A pmrA Constitutive Mutant Sensitizes Escherichia coli to Deoxycholic Acid

Abstract

ABSTRACT An Escherichia coli mutant was isolated and shown to be polymyxin B resistant. Mapping and sequence analysis revealed a missense mutation at codon 53 within the pmrA ( basR ) gene that results in a G-to-V substitution. Fusions of promoters from the pmrC , yibD , and pmrH genes with the lacZ reporter showed that they were constitutively expressed in pmrA53 cells. In pmrA + strains, these promoters were induced by iron and zinc, while a Δ pmrA mutation blocked induction. The PmrA regulon regulates genes whose products remodel the composition and charge of lipid A and hence the barrier properties of the outer membrane. Along these lines, the pmrA53 mutant was also found to be hypersensitive to the anionic bile detergent deoxycholic acid.