Identification of a gene encoding a transporter essential for utilization of C-4 dicarboxylates in Corynebacterium glutamicum

The Corynebacterium glutamicum R genome contains a total of eight genes encoding proteins with sequence similarity to C-4-dicarboxylate transporters identified from other bacteria. Three of the genes encode proteins within the dicarboxylate/amino acid: cation symporter (DAACS) family, another three encode proteins within the tripartite ATP-independent periplasmic transporter family, and two encode proteins within the divalent anion: Na+ symporter (DASS) family. We observed that a mutant strain deficient in one of these genes, designated dcsT, of the DASS family did not aerobically grow on the C-4 dicarboxylates succinate, fumarate, and malate as the sole carbon sources. Mutant strains deficient in each of the other seven genes grew as well as the wild-type strain under the same conditions, although one of these genes is a homologue of dctA of the DAACS family, involved in aerobic growth on C-4 dicarboxylates in various bacteria. The utilization of C-4 dicarboxylates was markedly enhanced by overexpression of the dcsT gene. We confirmed that the uptake of [C-13] labeled succinate observed for the wild-type cells was hardly detected in the dcsT-deficient mutant but was markedly enhanced in a dcsT-overexpressing strain. These results suggested that in C. glutamicum, the uptake of C-4 dicarboxylates for aerobic growth was mainly mediated by the DASS transporter encoded by dcsT. The expression level of the dcsT gene transiently increased in the early exponential phase during growth on nutrient-rich medium. This expression was enhanced by the addition of succinate in the mid-exponential phase and was repressed by the addition of glucose in the early exponential phase.