ABSTRACTThe alternative sigma factor σBof the food pathogenBacillus cereusis activated upon stress exposure and plays a role in the adaptive response of vegetative cells. This study describes the identification of σB-dependent genes inB. cereus. Two-dimensional gel electrophoresis was performed with protein extracts from a σB-overproducingB. cereusstrain. Nine protein spots, which were absent from the negative control, were identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry or N-terminal sequencing. The σB-dependent expression of the corresponding genes was confirmed by Northern blot analysis with RNA isolated fromB. cereusATCC 14579 and itssigBnull mutant. Northern blot analysis also revealed that six other genes were part of σB-dependent operons. The proteins that are predicted to be encoded by the σB-dependent genes include an intracellular protease, a Mg2+transporter, and a thiamine biosynthesis protein (ThiG). Highly conserved promoter sites were found to precede all σB-dependent genes, with the exception ofthiG. By searching theB. cereusgenome for this conserved promoter sequence, five more candidate σB-dependent genes were identified. Northern blot analysis and in vitro transcription experiments with a reconstitutedB. cereusσB-RNA polymerase holoenzyme confirmed the σBdependency of two of these genes and strongly suggested that two other genes, encoding an oligopeptide-binding OppA-like protein and subunit II of the cytochromedubiquinol oxidase, are also σBdependent. In conclusion, σBofB. cereusnot only regulates genes directly involved in the stress response but may also control specific metabolic rearrangements.