The two-component regulatory system BacRS is associated with bacitracin 'self-resistance' of Bacillus licheniformis ATCC 10716

Bacitracin is a peptide antibiotic produced by several Bacillus licheniform is strains that is most active against other Gram-positive microorganisms, but not against the producer strain itself. Recently, heterologous expressi on of the bacitracin resistance mediating BcrABC transporter in Bacillus su btilis and Escherichia coli was described. In this study we could determine that the transporter encoding bcrABC genes are localized about 3 kb downst ream of the 44-kb bacitracin biosynthetic operon bacABC. Between the bac op eron and the bcrABC genes two orfs, designated bacR and bacS, were identifi ed. They code for proteins with high homology to regulator and sensor prote ins of two-component systems. A disruption mutant of the bacRS genes was co nstructed. While the mutant displayed no effects on the bacitracin producti on it exhibited highly increased bacitracin sensitivity compared to the wil d-type strain. Western blot analysis of the expression of BcrA, the ATP-bin ding cassette of the transporter, showed in the wild-type a moderate BcrA i nduction in late stationary cells that accumulate bacitracin, whereas in th e bacRS mutant cells the BcrA expression was constitutive. A comparison of bacitracin stressed and nonstressed wild-type cells in Western blot analysi s revealed increasing amounts of BcrA and a decrease in BacR in the stresse d cells. From these findings we infer that BacR acts as a negative regulato r for controlling the expression of the bcrABC transporter genes.