Genetic Mapping of the Rhodopseudomonas capsulata Chromosome Shows Non-clustering of Genes Involved in Nitrogen Fixation

Abstract

Summary: The mutant R plasmid pTH10 was used to construct a circular linkage map of the Rhodopseudomonas capsulata B10 chromosome. Mutations affecting nitrogen fixation (nif mutations) were dispersed in several groups on the chromosome. Biochemical analysis of nif mutants allowed identification of the structural gene for the nitrogenase component II or Fe protein (nifH) and a putative regulatory gene, possibly nif A. These two genes appeared closely linked in conjugation experiments, but represented two distinct linkage groups in crosses mediated by gene transfer agent. Other mutants were affected in the synthesis and/or stability of the nitrogenase component I or MoFe protein; synthesis of component II was also affected, but to a lesser extent. In two of these mutants, nitrogenase activity and the content of component I was increased five to sixfold by the addition of 1 mm-molybdate to the growth medium.