate reductase activity than wild-type when grown diazotrophically in the presence of nitrate. Antagonistic effects between nifO and nifQ are observed in the mutant and in the overexpressing strains. | |
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Internacional
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Si |
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Nombre congreso
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ENFC2014- 11th European Nitrogen Fixation Conference |
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Tipo de participación
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970 |
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Lugar del congreso
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Tenerife |
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Revisores
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Si |
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ISBN o ISSN
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0000-0000 |
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DOI
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Fecha inicio congreso
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07/09/2014 |
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Fecha fin congreso
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10/09/2014 |
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Desde la página
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144 |
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Hasta la página
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144 |
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Título de las actas
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Nitrogenase and nitrate reductase activities of Azotobacter vinelandii nifO and nifQ mutants growing diazotrophically in the presence of nitrate |