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Journal of Bacteriology, July 2009, p. 4251-4258, Vol. 191, No. 13
0021-9193/09/$08.00+0     doi:10.1128/JB.00303-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

The ldhA Gene, Encoding Fermentative L-Lactate Dehydrogenase of Corynebacterium glutamicum, Is under the Control of Positive Feedback Regulation Mediated by LldR{triangledown}

Koichi Toyoda, Haruhiko Teramoto, Masayuki Inui, and Hideaki Yukawa*

Research Institute of Innovative Technology for the Earth (RITE), 9-2 Kizugawadai, Kizugawa, Kyoto 619-0292, Japan

Received 5 March 2009/ Accepted 28 April 2009

Corynebacterium glutamicum ldhA encodes L-lactate dehydrogenase, a key enzyme that couples L-lactate production to reoxidation of NADH formed during glycolysis. We previously showed that in the absence of sugar, SugR binds to the ldhA promoter region, thereby repressing ldhA expression. In this study we show that LldR is another protein that binds to the ldhA promoter region, thus regulating ldhA expression. LldR has hitherto been characterized as an L-lactate-responsive transcriptional repressor of L-lactate utilization genes. Transposon mutagenesis of a reporter strain carrying a chromosomal ldhA promoter-lacZ fusion (PldhA-lacZ) revealed that ldhA disruption drastically decreased expression of PldhA-lacZ. PldhA-lacZ expression in the ldhA mutant was restored by deletion of lldR, suggesting that LldR acts as a repressor of ldhA in the absence of L-lactate and the LldR-mediated repression is not relieved in the ldhA mutant due to its inability to produce L-lactate. lldR deletion did not affect PldhA-lacZ expression in the wild-type background during growth on either glucose, acetate, or L-lactate. However, it upregulated PldhA-lacZ expression in the sugR mutant background during growth on acetate. The binding sites of LldR and SugR are located around the –35 and –10 regions of the ldhA promoter, respectively. C. glutamicum ldhA expression is therefore primarily repressed by SugR in the absence of sugar. In the presence of sugar, SugR-mediated repression of ldhA is alleviated, and ldhA expression is additionally enhanced by LldR inactivation in response to L-lactate produced by LdhA.

* Corresponding author. Mailing address: Research institute of Innovative Technology for the Earth (RITE), 9-2 Kizugawadai, Kizugawa, Kyoto 619-0292, Japan. Phone: 81-774-75-2308. Fax: 81-774-75-2321. E-mail: mmg-lab{at}rite.or.jp

{triangledown} Published ahead of print on 1 May 2009.

Journal of Bacteriology, July 2009, p. 4251-4258, Vol. 191, No. 13
0021-9193/09/$08.00+0     doi:10.1128/JB.00303-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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