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Journal of Bacteriology, August 2007, p. 5582-5590, Vol. 189, No. 15
0021-9193/07/$08.00+0     doi:10.1128/JB.00082-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Gene Expression Analysis of Corynebacterium glutamicum Subjected to Long-Term Lactic Acid Adaptation{triangledown} ,¶

Kinga Jakob,1,{dagger} Peter Satorhelyi,1,{dagger},§ Christian Lange,2 Volker F. Wendisch,2 Barbara Silakowski,1,{ddagger} Siegfried Scherer,1* and Klaus Neuhaus1

Lehrstuhl für Mikrobielle Ökologie, Technische Universität München, D-85354 Freising, Germany,1 Institut für Molekulare Mikrobiologie und Biotechnologie, Westfälische Wilhelms Universität Münster, D-48149 Münster, Germany2

Received 16 January 2007/ Accepted 14 May 2007

Corynebacteria form an important part of the red smear cheese microbial surface consortium. To gain a better understanding of 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 that of 90 genes was decreased compared to pH 7.5 without lactic acid, representing 7% of the genes in the genome. The up-regulated genes encode mainly transcriptional regulators, proteins responsible for export, import, and metabolism, and several proteins of unknown function. As much as 45% of the up-regulated open reading frames code for hypothetical proteins. These results were validated using real-time reverse transcription-PCR. To characterize the functions of 38 up-regulated genes, 36 single-crossover disruption mutants were generated and analyzed for their lactic acid sensitivities. However, only a sigB knockout mutant showed a highly significant negative effect on growth at low pH, suggesting a function in organic-acid adaptation. A sigE mutant already displayed growth retardation 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 genes for ion transporters and 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 DNA damage. 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.

* Corresponding author. Mailing address: Lehrstuhl für Mikrobielle Ökologie, Technische Universität München, Weihenstephaner Berg 3, D-85350 Freising, Germany. Phone: 49 8161 713516. Fax: 49 8161 714512. E-mail: siegfried.scherer{at}wzw.tum.de

{triangledown} Published ahead of print on 25 May 2007.

Supplemental material for this article may be found at http://jb.asm.org/.

{dagger} K. Jakob and P. Satorhelyi contributed equally to this work.

§ Present address: IVAX Drug Research Institute, Budapest 1045, Hungary.

{ddagger} Present address: Food Science Division, Bio-Rad Laboratories GmbH, D-80939 München, Germany.

Journal of Bacteriology, August 2007, p. 5582-5590, Vol. 189, No. 15
0021-9193/07/$08.00+0     doi:10.1128/JB.00082-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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