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Applied and Environmental Microbiology, October 2005, p. 5920-5928, Vol. 71, No. 10
0099-2240/05/$08.00+0 doi:10.1128/AEM.71.10.5920-5928.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Institute of Biotechnology 1, Research Center Juelich, D-52428 Juelich, Germany,1 Laboratoire des Sciences du Genie Chimique, Institut National Polytechnique de Lorraine, 54505 Vandoeuvre-les-Nancy, France2
Received 18 March 2005/ Accepted 6 May 2005
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 Km of about 0.51 mM. The specific activity of LldD 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 NCgl2816 and lldD were about 18-fold higher during growth on L-lactate than on pyruvate. Disruption of the NCgl2816-lldD operon resulted in loss of the ability to utilize L-lactate as the sole carbon source. Expression of lldD restored L-lactate utilization, indicating that the function of the permease gene NCgl2816 is dispensable, while LldD is essential, for growth of C. glutamicum on L-lactate.
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