Supkulsutra Tanyanut, Maeda Tomoya, Kumagai Kosuke, Wachi Masaaki
Department of Bioengineering, Tokyo Institute of Technology, Japan.
J Gen Appl Microbiol. 2013;59(3):207-14. doi: 10.2323/jgam.59.207.
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.
谷氨酸棒杆菌是一种革兰氏阳性、杆状的需氧细菌，用于发酵生产L-谷氨酸。LldR（NCgl2814）是已知的编码乳酸脱氢酶的ldhA和lldD的阻遏物。LdhA负责L-乳酸的产生，而LldD负责其同化作用。由于在生物素限制条件下观察到L-乳酸的产生是谷氨酸生产的副产物，LldR可能在谷氨酸代谢中发挥调节作用。在此，我们首次研究了在生物素限制条件下，LldR的过量表达或缺失对谷氨酸棒杆菌谷氨酸代谢的影响。结果发现，在生物素限制条件下，LldR的过量表达会降低谷氨酸的产量。在野生型细胞中，L-乳酸在最初24小时内产生，此后被重新消耗。另一方面，在过量表达LldR的细胞中，L-乳酸的产生与野生型相似，但没有被重新消耗。这意味着由LldD催化的L-乳酸同化作用被LldR的过量表达所抑制，但由LdhA催化的L-乳酸产生不受影响，表明在生物素限制条件下，LldR主要控制lldD的表达而不是ldhA的表达。这通过定量实时RT-PCR得到了证实。从这些结果可以看出，由LldR控制的L-乳酸代谢对谷氨酸生产的丙酮酸池具有缓冲作用。
