The quorum sensing system with 3-hydroxymyristate as a quorum sensing signal is implicated in biofilm formation by Ralstonia solanacearum strain OE1-1, leading to its virulence
1Kochi univ., 2Osaka Pref. Univ.
Ralstonia solanacearum strain AW1 reportedly produces methyl 3-hydroxypalmitate (3-OH PAME) as a quorum sensing (QS) signal, of which production is dependently on the phcB gene encoding methyltransferase. However, 3-OH PAME does not exert to function PhcA, which regulate expression of many virulence-related genes, through the QS in R. solanacearum strain OE1-1 (OE1-1). In this study, we first identified a novel QS signal from OE1-1. The secondary metabolite profiles of OE1-1 and the phcB gene deletion mutant (ΔphcB) showed production of methyl 3-hydroxymyristate (3-OH MAME) but not 3OH-PAME by OE1-1, dependent on the phcB gene. The phcB gene deletion resulted in a significant reduction of exopolysaccharide (EPS) production, which is positively regulated by functioned PhcA and an indicator for the QS. Furthermore, application with 3-OH MAME but not 3-OH PAME recovered EPS production by the ΔphcB. These results showed that 3-OH MAME exerts as the QS signal in OE1-1. Biofilm formation by OE1-1 is required for its colonization in intercellular spaces after invasion into host roots, leading to its virulence. The ΔphcB produced biofilms significantly less than OE1-1, and lost its virulence. Furthermore, application with 3-OH MAME recovered its biofilm formation. These results showed that the QS with 3-OH MAME is involved in biofilm formation by OE1-1, leading to its virulence. The GC/MS analysis of EtOAc extracts from additional 8 strains of R. solanacearum showed that 3 strains and 5 strains produce 3-OH PAME and 3-OH MAME, respectively. The phylogenetic analysis of deduced amino acid sequences of PhcB protein among these strains including OE1-1 and AW1 showed clusters corresponding to their 3-OH MAME/3-OH PAME productivity, independent of their phylotypes. These results demonstrate that 3-OH MAME is another crucial QS signal and also highlight the unique evolution of QS systems in R. solanacearum strains corresponding to their virulence.
keywords:*Ralstonia solanacearum*,quorum sensing,virulence