Transcriptome analyses of 2.5% and 5% NaCl-stressed B. cereus ATCC 14579

Bacteria are able to cope with the challenges of sudden increase of salinity by activating adaptation mechanisms. In this study, exponentially growing cells of the food-borne pathogen Bacillus cereus ATCC 14579 were exposed to both mild (2.5% NaCl w/v) and severe (5% NaCl w/v) salt stress conditions. B. cereus continued growth at a reduced rate when shifted to mild salt stress. Exposure to severe salt stress resulted in a lag period, and after 60 min cellular growth was resumed filamentously. Whole-genome expression analyses of cells exposed to 2.5% salt stress revealed an overlap with that of cells exposed to 5% salt stress, suggesting that the corresponding genes (n = 147) were involved in a general salt stress response. Up-regulation of osmolyte, Na+/H+ and di-/tripeptide transporters and activation of an oxidative stress response were important aspects of this general salt stress response. Activation of this response may confer cross-protection towards other stresses, and increased resistance to heat and H2O2 was indeed observed. Notably, a temporal shift was observed between the observed transcriptome and phenotype responses of severely salt-stressed cells including cellular filamentation, reduced chemotaxis performance, catalase activity and optimal oxidative stress resistance. The linkage of transcriptomes and phenotypic characteristics can contribute to a better understanding of cellular stress adaptation strategies and possible cross protection mechanisms.