Dicarboxylic Acid Utilisation and Regulation of Nitrogen Fixation in Rhizobium species

Summary Different classes of R. meliloti mutants all exhibiting a Dct - phenotype have been generated and used to clone genes involved in the transport of dicarboxylic acids. Plasmid pRK290:4:46, containing a 40 kb R. meliloti DNA insert, can complement some of the Dct - strains and in addition can confer enhanced succinate uptake activity to strains into which it has been transferred. A Bradyrhizobium japonicum strain containing plasmid pRK290:4:46 exhibits both increased succinate uptake and increased nitrogen fixation activities under free-living conditions.