THE ROLE OF REGULATORY GENES NIFA, VNFA, ANFA, NFRX, NTRC, AND RPON IN EXPRESSION OF GENES ENCODING THE 3 NITROGENASES OF AZOTOBACTER-VINELANDII

Several regulatory gene mutants of Azotobacter vinelandii were tested for ability to synthesize functional nitrogenase-1 (Nif phenotype), ni trogenase-2 (Vnf), or nitrogenase-3 (Anf). While nifA mutants were Nif (-), Vnf(+), and Anf(+/-), and ntrC mutants were Nif(+), Vnf(+), and A nf(+), nifA ntrC double mutants were Nif(-), Vnf(-), and Anf(-). A vnf A mutant was Nif(+), Vnf(+\-), and Anf(+\-), and an anfA strain was Ni f(+), Vnf(+), and Anf(-). lacZ fusions in the nifH, vnfH, vnfD, anfH, and nifM genes of Azotobacter vinelandii were constructed and introduc ed into wild-type and regulatory mutants of A. vinelandii. Expression of these operons correlated with the growth phenotype of the regulator y mutants. Apparently either NifA or NtrC can activate expression of n ifM. Also, expression of the anf operon required the NifA transcriptio nal activator, although there are no NifA binding sites at appropriate locations upstream of anfH (or anfA). The results confirm previous re ports that VnfA and AnfA are required for expression of vnf and anf ge nes, respectively, and that VnfA is involved in repression of the nifH DK operon in the absence of molybdenum and of the anfHDGK operon in th e presence of vanadium.