Response of Bacillus subtilis to nitric oxide and the nitrosating agent sodium nitroprusside

We examined the effects of nitric oxide (NO) and sodium nitroprusside (SNP) on Bacillus subtilis physiology and gene expression. In aerobically growing cultures, cell death was most pronounced when NO gas was added incrementally rather than as a single bolus, suggesting that the length of exposure was important in determining cell survival. DNA microarrays, Northern hybridizations, and RNA slot blot analyses were employed to characterize the global transcriptional response of B. subtilis to NO and SNP. Under both aerobic and anaerobic conditions the gene most highly induced by NO was hmp, a flavohemoglobin known to protect bacteria from NO stress. Anaerobically, NO also induced genes repressed by the Fe(II)-containing metalloregulators, Fur and PerR, consistent with the known ability of NO to nitrosylate the Fe(II) center in Fur. In support of this model, we demonstrate that NO fails to induce PerR-regulated genes under growth conditions that favor the formation of PerR:Mn(II) rather than PerR:Fe(II). Aerobically, NO gas induced hmp, the sigmaB general stress regulon, and, to a lesser extent, the Fur and PerR regulons. Surprisingly, NO gas induced the sigmaB regulon via the energy branch of the sigmaB regulatory cascade while induction by SNP was mediated by the environmental stress branch. This emphasizes that NO and SNP elicit genetically distinct stress responses.