Identification of a Gene Encoding a Transporter Essential for Utilization of C 4 Dicarboxylates in Corynebacterium glutamicum

Abstract

ABSTRACT 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 [ 13 C]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.