B was found to play a role in the protective heat shock response of B. cereus. The sigB null mutant was less protected against the lethal temperature of 50°C by a preadaptation to 42°C than the parent strain was, resulting in a more-than-100-fold-reduced survival of the mutant after 40 min at 50°C.

This paper describes the molecular responses of Lactobacillus plantarum WCFS1 toward ethanol exposure. Global transcriptome profiling using DNA microarrays demonstrated adaptation of the microorganism to the presence of 8% ethanol over short (10-min and 30-min) and long (24-h) time intervals. A total of 57 genes were differentially expressed at all time points. Expression levels of an additional 859 and 873 genes were modulated after 30 min and 24 h of exposure to the solvent, respectively. Ethanol exposure led to induced expression of genes involved in citrate metabolism and cell envelope architecture, as well as canonical stress response pathways controlled by the central stress regulators HrcA and CtsR. Correspondingly, cells grown for 24 h in medium containing 8% ethanol exhibited higher levels of citrate consumption and modified cell membrane fatty acid composition and showed invaginating septa compared with cells grown in liquid medium without ethanol. In addition, these physiological changes resulted in cross-protection against high temperatures but not against several other stresses tested. To evaluate the role of HrcA and CtsR in ethanol tolerance, ctsR and hrcA gene deletion mutants were constructed. The growth rate of the L. plantarum ⌬ctsR::cat strain was impaired in de Man-Rogosa-Sharpe (MRS) medium containing 8% ethanol, whereas growth of the L. plantarum ⌬hrcA::cat and ⌬ctsR ⌬hrcA::cat mutants was indistinguishable from that of wild-type cells. Overall, these results suggest that the induction of CtsR class III stress responses provides cross-protection against heat stress.

No abstract

A common bacterial strategy for monitoring environmental challenges is to use two-component systems, which consist of a sensor histidine kinase (HK) and a response regulator (RR). In the food-borne pathogen Bacillus cereus, the alternative sigma factor sigma(B) is activated by the RR RsbY. Here we present strong indications that the PP2C-type phosphatase RsbY receives its input from the multi-sensor hybrid kinase BC1008 (renamed RsbK). Genome analyses revealed that, across bacilli, rsbY and rsbK are located in a conserved gene cluster. A B. cereus rsbK deletion strain was shown to be incapable of inducing sigma(B) upon 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 sigma(B)-mediated stress response. Truncation of the RsbK RR receiver domain demonstrated the importance of this domain for sigma(B) induction upon stress. The domain architecture of RsbK suggests that in the B. cereus group and in other bacilli, environmental and intracellular stress signalling routes are combined into one single protein. This strategy is markedly different from the sigma(B) activation pathway in other low-GC Gram-positives.

No abstract

The alternative sigma factor B is an important regulator of the stress response of Bacillus cereus. Here, the role of the regulatory proteins RsbV, RsbW, and RsbY in regulating B activity in B. cereus is analyzed. Functional characterization of RsbV and RsbW showed that they act as an anti-sigma factor antagonist and an anti-sigma factor, respectively. RsbW can also act as a kinase on RsbV. These data are in line with earlier functional characterizations of RsbV and RsbW homologs in B. subtilis. The rsbY gene is unique to B. cereus and its closest relatives and is predicted to encode a protein with an N-terminal CheY domain and a C-terminal PP2C domain. In an rsbY deletion mutant, the B response upon stress exposure was almost completely abolished, but the response could be restored by complementation with full-length rsbY. Expression analysis showed that rsbY is transcribed from both a A -dependent promoter and a B -dependent promoter. The central role of RsbY in regulating the activity of B indicates that in B. cereus, the B activation pathway is markedly different from that in other gram-positive bacteria.

respectively. In the latter condition a concomitant decrease in intracellular ATP levels 32 was observed. The transcriptome analyses revealed general and specific responses to 33 the acidulants used. The general acid stress response includes modulation of pyruvate 34 metabolism with activation of the butanediol fermentation pathway, and an oxidative 35 stress response that was, however, more extensive in the bacteriostatic and 36 bactericidal conditions. HL-specific and HAc-specific responses include modulation 37 of metabolic pathways for amino acid metabolism. Activation of lactate, formate, and 38 ethanol fermentation pathways, alternative electron-transport chain components and 39 fatty acid biosynthesis genes was noted in the presence of 15 mM undissociated HAc. 40In conclusion, our study has provided insights in phenotype-associated, and general 41 and acidulant-specific responses in B. cereus.

No abstract