Vibrio cholerae Response Regulator VxrB Controls Colonization and Regulates the Type VI Secretion System.

Andrew T Cheng,Fitnat H Yildiz,Karen M Ottemann,Andreas J Baumler

doi:10.1371/journal.ppat.1004933

Andrew T Cheng, Fitnat H Yildiz + Show 2 more

Open Access

https://doi.org/10.1371/journal.ppat.1004933

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Journal: PLoS pathogens	Publication Date: May 22, 2015
Citations: 119	License type: CC BY 4.0

Affiliation: University of California, Santa Cruz

Abstract

Two-component signal transduction systems (TCS) are used by bacteria to sense and respond to their environment. TCS are typically composed of a sensor histidine kinase (HK) and a response regulator (RR). The Vibrio cholerae genome encodes 52 RR, but the role of these RRs in V. cholerae pathogenesis is largely unknown. To identify RRs that control V. cholerae colonization, in-frame deletions of each RR were generated and the resulting mutants analyzed using an infant mouse intestine colonization assay. We found that 12 of the 52 RR were involved in intestinal colonization. Mutants lacking one previously uncharacterized RR, VCA0566 (renamed VxrB), displayed a significant colonization defect. Further experiments showed that VxrB phosphorylation state on the predicted conserved aspartate contributes to intestine colonization. The VxrB regulon was determined using whole genome expression analysis. It consists of several genes, including those genes that create the type VI secretion system (T6SS). We determined that VxrB is required for T6SS expression using several in vitro assays and bacterial killing assays, and furthermore that the T6SS is required for intestinal colonization. vxrB is encoded in a four gene operon and the other vxr operon members also modulate intestinal colonization. Lastly, though ΔvxrB exhibited a defect in single-strain intestinal colonization, the ΔvxrB strain did not show any in vitro growth defect. Overall, our work revealed that a small set of RRs is required for intestinal colonization and one of these regulators, VxrB affects colonization at least in part through its regulation of T6SS genes.

Highlights

Vibrio cholerae causes the diarrheal disease cholera that affects 3 to 5 million people worldwide every year, resulting in 100,000–120,000 deaths annually [1]
transduction systems (TCS) consists of a histidine kinase (HK), which senses environmental signals, and a corresponding response regulator (RR), which mediates a cellular response
The genome of the human pathogen V. cholerae contains a multitude of genes encoding HKs and RRs proteins

Summary

Introduction

Vibrio cholerae causes the diarrheal disease cholera that affects 3 to 5 million people worldwide every year, resulting in 100,000–120,000 deaths annually [1]. V. cholerae produces a number of virulence factors which facilitate colonization of the intestine and subsequent disease. Major virulence factors are cholera toxin (CT), which is responsible for production of profuse watery diarrhea, and a type IV pilus called the toxin-coregulated pilus (TCP), which is required for intestinal colonization [2]. V. cholerae virulence factors are well known to be under extensive transcriptional control. CT and TCP production are controlled by the transcriptional activator ToxT [3, 4]. Expression of toxT, in turn, is controlled by a virulence regulatory cascade involving the membrane-bound transcriptional activators ToxRS and TcpPH. These two regulators activate toxT transcription directly [5,6,7]. The quorum sensing (QS) regulatory system is linked to the virulence gene regulatory cascade through HapR, the master QS regulator, which represses aphA expression [10]

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