SwrA as global modulator of the two-component system DegS/U in B. subtilis

Abstract

The two-component system DegS/U of Bacillus subtilis controls more than one hundred genes involved in several different cellular behaviours. Since the consensus sequence recognized by the response regulator DegU has not been clearly defined yet, mutations in either component have been crucial in the identification of the cellular targets of this regulatory system. Over the years, the degU32Hy mutant allele, that was supposed to mimic the activated regulator, has been commonly used to define the impact of this TCS on its regulated genes in domestic strains. SwrA encodes a small protein essential for swarming motility and for poly-{gamma}-glutamate biosynthesis and is only present in wild strains. Previous work indicated that SwrA is partnering with DegU~P in exerting its role on both phenotypes. In this work, inserting a degS200Hy mutation in swrA+ and swrA- isogenic strains we demonstrate that SwrA modulates the action of DegU~P on two new phenotypes, subtilisin expression and competence for DNA uptake, with a remarkable effect on transformation. These effects cannot not be appreciated with the DegU32Hy mutant as it does not mirror the wild-type DegU protein in its ability to interact with SwrA.