The consumption and value of the eastern oyster (Crassostrea virginica) and pacific oyster (Crassostrea gigas) has increased dramatically in the last 15 years. The fisheries industry relies upon
aquaculture to meet the commercial demand for oysters. Pathogen outbreaks of Vibrio spp. can have devastating effects on oyster production in shellfish hatcheries. Currently,
probiotics are being explored as new treatments to combat the threat of infectious
diseases. We recently isolated a probiotic bacterium belonging to the genus Phaeobacter from the inner side of the shell of a healthy oyster in Rhode Island. This bacterium
significantly protects oyster larvae against infection by the shellfish pathogens
V. tubiashii and R. crassostreae in vivo. A chemical investigation of the bacterium using HPLC-UV-bioassay, semi-preparative
HPLC, MS, IR, and NMR yielded a tropolone antibiotic. Four knock-out genetic mutants
were constructed to investigate the role of the tropolone in the probiotic protective
effect. Chemical analysis of bacterial supernatants confirmed that the mutants lacked
the ability to produce the tropolone. In vivo assays conducted with the mutant strains demonstrate that production of the tropolone
antibiotic is required for the probiotic effects of this strain.
