Regulation of the Bacillus subtilis bcrC Bacitracin Resistance Gene by Two Extracytoplasmic Function σ Factors

Abstract

ABSTRACT Bacitracin resistance is normally conferred by either of two major mechanisms, the BcrABC transporter, which pumps out bacitracin, or BacA, an undecaprenol kinase that provides C 55 -isoprenyl phosphate by de novo synthesis. We demonstrate that the Bacillus subtilis bcrC ( ywoA ) gene, encoding a putative bacitracin transport permease, is an important bacitracin resistance determinant. A bcrC mutant strain had an eightfold-higher sensitivity to bacitracin. Expression of bcrC initiated from a single promoter site that could be recognized by either of two extracytoplasmic function (ECF) σ factors, σ X or σ M . Bacitracin induced expression of bcrC , and this induction was dependent on σ M but not on σ X . Under inducing conditions, expression was primarily dependent on σ M . As a consequence, a sigM mutant was fourfold more sensitive to bacitracin, while the sigX mutant was only slightly sensitive. A sigX sigM double mutant was similar to a bcrC mutant in sensitivity. These results support the suggestion that one function of B. subtilis ECF σ factors is to coordinate antibiotic stress responses.