The soil bacterium Bacillus subtilis frequently encounters a reduction in temperature in its natural habitats. Here, a combined transcriptomic and proteomic approach has been used to analyse the adaptational responses of B. subtilis to low temperature. Propagation of B. subtilis in minimal medium at 15 degrees C triggered the induction of 279 genes and the repression of 301 genes in comparison to cells grown at 37 degrees C. The analysis thus revealed profound adjustments in the overall gene expression profile in chill-adapted cells. Important transcriptional changes in low-temperature-grown cells comprise the induction of the SigB-controlled general stress regulon, the induction of parts of the early sporulation regulons (SigF, SigE and SigG) and the induction of a regulatory circuit (RapA/PhrA and Opp) that is involved in the fine-tuning of the phosphorylation status of the Spo0A response regulator. The analysis of chill-stress-repressed genes revealed reductions in major catabolic (glycolysis, oxidative phosphorylation, ATP synthesis) and anabolic routes (biosynthesis of purines, pyrimidines, haem and fatty acids) that likely reflect the slower growth rates at low temperature. Low-temperature repression of part of the SigW regulon and of many genes with predicted functions in chemotaxis and motility was also noted. The proteome analysis of chill-adapted cells indicates a major contribution of post-transcriptional regulation phenomena in adaptation to low temperature. Comparative analysis of the previously reported transcriptional responses of cold-shocked B. subtilis cells with this data revealed that cold shock and growth in the cold constitute physiologically distinct phases of the adaptation of B. subtilis to low temperature.