Yersinia ruckeri is a fish pathogen, causing an infection called enteric redmouth disease that affects mostly salmonid fish. The disease causes significant losses in the aquaculture industry. Like most bacteria, Y. ruckeri survives in the environment by forming biofilms. These are multicellular bacterial communities embedded in a slimy extracellular matrix composed of a variety of different molecules.
In their newly published study, Jack C. Leo and colleagues investigated the role of two surface proteins in biofilm formation in Y. ruckeri – Y. ruckeri invasin (YrInv) and Y. ruckeri invasin-like molecule (YrIlm). They had identified these proteins previously and, based on their similarity to adhesins from other bacteria, assumed both mediated attachment of Y. ruckeri to surfaces.
Knocking out the genes coding for these proteins individually significantly reduced the ability of Y. ruckeri to form a biofilm on several different types of surface, including many used in aquaculture (PVC, steel and polystyrene). When both genes were knocked out, Y. ruckeri barely formed any biofilm.
Larvae of the greater waxmoth (Galleria mellonella) were used to test whether YrInv and YrIlm also played a role in causing disease. Y. ruckeri strains unable to produce one or both proteins had to be used at much higher infectious doses than the wild-type strain to kill the larvae.
Overall, this study demonstrates that YrInv and YrIlm are adhesins of Y. ruckeri that promote biofilm formation and virulence. As such, they are potential targets for vaccine development or measures to control biofilm formation by Y. ruckeri in an aquaculture setting.
Wrobel A, Saragliadis A, Pérez-Ortega J, et al. The inverse autotransporters of Yersinia ruckeri, YrInv and YrIlm, contribute to biofilm formation and virulence. Environ Microbiol. 2020;doi:10.1111/1462-2920.15051.