Corynebacterium glutamicum is a Gram-positive, rod-shaped, aerobic bacterium used for the fermentative production of
L-glutamate. LldR (NCgl2814) is known as a repressor for
ldhA and
lldD encoding lactate dehydrogenases. LdhA is responsible for production of
L-lactate, while LldD is for its assimilation. Since
L-lactate production was observed as a by-product of glutamate production under biotin-limited conditions, LldR might play a regulatory role in the glutamate metabolism. Here for the first time, we investigated effects of overproduction or deletion of LldR on the glutamate metabolism under biotin-limited conditions in
C. glutamicum. It was found that glutamate production under biotin-limited conditions was decreased by overproduction of LldR. In the wild-type cells,
L-lactate was produced in the first 24 h and it was re-consumed thereafter. On the other hand, in the overproduced cells,
L-lactate was produced like the wild type, but it was not re-consumed. This means that
L-lactate assimilation, which is catalyzed by LldD, was suppressed by the overproduction of LldR, but
L-lactate production, which is catalyzed by LdhA, was not affected, indicating that LldR mainly controls the expression of
lldD but not of
ldhA under biotin-limited conditions. This was confirmed by quantitative real-time RT-PCR. From these results, it is suggested that
L-lactate metabolism, which is controlled by LldR, has a buffering function of the pyruvate pool for glutamate production.
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