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J. Bacteriol. doi:10.1128/JB.00313-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Identification of the ^B-regulon of Bacillus cereus and conservation of ^B-regulated genes in low-GC gram-positive bacteria

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

^* To whom correspondence should be addressed. Email: tjakko.abee{at}wur.nl.

	Abstract

The alternative sigma factor ^B has an important role in the acquisition of stress-resistance in many gram-positive bacteria including the foodborne 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 deleted for 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-positives. The data described in this study and earlier 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-positives. 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-positives has evolved to perform niche-specific functions.

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