Two T2SS homologous genes of pVA plasmid affect biological characteristics and PirAB expression and secretion of Vibrio parahaemolyticus

Abstract:

[Background] Vibrio parahaemolyticus is one of the pathogens causing acute hepatopancreatic necrosis disease (AHPND) in cultured shrimp. PirAB, encoded by pirA and pirB located on the plasmid pVA, acts as the virulence factor of AHPND. However, the secretion pathway of PirABremains unclear. [Objective] To explore the effect of two T2SS homologous genes epsG2 and epsE2 of pVA on biological characteristics and PirAB expression and secretion of Vibrio parahaemolyticus. [Methods] The bioinformatics analysis revealed two type II secretion system (T2SS) homologous genes epsG2 and epsE2 on the pVA plasmid in V. parahaemolyticus VP220218. The mutants ΔepsG2 and ΔepsE2 were constructed by in-frame deletion. The growth, biofilm formation, swimming ability, and extracellular protease activity were compared between VP220218 and mutants. RT-qPCR and Western blotting were performed to compare the expression and secretion of PirAB between VP220218 and mutants.[Results] epsG2 and epsE2 suppressed the extracellular protease activity (P<0.001) and the growth during the logarithmic stage (P<0.05). In addition, epsG2 promoted the swimming (P<0.05) and inhibited the biofilm formation of VP220218 at the plateau stage (P<0.05); epsE2 restrained the swimming ability and promoted the biofilm formation of VP220218 at the middle and late logarithmic stage (P<0.05). The results of RT-qPCR showed that epsE2 had no effect on the expression of pirA or pirB; epsG2 inhibited the expression of pirA and pirB at the early and middle logarithmic stage, while it promoted the expression of pirA and pirBat the late logarithmic stage and plateau stage. The results of Western blotting showed that epsE2 promoted the synthesis and secretion of PirAB while epsG2 had no significant effect on the synthesis or secretion of PirAB. [Conclusion] The results indicated that epsG2 and epsE2 were involved in the physiological activities of V. parahaemolyticus VP220218. Moreover, epsE2 affected the synthesis and secretion of PirAB. The findings provided a reference for understanding the synthetic and secretory pathways of PirAB in AHPND-causing bacteria.

Key words:acute hepatopancreatic necrosis disease in shrimp;Vibrio parahaemolyticus;type II secretory system;epsG2;epsE2