Bamboo powder protects gnotobiotically-grown brine shrimp against AHPND-causing Vibrio parahaemolyticus strains by cessation of PirAB(VP) toxin secretion

Acute hepatopancreatic necrosis disease (AHPND), caused by virulent Vibrio parahaemolyticus strains, is causing havoc in the shrimp industry. However, the culture conditions markedly influence the phenotypic status of V. parahaemolyticus. For instance, under low shaking conditions, the free-living planktonic virulent form of AHPND-causing V. parahaemolyticus switches into a non-virulent biofilm phenotype. Hence, strategies that could stimulate phenotype switching can be a novel way to control AHPND in shrimp. In this study, we evaluated the role of bamboo powder, a natural biofilm carrier, on the phenotypic switch in AHPND-causing and non-AHPND V. parahaemolyticus strains under both in vitro and in vivo conditions. The results showed that bamboo powder addition (50?100 mg/l) significantly enhanced the survival of brine shrimp larvae upon challenge with AHPND M0904 and RY strains. Furthermore, addition of bamboo powder also has profound effects on the phenotypic responses of AHPND-causing V. parahaemolyticus strains. The V. parahaemolyticus AHPND strains (M0904 and RY) grown with bamboo powder developed cellular aggregates or floccules in the culture medium and switch in the pattern of protein production and secrete alkaline phosphatase PhoX instead of PirAVP and PirBVP toxins. Based on the overall results, it can be suggested that bamboo powder induces phenotype switching, which might contribute in part to the protection of the brine shrimp larvae against AHPND-causing V. parahaemolyticus.