The Probiotic Bacterium Phaeobacter inhibens Downregulates Virulence Factor Transcription in the Shellfish Pathogen Vibrio coralliilyticus by N -Acyl Homoserine Lactone Production

Probiotics represent a promising alternative strategy to control infection and disease caused by marine pathogens of aquaculturally important species. Generally, the beneficial effects of probiotics include improved water quality, control of pathogenic bacteria and their virulence, stimulation of the immune system, and improved animal growth. Previously, we isolated a probiotic bacterium,Phaeobacter inhibens S4Sm, which protects oyster larvae fromVibrio coralliilyticus RE22Sm infection. We also demonstrated that both antibiotic secretion and biofilm formation play important roles in S4Sm probiotic activity. Here, we report thatP. inhibens S4Sm, an alphaproteobacterium and member of theRoseobacter clade, also secretes secondary metabolites that hijack the quorum sensing ability ofV. coralliilyticus RE22Sm, suppressing virulence gene expression. This finding demonstrates that probiotic bacteria can exert their host protection by using a multipronged array of behaviors that limit the ability of pathogens to become established and cause infection.