Regulation of ldh expression during biotin-limited growth of Corynebacterium glutamicum

1 Université Paris-Sud, IGM, UMR 8621, Orsay F-91405, France 2 Université Paris-Sud, IBBMC, UMR 8619, Orsay F 91405, France 3 CNRS, Orsay F-91405, France Correspondence Armel Guyonvarch armel{at}igmors.u-psud.fr Corynebacterium glutamicum is a biotin-auxotrophic bacterium and some strains efficiently produce glutamic acid under biotin-limiting conditions. In an effort to understand C. glutamicum metabolism under biotin limitation, growth of the type strain ATCC 13032 was investigated in batch cultures and a time-course analysis was performed. A transient excretion of organic acids was observed and we focused our attention on lactate synthesis. Lactate synthesis was due to the ldh -encoded L -lactate dehydrogenase (Ldh). Features of Ldh activity and ldh transcription were analysed. The ldh gene was shown to be regulated at the transcriptional level by SugR, a pleiotropic transcriptional repressor also acting on most phosphotransferase system (PTS) genes. Electrophoretic mobility shift assays (EMSAs) and site-directed mutagenesis allowed the identification of the SugR-binding site. Effector studies using EMSAs and analysis of ldh expression in a ptsF mutant revealed fructose 1-phosphate as a highly efficient negative effector of SugR. Fructose 1,6-bisphosphate also affected SugR binding. Abbreviations: EMSA, electrophoretic mobility shift assay; β -Gal, β -galactosidase; Ldh, lactate dehydrogenase; PTS, phosphotransferase system