|CHURCH, KARLEE - Rutgers University|
|HASE, CLAUDIA - Oregon State University|
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/2014
Publication Date: 12/11/2014
Citation: Richards, G.P., Watson, M.A., Needleman, D.S., Church, K.M., Hase, C.C. 2014. Mortalities of eastern and pacific oyster larvae caused by the pathogens Vibrio coralliilyticus and Vibrio tubiashii. Applied and Environmental Microbiology. 81:292-297.
Interpretive Summary: Larval shellfish mortalities have plagued oyster and clam hatcheries in the United States and elsewhere. One bacterium that has been associated with the illnesses is the shellfish pathogen Vibrio tubiashii. Another bacterium more recently recognized as a pathogen of some shellfish species is Vibrio coralliilyticus, which also causes coral bleaching, a disease of corals which has decimated coral reefs in many parts of the world. We evaluated the ability of two strains of V. tubiashii and four strains of V. coralliilyticus to infect Eastern and Pacific oyster larvae. We showed for the first time that both strains of V. tubiashii readily killed healthy Eastern oyster larvae, but not healthy Pacific oyster larvae. In comparison, the four V. coralliilyticus isolates killed both Eastern and Pacific oyster larvae. Some isolates caused more mortalities than others. Although V. tubiashii has been associated with major hatchery crashes in the Pacific Northwest, most of these isolates were misidentified and were actually V. coralliilyticus. Thus, the problems with larval mortalities on the U.S. West Coast appear to be more from V. coralliilyticus than from V. tubiashii. This information may facilitate a more targeted response to future, hatchery-associated outbreaks of shellfish disease.
Technical Abstract: Vibrio tubiashii is reported to be a bacterial pathogen of larval Eastern oysters (Crassostrea virginica) and Pacific oysters (Crassostrea gigas) and has been associated with major hatchery crashes, causing shortages in seed oysters for commercial shellfish producers. Another bacterium, Vibrio coralliilyticus, a well-known coral pathogen, has recently been found to elicit mortalities in a variety of fish and shellfish. Several strains of V. coralliilyticus, like American Type Culture Collection (ATCC) strain 19105, and Pacific isolates RE22 and RE98, were until recently misidentified as V. tubiashii. We compared the mortalities caused by two V. tubiashii and four V. coralliilyticus strains in Eastern and Pacific oyster larvae. The LD50 of V. coralliilyticus in Eastern oysters ranged from 1.1 x 10e4 to 3.0 x 10e4 CFU/ml seawater, with strains RE98 and RE22 being the most virulent. This study shows for the first time that V. coralliilyticus causes disease in Eastern oyster larvae. Results in Pacific oysters were similar with LD50’s between 1.2 x 10e4 and 4.0 x 10e4 CFU/ml. Vibrio tubiashii ATCC 19106 was highly infectious toward Eastern oyster larvae (LD50 = 3.8 x 10e3 CFU/ml), but was essentially non-pathogenic toward Pacific oysters at a dosage of 1.1 x 10e4 CFU/ml. This data, coupled with the fact that many isolates originally thought to be V. tubiashii are actually V. coralliilyticus, suggests that V. coralliilyticus has been a more significant pathogen to larval bivalve shellfish than V. tubiashii, particularly on the US West Coast, and may have contributed to substantial hatchery-associated morbidity and mortality in recent years.