Synergistic effects of biofloc and the probiotic Pseudoalteromonas piscicida 1Ub on suppression of virulence gene expression in Vibrio parahaemolyticus and immunity enhancement in Pacific white shrimp.

The pathogenicity of Vibrio parahaemolyticus is regulated by quorum sensing (QS) mechanisms, which are controlled by QS regulators such as OpaR and AphA. This necessitates strategies to control its population and reduce virulence while boosting shrimp immunity. It is currently known that Vibrio parahaemolyticus can cause acute hepatopancrease necrotic disease (AHPND) in white shrimp, supported by the QS mechanism. This study assessed the expression of V. parahaemolyticus virulence genes and the immune response of Pacific white shrimp raised in a biofloc system supplemented with the probiotic Pseudoalteromonas piscicida 1Ub. The shrimp, with an average weight of 1.31 ± 0.001 g, were reared for 21 days at a density of 1 shrimp per liter and subjected to different treatments, including biofloc, probiotics, and their combination, followed by V. parahaemolyticus challenge. Gene expression analysis indicated that these treatments effectively reduced V. parahaemolyticus virulence and enhanced shrimp immunity compared to the challenge control (P < 0.05), with a significant reduction in the bacterial count. Additionally, survival rates, growth performance, and immune responses, including total hemocyte count, respiratory burst, phenol oxidase activity, and phagocytosis, were notably higher in treated groups compared to the challenge control (P < 0.05). This study suggests that biofloc combined with P. piscicida 1Ub may modestly reduce V. parahaemolyticus QS and virulence gene expression at an early stage and may help enhance shrimp immunity and survival. Further studies with extended time points are recommended to verify these effects.