Regulation of nitrogen fixation (nif) genes of Azospirillum brasilense by nifA and ntr (gln) type gene products

Abstract Eight Nif⁻ mutants of Azospirillum brasilense were obtained by N -nitrosoguanidine mutagenesis and isolated by growth on glutamate medium. Three of these mutants had no nitrogenase activity, possessed no nitrogenase structural proteins and were complemented by Klebsiella pneumoniae nifA . Evidence will be presented that one of these mutants is defective in a nifA type regulatory gene but the other two were also complemented by K. pneumoniae ntrC and may be ntrC⁻ -type mutants. A fourth mutant was defective in the MoFe component protein of nitrogenase.