The EnvZ-OmpR Two-Component Signaling System Is Inactivated in a Mutant Devoid of Osmoregulated Periplasmic Glucans in Dickeya dadantii.

Peggy Gruau,Marine Caby,Edwige Madec,Brigitte Delrue,Jean-Marie Lacroix,Sébastien Bontemps-Gallo

doi:10.3389/fmicb.2018.02459

Abstract

Osmoregulated periplasmic glucans (OPGs) are general constituents of alpha-, beta-, and gamma-Proteobacteria. This polymer of glucose is required for full virulence of many pathogens including Dickeya dadantii (D. dadantii). The phytopathogenic enterobacterium D. dadantii causes soft-rot disease in a wide range of plants. An OPG-defective mutant is impaired in environment sensing. We previously demonstrated that (i) fluctuation of OPG concentration controlled the activation level of the RcsCDB system, and (ii) RcsCDB along with EnvZ/OmpR controlled the mechanism of OPG succinylation. These previous data lead us to explore whether OPGs are required for other two-component systems. In this study, we demonstrate that inactivation of the EnvZ/OmpR system in an OPG-defective mutant restores full synthesis of pectinase but only partial virulence. Unlike for the RcsCDB system, the EnvZ-OmpR system is not controlled by OPG concentration but requires OPGs for proper activation.

Highlights

Osmoregulated periplasmic glucans (OPGs), β-D-glucans oligosaccharides, are major envelope components found in the periplasm of almost all proteobacteria
We have shown that RcsCDB and OPG are tightly connected: (i) fluctuation of OPG concentration controls the activation level of the RcsCDB system (BontempsGallo et al, 2013), and (ii) RcsCDB, along with the twocomponent system EnvZ/OmpR, controls the mechanism of OPG succinylation (Bontemps-Gallo et al, 2016)
To show whether two-component system dysfunction is a general feature of bacteria lacking OPGs, we investigated the potential relationship between another two-component system and OPGs

Summary

Introduction

Osmoregulated periplasmic glucans (OPGs), β-D-glucans oligosaccharides, are major envelope components found in the periplasm of almost all proteobacteria. Their concentration increases as the osmolarity of the medium decreases (Kennedy, 1996; Bohin and Lacroix, 2006; Bontemps-Gallo et al, 2017). The opgG and opgH mutant strains are completely devoid of OPGs (Bontemps-Gallo et al, 2017). D. dadantii, the agent of soft rot disease, is directly responsible for 5 to 25% of potato crop loss in Europe and Israel (Toth et al, 2011) This phytopathogen is listed as an A2 quarantine organism by the European and Mediterranean Plant Protection Organization

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