The mechanism of L-glutamate-overproduction by Corynebacterium glutamicum, a biotin auxotroph, is very unique and interesting. L-Glutamate overproduction by this bacterium is induced by biotin-limitation and suppressed by an excess of biotin. Addition of a surfactant or penicillin is also induces L-glutamate overproduction even under excess biotin. After the development of general molecular biological tools such as cloning vectors and DNA transfer techniques, genes encoding biosynthetic enzymes were isolated. With those genes and tools, recombinant DNA technology can be applied to the analysis of biosynthetic pathways and the construction of C. glutamicum strains. In this review, recent studies on the triggering mechanism of L-glutamate overproduction by C. glutamicum are discussed. Disruption of the dtsR1 gene, which encodes a putative component of a biotin-containing enzyme complex that is involved in fatty acid synthesis, causes constitutive overproduction of L-glutamate. As in the case of biotin-limitation, i.e., addition of a surfactant or penicillin, dtsR1-disruption also reduces the activity of the 2-oxoglutarate dehydrogense complex (ODHC). These results indicate that the DtsR1 level affects the activity of ODHC. In our recent studies, a novel regulatory factor that suppresses the expression of DtsR1 was determined. Based on these findings, the triggering mechanism of L-glutamate overproduction is expected to be clarified in more detail.
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