A new player in bacterial sulfide-inducible transcriptional regulation.

Although hydrogen sulfide (H(2) S) is perhaps best known as a toxic gas, the electron-rich H(2) S functions as an energy source and electron donor for chemolithotrophic and photosynthetic bacteria, via sulfide oxidation, and is a universal substrate for cysteine biosynthesis. These distinct harmful and beneficial roles of H(2) S suggest the need to 'sense' prevailing concentrations of sulfide and downstream reactive sulfur species (RSS) and regulate the expression of genes mediating sulfide homeostasis. The paper by Li et al. in this issue of Molecular Microbiology adds Cupriavidus FisR to an expanding repertoire of regulatory mechanisms that bacteria have evolved to sense cellular RSS and mitigate their deleterious effects.