title: Gene expression analysis of Corynebacterium glutamicum subjected to long-term lactic acid adaptation.
abstract: 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 >or=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.
authors.affiliation: Lehrstuhl für Mikrobielle Okologie, Technische Universität München, D-85354 Freising, Germany.
authors.forename: Kinga
authors.initials: K
authors.lastname: Jakob
authors.forename: Peter
authors.initials: P
authors.lastname: Satorhelyi
authors.forename: Christian
authors.initials: C
authors.lastname: Lange
authors.forename: Volker F
authors.initials: VF
authors.lastname: Wendisch
authors.forename: Barbara
authors.initials: B
authors.lastname: Silakowski
authors.forename: Siegfried
authors.initials: S
authors.lastname: Scherer
authors.forename: Klaus
authors.initials: K
authors.lastname: Neuhaus
mesh_terms: D000222:Adaptation, Physiological; D048230:Corynebacterium glutamicum / Q000235:genetics / Q000502:physiology*; D017353:Gene Deletion; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000378:metabolism*; D016254:Mutagenesis, Insertional; D020411:Oligonucleotide Array Sequence Analysis; D012329:RNA, Bacterial / Q000032:analysis / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D012329:RNA, Bacterial; D012333:RNA, Messenger; D019344:Lactic Acid