Virulence of Acute Hepatopancreatic Necrosis Disease PirAB-like Relies on Secreted Proteins Not on Gene Copy Number.

Aims To investigate the virulence of the Vp_PirAB-like genes in Vibrio parahaemolyticus-AHPND causing strain and factors that associate with the virulence level. Methods and Results The virulence of Vp_PirAB-like were examined using a non-virulent strain FP11 of V. parahaemolyticus transformed with a plasmid harboring Vp_PirAB-like genes and then used it to challenge shrimp Litopenaeus vannamei and Marsupenaeus japonicus. Both species experienced 100% mortality 10 days post-infection. Analysis of a mutant strain (E1M), that was originally identified as virulent strain (E1) but lost its virulence to L. vannamei, revealed that it lacked a part of the Vp_PirA-like gene and all of Vp_PirB-like gene. The copy numbers of Vp_PirA-like and Vp_PirB-like genes varied among virulent strains and were not correlated with their virulence. In Western blotting, Vp_PirA-like and Vp_PirB-like proteins were detected in both cell lysate and culture supernatant. The strongest intensity of detecting band in culture supernatant could be observed in the strain that caused the highest mortality. V. parahaemolyticus AHPND-causing strain, unlike the human tdh-positive strain, did not show any enterotoxicity. Conclusion V. parahaemolyticus AHPND-causing strains secret the Vp_PirA-like and Vp_PirB-like proteins during growing phase. The amount of secreted proteins affects the shrimp mortality. Significance and Impact of the Study The secreted proteins of Vp_PirAB-like are key factors of virulence in V. parahaemolyticus AHPND-causing strain, but not gene copy. This article is protected by copyright. All rights reserved.