The opgC gene is required for OPGs succinylation and is osmoregulated through RcsCDB and EnvZ/OmpR in the phytopathogen Dickeya dadantii.

Sébastien Bontemps-Gallo,Jacqueline Dondeyne,Jean-Marie Lacroix,Erika Souche,Edwige Madec,Catherine Robbe-Masselot

doi:10.1038/srep19619

Abstract

Osmoregulated periplasmic glucans (OPGs) are a family of periplasmic oligosaccharides found in the envelope of most Proteobacteria. They are required for virulence of zoo- and phyto-pathogens. The glucose backbone of OPGs is substituted by various kinds of molecules depending on the species, O-succinyl residues being the most widely distributed. In our model, Dickeya dadantii, a phytopathogenic bacteria causing soft rot disease in a wide range of plant species, the backbone of OPGs is substituted by O-succinyl residues in media of high osmolarity and by O-acetyl residues whatever the osmolarity. The opgC gene encoding a transmembrane protein required for the succinylation of the OPGs in D. dadantii was found after an in silico search of a gene encoding a protein with the main characteristics recovered in the two previously characterized OpgC of E. coli and R. sphaeroides, i.e. 10 transmembrane segments and one acyl-transferase domain. Characterization of the opgC gene revealed that high osmolarity expression of the succinyl transferase is controlled by both the EnvZ-OmpR and RcsCDB phosphorelay systems. The loss of O-succinyl residue did not affect the virulence of D. dadantii, suggesting that only the glucose backbone of OPGs is required for virulence.

Highlights

Dickeya dadantii is a phytopathogenic Enterobacteria that causes soft rot disease in a wide range of plant species, including crops[1]
In our attempt to identify the opgC gene in Dickeya dadantii, we first looked unsuccessfully for an homologous gene of opgC from E. coli or R. sphaeroides in the D. dadantii genome
We looked for a gene encoding a protein with the two main characteristics found in the OpgC of E. coli and R. sphaeroides, i.e. 10 transmembrane segments and an acyl-transferase domain

Summary

Introduction

Dickeya dadantii is a phytopathogenic Enterobacteria that causes soft rot disease in a wide range of plant species, including crops[1]. In D. dadantii, opgG and opgH mutant strains are completely devoid of OPGs and exhibit pleiotropic phenotypes including a total loss of virulence, loss of motility, increased synthesis of exopolysaccharides and induction of a general stress response indicating impairment in the perception of the environment[12,13]. Most of these phenotypic characteristics are the result of the requirement of OPGs to achieve a low level of activation of the RcsCDB two-component signalling pathways[14,15,16]. In several Enterobacteria, such as D. dadantii, it was shown that activation of the RcsCDB system enhanced exopolysaccharide synthesis, cell division and decreased virulence and motility[15,19,20,21]

Methods

Results

Conclusion