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. 1980 Dec;77(12):7342–7346. doi: 10.1073/pnas.77.12.7342

Evidence for an alternative nitrogen fixation system in Azotobacter vinelandii.

P E Bishop, D M Jarlenski, D R Hetherington
PMCID: PMC350499  PMID: 6938981

Abstract

Two Azotobacter vinelandii strains capable of growing on N2(Nif+) were isolated from two different mutant strains that lacked dinitrogenase activity (Nif-). Extracts of N2-grown cells of the two Nif+ strains lacked significant amounts of the "conventional" dinitrogenase protein subunits, as determined by two-dimensional gel electrophoresis. Instead, the extracts contained at least four new proteins that appeared to be ammonia-repressible (i.e., they were not detected in extracts of ammonia-grown cells). Based on the results of genetic backcrosses, the two Nif+ strains were shown to be pseudorevertants. Both Nif+ pseudorevertant strains were able to grow in N-free media lacking molybdenum but containing tungsten (conditions that prevented growth of the wild-type strain). The four new proteins were observed in extracts of N2-fixing cells of the Nif+ pseudorevertants regardless of whether the cells were grown in the presence of molybdenum-starved wild-type A. vinelandii cells grown under N2-fixing conditions. Under conditions of molybdenum deprivation, Nif- mutant strains of several different phenotypic classes underwent phenotypic reversal to Nif+, as shown by their ability to incorporate 15N2 and to grow in N-free media. These results provide evidence that A. vinelandii possesses an alternative N2-fixation system that is expressed during conditions of molybdenum deficiency.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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