Oyster aquaculture farms and restoration projects provide food, economic growth, habitat to other species, and coastal resilience to flooding, storm effects, and erosion. Hatcheries are critical in producing oyster seed required for a rapidly growing aquaculture industry and the restoration of dwindling populations in wild ecosystems. Vibriosis, a major disease caused by various pathogenic Vibrio species, affects oysters and other bivalves at the larval stage and has a significant impact on seed production by shellfish hatcheries. A commercial line of a marine probiont, Phaeobacter inhibens S4 (S4), has been developed to prevent vibriosis in oyster hatcheries. However, there is a large variation in the effectiveness of probiont S4 when used in shellfish hatcheries.
The goal of this project was to evaluate the potential effect of bacteriophages on probiont-pathogen interactions, including boosting or decreasing probiotic action. Lytic vibriophages vB_VcorM-Gr11A (11A) and vB_VcorM-Gr28A (28A) were tested against pathogen Vibrio coralliilyticus RE22, probiont Phaeobacter inhibens S4, and other bacterial pathogens recently isolated from bivalve larvae, including a highly pathogenic Vibrio neptunius strain. These phages showed lytic activity towards both RE22 and S4. Biofilm formation was reduced in RE22 but increased in S4, suggesting phages can modulate processes involved in probiont-pathogen interactions. Furthermore, phages 11A and 28A increased biofilm formation by candidate probiont Glutamicibacter soli and decreased biofilm formation by candidate probiont Pseudoalteromonas galatheae in a temperature-dependent fashion. Two other phages were isolated from water collected at bivalve hatcheries and showed lytic or lysogenic activity against V. coralliilyticus RE22 and P. inhibens S4. Functional and genomic characterization of the newly isolated phages is underway. This information will be useful in formulating targeted cocktails of probionts/phages with increased efficacy in the complex microbial environments of shellfish hatcheries.