Localization of nitrate reductase genes in a 115-kb plasmid ofRhodobacter capsulatusand restoration of NIT+character in nitrate reductase negative mutant or wild-type strains by conjugative transfer of the endogenous plasmid

Abstract

The capacity to reduce nitrate (NIT+ character) of wild-type and mutant strains of the purple nonsulfur bacterium Rhodobacter capsulatus was analysed by the methods of plasmid genetics and by DNA-DNA hybridization techniques. By conjugative introduction of the endogenous 115-kb plasmid of strain AD2 into a plasmid-free NIT− mutant of the same strain the missing assimilatory nitrate reductase activity was restored. By analogous experimental techniques, the capacity to reduce nitrate was also temporarily established in the Rb. capsulatus NIT− wild-type strain B10. DNA-DNA hybridization experiments with the narGHIJ operon of Escherichia coli and napA of Alcaligenes eutrophus yielded positive signals with an 11-kb EcoRI fragment of the AD2 plasmid.