Bacteriophages against Vibrio coralliilyticus and Vibrio tubiashii: Isolation, Characterization, and Remediation of Larval Oyster Mortalities.

and are pathogens responsible for high larval oyster mortality rates in shellfish hatcheries. Bacteriophage therapy was evaluated to determine its potential to remediate these mortalities. Sixteen phages against and were isolated and characterized from Hawaiian seawater. Fourteen isolates were members of the family, and two were members of the In proof-of-principle trials, a cocktail of five phages reduced mortalities of larval Eastern oysters () and Pacific oysters () by up to 91% 6 days after challenge with lethal doses of Larval survival depended on the oyster species, the quantities of phages and vibrios applied, and the species and strain of A later-generation cocktail, designated VCP300, was formulated with three lytic phages subsequently named phages vB_VcorM-GR7B, vB_VcorM-GR11A, and vB_VcorM-GR28A (abbreviated 7B, 11A, and 28A, respectively). Together, these three phages displayed host specificity toward eight strains and a strain. Larval mortalities from strains RE98 and OCN008 were significantly reduced by >90% (< 0.0001) over 6 days with phage treatment compared to those of untreated controls. Genomic sequencing of phages 7B, 11A, and 28A revealed 207,758-, 194,800-, and 154,046-bp linear DNA genomes, respectively, with the latter showing 92% similarity to phage YC, a strain from the Great Barrier Reef, Australia. Phage 7B and 11A genomes showed little similarity to phages in the NCBI database. This study demonstrates the promising potential for phage therapy to reduce larval oyster mortalities in oyster hatcheries. Shellfish hatcheries encounter episodic outbreaks of larval oyster mortalities, jeopardizing the economic stability of hatcheries and the commercial shellfish industry. Shellfish pathogens like and have been recognized as major contributors of larval oyster mortalities in U.S. East and West Coast hatcheries for many years. This study isolated, identified, and characterized bacteriophages against these species and demonstrated their ability to reduce mortalities from in larval Pacific oysters and from both and in larval Eastern oysters. Phage therapy offers a promising approach for stimulating hatchery production to ensure the well-being of hatcheries and the commercial oyster trade.