Characterization of a Corynebacterium glutamicum lactate utilization operon induced during temperature-triggered glutamate production

Gene expression changes of glutamate-producing Corynebacterium glutamicum were identified in transcriptome comparisons by DNA microarray analysis. During glutamate production induced by a temperature shift, C glutamicum strain 2262 showed significantly higher mRNA levels of the NCgl2816 and NCgl2817 genes than its non-glutamate- producing derivative 2262NP. Reverse transcription-PCR analysis showed that the two genes together constitute an operon. NCgl2816 putatively codes for a lactate permease, while NCgl2817 was demonstrated to encode quinone-dependent L-lactate dehydrogenase, which was named LldD. C. glutamicum LldD displayed Michaelis-Menten kinetics for the substrate L-lactate with a K(m) of about 0.51 mM. The specific activity of LIdD was about 10-fold higher during growth on L-lactate or on an L-lactate-glucose mixture than during growth on glucose, D-lactate, or pyruvate, while the specific activity of quinone-dependent D-lactate dehydrogenase differed little with the carbon source. RNA levels of NCg12816 and ildD were about 18-fold higher during growth on L-lactate than on pyruvate. Disruption of the NCg12816-ildD operon resulted in loss of the ability to utilize L-lactate as the sole carbon source. Expression of ildD restored L-lactate utilization, indicating that the function of the permease gene NCgl2816 is dispensable, while LIdD is essential, for growth of C. glutamicum on L-lactate.