Responsible for the transport of dicarboxylates such as succinate, fumarate, and malate from the periplasm across the inner membrane. This transport system plays an essential role in the energy supply of tropical rhizobium-legume symbionts. By succinate, fumarate, and malate. Expression depends on the RpoN sigma factor. Belongs to the dicarboxylate/amino acid:cation symporter (DAACS) (TC 2.A.23) family. There are two genes for DctA in NGR234; one on the sym plasmid, the other on the chromosome.