Horizontal gene transfer of the pirAB genes responsible for Acute Hepatopancreatic Necrosis Disease (AHPND) turns a non-Vibrio strain into an AHPND-positive pathogen

Abstract

In the past decade, shrimp farms, particularly those established in Asia, Mexico and South America suffered from the outbreak of an emergent penaeid shrimp disease known as Acute Hepatopancreatic Necrosis Disease (AHNPD). The PirA and PirB toxins produced by plasmid pVA1 in Vibrio parahaemolyticus were reported to cause the AHPND pathology. More recent research demonstrated that V. parahaemolyticus is not the only species that can cause AHPND, as other Vibrio species were also found to contain PirAB-containing plasmid. The present study assessed the Horizontal Gene Transfer (HGT) of AHPND that transforms genes (pirA and pirB) from AHPND positive V. parahaemolyticus to non-AHPND and non-vibrio species identified as Algoriphagus sp. strain NBP. The HGT of pirA and pirB genes from the AHPND positive V. parahaemolyticus to Algoriphagus sp. strain NBP was found to occur at different temperatures. The conjugation efficiency rate (n{degrees}) of pirAB from V. parahaemolyticus to Algoriphagus sp. strain NBP at 30{degrees}C and 40{degrees}C showed 80-91% efficiency. Shrimp challenged with the pirA and pirB positive Algoriphagus sp. strain NBP also demonstrated typical pathognomonic AHPND lesions during the histopathologic examination. Author summaryAHPND is a significant threat to the shrimp industry leading to high losses. The results demonstrated that the conjugative transfer of the pirA and pirB positive V. parahaemolyticus (donor strain) to a non-Vibrio and non-pathogenic bacterium (recipient strain), successfully transformed the non-pathogenic bacterium into a disease-causing strain with a disease-causing capability similar to the donor strain. Initially, V. parahaemolyticus that express the PirA and PirB toxins which encoded by a conjugative plasmid cause sloughing and degeneration of shrimp hepatopancreatic.