Evaluating the potential of marine Bacteriovorax sp. DA5 as a biocontrol agent against vibriosis in Litopenaeus vannamei larvae.

The potential application of Bdellovibrio-and-like organisms (BALOs) for the biocontrol of bacterial diseases has been widely recognized. However, no marine BALOs have been reported for Vibrio-related infections in penaeid shrimp. In the present study, the bacteriolytic ability of the marine Bacteriovorax strain DA5 against Vibrio alginolyticus zouA was examined by cocultivation and electron microscopy, and optimal lysis was observed at 30-35°C and 20-30‰ salinity along with a high multiplicity of infection. Then, we showed that experimentally infected Litopenaeus vannamei larvae exhibited significantly higher survival with incremental DA5 levels. Finally, variation in the bacterial counts and the bacterial community in larval rearing water was investigated after prophylactic application of DA5. The elimination effect of DA5 on vibrios was visible at early time points, whereas only a few non-dominant bacteria, rather than the predominant populations, were affected through analysis of denaturing gradient gel electrophoresis of the 16S rDNA V3 region. Accordingly, the prophylactic and therapeutic efficacies of DA5 on vibriosis associated with L. vannamei could markedly enhance larval survivability, and these results will facilitate the application of marine Bacteriovorax to control vibriosis in shrimp larviculture.