A novel hybrid kinase is essential for activating the sigmaB-mediated stress response of Bacillus cereus

(1) Laboratory of Food Microbiology, Wageningen University and Research Centre, P.O. Box 8129, 6700 EV Wageningen, The Netherlands (2) TI Food and Nutrition (TIFN), Wageningen (3) Centre for Molecular and Biomolecular Informatics (CMBI), NCMLS, Radboud University Nijmegen Medical Centre, Nijmegen (4) NIZO food research BV, Ede (5) Food Technology Centre, Wageningen University and Research Centre (6) Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands A common bacterial strategy for monitoring environmental challenges is to use two-component signal transduction systems (TCS), which consist of a sensor histidine kinase (HK) and a response regulator (RR). In the food-borne pathogen Bacillus cereus, the alternative sigma factor sB is activated by the unique RR RsbY. Here we present evidence that the PP2C-type phosphatase RsbY receives its input signals from the complex, multisensor hybrid kinase BC1008 (renamed RsbK). Genomics analyses revealed that rsbY is located in a conserved gene cluster including rsbK. An rsbK deletion strain was shown to be incapable of inducing sB protein levels upon mild stress conditions and was impaired in its heat adaptive response. Comparison of the wild-type and rsbK mutant transcriptomes upon heat shock revealed that RsbK was primarily involved in the activation of the sB-mediated stress response. Truncation of the fused RsbK RR receiver domain demonstrated the importance of this domain for sB induction upon stress and indicated that this domain plays a role in fine-tuning RsbK kinase activity. The domain architecture of this unique sensory protein suggests that in the B. cereus group, environmental and intracellular stress signaling routes are combined into one single protein, thus markedly differing from known sB activation pathways in related low-GC Gram-positives.