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J. Bacteriol. doi:10.1128/JB.00082-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Gene expression analysis of long-term lactic acid adapted Corynebacterium glutamicum

Lehrstuhl für Mikrobielle Ökologie, Technische Universität München, D-85354 Freising, Germany, Institut für Molekulare Mikrobiologie und Biotechnologie, Westfälische Wilhelms Universität Münster, D-48149 Münster, Germany

^* To whom correspondence should be addressed. Email: siegfried.scherer{at}wzw.tum.de.

	Abstract

Corynebacteria form an important part of the red smear cheese microbial surface consortia. To gain a better understanding of the molecular adaptation due to low pH induced by lactose fermentation, the global gene expression profile of Corynebacterium glutamicum adapted to pH 5.7 with lactic acid under continuous growth in a chemostat was characterized by DNA microarray analysis. Expression of a total of 116 genes was increased and of 90 genes was decreased as compared to pH 7.5 without lactic acid, representing 7% of the genes in the genome. The up-regulated genes encode mainly for transcriptional regulators, proteins responsible for ex- and import, metabolism and several proteins of unknown fucnction. As much as 45% of the up regulated ORFs code for hypothetical proteins. These results were validated using real time RT-PCR. To characterize the function of 38 up-regulated genes, 36 single crossover disruption mutants were generated and analyzed for their lactic acid sensitivity. However, only a sigB knock-out mutant showed a highly significant negative effect on growth at low pH, suggesting a function in organic acid adaptation. A sigE mutant displayed growth retardation already at neutral pH, but grew better at acidic pH than the sigB mutant. The lack of acid sensitive phenotypes in 34 out of 36 disrupted genes suggests either a considerable redundancy in acid adaptation response or coincidental effects. Other up-regulated genes included ion transporters and genes for metabolic pathways including carbohydrate and respiratory metabolism. The enhanced expression of the nrd (ribonucleotide reductase) operon and a DNA ATPase repair protein implies a cellular response to combat acid induced damage of DNA. Surprisingly, multiple iron uptake systems (totaling 15% of the genes induced 2-fold) were induced at low pH. This induction was shown to be coincidental and could be attributed to iron sequestering effects in complex media at low pH.

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