Bacillus subtilis is a metabolically versatile soil microbe and Gram-positive model organism that displays a sophisticated adaptive response to conditions of iron limitation. The endogenous siderophore of B. subtilis is bacillibactin, a trimeric catecholate siderophore similar in structure to enterobactin. In addition to bacillibactin, B. subtilis can obtain iron from several xenosiderophores, ferric citrate, heme, and through a newly discovered elemental iron permease.

The regulation of iron homeostasis in B. subtilis is complex and involves a ferric uptake regulator (Fur) protein as master regulator and at least two subsidiary regulatory systems. The most significant of these is an iron-sparing/prioritization response controlled by the small RNA FsrA and three auxiliary proteins (FbpABC). In addition, the bacillibactin uptake system is transcriptionally activated by an AraC family activator, Btr that directly senses bacillibactin. Iron uptake and homeostasis systems in B. anthracis and related organisms are largely similar to those in B. subtilis with some additional components. These include a second siderophore synthesis operon for petrobactin, which is important for virulence, and a more elaborate (or at least better understood) heme uptake system.

Further reading: Iron Uptake and Homeostasis in Microorganisms

Labels: bacillus, Iron acquisition mechanisms, Iron deficiency, Iron transporters, Iron uptake in Bacillus, Iron uptake systems, Iron-homeostasis, Iron-uptake, Siderophore, Siderophores