Alcaligenes hydrogenophilus lithoautotrophy mutants defective in hydrogenase(s) encoded on plasmid and σ54-like factor encoded on chromosome

Abstract

Abstract In the H2-oxidizing bacterium Alcaligenes hydrogenophilus, four kinds of lithoautotrophy mutants were isolated by transposon mutagenesis. Three mutants, which had mutations on the plasmid pHG21-a, lost the activity(ies) of membrane-bound hydrogenase and/or soluble hydrogenase. The mutant defective in both hydrogenase activities had a mutation on the regulator gene for gene expression of both hydrogenases, and the normal regulator gene which coexisted in trans could complement the mutation. This showed that expression of both hydrogenase genes was controlled positively by the product of the regulator gene. The chromosomal mutant exhibited the pleiotropic phenotype, which could not express the hydrogenase genes on pHG21-a and could not assimilate C4-dicarboxylates as carbon sources and nitrate as a nitrogen source for growth. The chromosomal mutant seems to have a mutation on the σ54-like gene.