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Identification of the ^B Regulon of Bacillus cereus and Conservation of ^B-Regulated Genes in Low-GC-Content Gram-Positive Bacteria ^,

Willem van Schaik,^1,2, Menno van der Voort,^1,2 Douwe Molenaar,^1,3 Roy Moezelaar,^1,4 Willem M. de Vos,¹ and Tjakko Abee^1,2*

Wageningen Centre for Food Sciences, P.O. Box 557, 6700AN Wageningen, The Netherlands,¹ Laboratory of Food Microbiology, Wageningen University and Research Centre, P.O. Box 8129, 6700EV Wageningen, The Netherlands,² NIZO Food Research, P.O. Box 20, 6710BA Ede, The Netherlands,³ Food Technology Centre, Wageningen University and Research Centre, P.O. Box 17, 6700AA Wageningen, The Netherlands⁴

Received 2 March 2007/ Accepted 29 March 2007

The alternative sigma factor ^B has an important role in the acquisition of stress resistance in many gram-positive bacteria, including the food-borne pathogen Bacillus cereus. Here, we describe the identification of the set of ^B-regulated genes in B. cereus by DNA microarray analysis of the transcriptome upon a mild heat shock. Twenty-four genes could be identified as being ^B dependent as witnessed by (i) significantly lower expression levels of these genes in mutants with a deletion of sigB and rsbY (which encode the alternative sigma factor ^B and a crucial positive regulator of ^B activity, respectively) than in the parental strain B. cereus ATCC 14579 and (ii) increased expression of these genes upon a heat shock. Newly identified ^B-dependent genes in B. cereus include a histidine kinase and two genes that have predicted functions in spore germination. This study shows that the ^B regulon of B. cereus is considerably smaller than that of other gram-positive bacteria. This appears to be in line with phylogenetic analyses where ^B of the B. cereus group was placed close to the ancestral form of ^B in gram-positive bacteria. The data described in this study and previous studies in which the complete ^B regulon of the gram-positive bacteria Bacillus subtilis, Listeria monocytogenes, and Staphylococcus aureus were determined enabled a comparison of the sets of ^B-regulated genes in the different gram-positive bacteria. This showed that only three genes (rsbV, rsbW, and sigB) are conserved in their ^B dependency in all four bacteria, suggesting that the ^B regulon of the different gram-positive bacteria has evolved to perform niche-specific functions.

Published ahead of print on 6 April 2007.

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

Present address: Toxines et Pathogénie Bacterienne, Institut Pasteur, Paris, France.

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