DsbA and MgrB Regulate steA Expression through the Two-Component System PhoQ/PhoP in Salmonella enterica

Abstract

ABSTRACT SteA is a protein that can be translocated into host cells through the two virulence-related type III secretion systems that are present in Salmonella enterica . We used the T-POP system to carry out general screens for loci that exhibited activation or repression of a steA :: lacZ fusion. These screens identified the histidine kinase PhoQ and the response regulator PhoP as positive regulators of steA . Transcription of this gene is σ70 dependent, and the promoter of steA contains a PhoP-binding site that mediates direct regulation by PhoP. Our screens also detected MgrB (also known as YobG) as a negative regulator of the expression of steA . Disruption of the gene encoding the periplasmic disulfide oxidoreductase DsbA or addition of the reducing agent dithiothreitol increases transcription of steA . The effects of MgrB and DsbA on steA are mediated by PhoP. These results suggest that the cellular redox status is a factor contributing to regulation of steA and, probably, other virulence genes regulated by the PhoQ/PhoP two-component system.