Dickeya dadantii: towards understanding the biological role of OPGs

Osmoregulated periplasmic glucans (OPGs) are glucose oligomers. D. dadantii, a phytopathogen with a broad host range, causes soft rot disease. In this bacterium, a mutant lacking OPG shows a pleiotropic phenotype: total loss of virulence, decreased motility, and general induction of a stress response suggesting a severe defect in environmental perception. This idea is reinforced by the link between two-component systems, which are key systems for environmental perception, and OPGs. An exploratory approach to the role of OPGs in virulence has shown that in a mutant lacking OPG, inactivation of pecS, the main repressor of virulence, restores virulence on endive leaves. The conservation of several phenotypes associated with the defect in OPG synthesis indicates that the two mutations do not affect a single regulatory pathway. Finally, the identification of the gene encoding the enzyme responsible for OPG succinylation has completed the set of genes involved in OPG biosynthesis.