Bacteriophages improve survival and metamorphosis of larval Pacific oysters (Crassostrea gigas) exposed to Vibrio coralliilyticus (strain RE98)

Authors: MADISON, DAVID - Oregon State University; Richards, Gary; SULAKVELIDZE, ALEXANDER - Intralytix, Inc; LANGDON, CHRIS - Oregon State University

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2022
Publication Date: 4/11/2022
Citation: Madison, D., Richards, G.P., Sulakvelidze, A., Langdon, C. 2022. Bacteriophages improve survival and metamorphosis of larval Pacific oysters (Crassostrea gigas) exposed to Vibrio coralliilyticus (strain RE98). Aquaculture. 555(2022)738242. https://doi.org/10.1016/j.aquaculture.2022.738242.
DOI: https://doi.org/10.1016/j.aquaculture.2022.738242

Interpretive Summary: The U.S. oyster industry relies on hatcheries to produce seed oysters for commercial planting operations, but hatcheries are vulnerable to large-scale larval mortality events. The bacterial pathogen Vibrio coralliilyticus has been implicated in several of these large-scale mortality events, highlighting the need to control V. coralliilyticus in oyster hatcheries. This study evaluated the impact of a cocktail of phages over the entire larval culture period from the early D-stage larvae through metamorphosis. It demonstrated that phage treatment can reduce larval oyster mortality due to exposure to lethal concentrations of V. coralliilyticus and can improve metamorphosis success, potentially providing a means of increasing hatchery production of seed oysters.

Technical Abstract: The bacterial pathogen Vibrio coralliilyticus has been implicated in severe larval oyster mortality events in U.S. hatcheries. The aims of this study were to determine whether additions of bacteriophages (phages) specific to V. coralliilyticus strain RE98 can lower concentrations of V. coralliilyticus in seawater and consequently enhance survival, growth and metamorphosis of larvae of the Pacific oyster (Crassostrea gigas). Cocktails containing 2 or 3 previously characterized phages in the family Myoviridae (designated 6B, 7B and 11A) were added to cultures of C. gigas larvae together with V. coralliilyticus RE98. Results confirmed that: 1) the addition of a 2-phage cocktail (6B and 11A) significantly reduced concentrations of V. coralliilyticus in autoclaved seawater over a 48-h period in the absence of larvae (p<0.05); 2) the concentration of a 2-phage cocktail required to significantly reduce mortality of 2-day post fertilization (PF) larvae depended on the initial concentration of V. coralliilyticus added to the seawater; 3) preparation of three-phage cocktails using tangential flow filtration increased the effectiveness of the phages compared to 0.2-um filtration; and 4) a single addition of a cocktail containing 3 phages to two-day old oyster larval cultures eliminated mortality due to exposure to V. coralliilyticus (>99% mortality without phages) and significantly improved the proportion of larvae metamorphosing to become spat more than 16 days later (p<0.05). Reductions in larval mortality were consistent across a range of culture conditions, varying from 1 ml cultures with autoclaved seawater to 10-liter cultures supplied with non-sterile, 10-um filtered seawater.