Genome-Wide Transcriptional Profiling Analysis of Adaptation ofBacillus subtilisto High Salinity

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Abstract
The gram-positive soil bacteriumBacillus subtilisoften faces increases in the salinity in its natural habitats. A transcriptional profiling approach was utilized to investigate both the initial reaction to a sudden increase in salinity elicited by the addition of 0.4 M NaCl and the cellular adaptation reactions to prolonged growth at high salinity (1.2 M NaCl). Following salt shock, asigBmutant displayed immediate and transient induction and repression of 75 and 51 genes, respectively. Continuous propagation of this strain in the presence of 1.2 M NaCl triggered the induction of 123 genes and led to the repression of 101 genes. In summary, our studies revealed (i) an immediate and transient induction of the SigW regulon following salt shock, (ii) a role of the DegS/DegU two-component system in sensing high salinity, (iii) a high-salinity-mediated iron limitation, and (iv) a repression of chemotaxis and motility genes by high salinity, causing severe impairment of the swarming capability ofB. subtiliscells. Initial adaptation to salt shock and continuous growth at high salinity share only a limited set of induced and repressed genes. This finding strongly suggests that these two phases of adaptation require distinctively different physiological adaptation reactions by theB. subtiliscell. The large portion of genes with unassigned functions among the high-salinity-induced or -repressed genes demonstrates that major aspects of the cellular adaptation ofB. subtilisto high salinity are unexplored so far.