Horizontal gene transfer of thepirABgenes responsible for Acute Hepatopancreatic Necrosis Disease (AHPND) turns a non-Vibriostrain 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°) of pirAB from V. parahaemolyticus to Algoriphagus sp. strain NBP at 30°C and 40°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.

Toxin-linked mobile genetic elements in major enteric bacterial pathogens

“…Further, cross species HGT of toxin genes has been demonstrated by Muthukrishnan et al (2019) through co-culture experiments of pirAB positive V. parahaemolyticus isolates and pirAB negative Algoriphagus sp. Strain.…”

First report and pathogenicity of Vibrio campbellii (VCAHPND) isolated in South Korea

“…According to reports on the PirA/B toxin genes present in pVA1, V. parahaemolyticus strains lacking PirA/B fail to cause AHPND; however, the strains transformed with plasmids containing PirA/B have been found to show clinical signs of AHPND and cause 100% mortality in shrimp larvae (Muthukrishnan, Defoirdt, Ina‐Salwany, et al., 2019; Muthukrishnan, Defoirdt, Shariff, et al., 2019; Tinwongger et al., 2016). Additionally, pVA1 can be transferred among similar clusters and is capable of self‐transfer using the pndA PSK gene system, which is a mobilizing gene associated with conjugative transfer (Lee et al., 2015).…”

“…The isolated HJ‐2023 strain was confirmed to be V. campbellii via gene sequence identification, but the same result was not obtained in the bacterial identification based on the biochemical characteristics determined using the API tests, as the information on V. campbellii was not registered in the bacterial identification reading software; therefore, it was likely confirmed as a similar Vibrio species. Because of this diversity in biochemical characteristics, when bacteria are isolated from diseased white‐leg shrimp using TCBS medium, approximately 84.3% of them form green colonies (Muthukrishnan, Defoirdt, Ina‐Salwany, et al., 2019; Muthukrishnan, Defoirdt, Shariff, et al., 2019). V. campbellii also forms green colonies because it lacks a sucrose hydrolase gene, making it difficult to distinguish it from V. parahaemolyticus (Dong, Bi, Wang, et al., 2017; Dong, Wang, Xie, et al., 2017; Dong, Wang, Zou, et al., 2017).…”

“…However, according to the results of the present study, although VC non‐AHPND itself causes mortality in shrimp, V. campbellii is conferred this ability by the pVA1 plasmid and appears to potentially cause stronger pathogenicity in shrimp. AHPND‐causing V. harveyi is more virulent than the V. harveyi involved in non‐AHPND (Muthukrishnan, Defoirdt, Ina‐Salwany, et al., 2019; Muthukrishnan, Defoirdt, Shariff, et al., 2019). The present study indicates that when devising measures to prevent the spread of AHPND, quarantine focusing on the V. parahaemolyticus strain, which is believed to be a unique strain of AHPND, is not a clear solution.…”

A Review of the Functional Annotations of Important Genes in the AHPND-Causing pVA1 Plasmid

“…Another report confirmed that pVA1 pirAB vp genes could be transferred from an AHPND-causing V. parahaemolyticus to a non- Vibrio and non-pathogenic Algoriphagus sp. [ 25 ]. These developments suggest that pVA1-related plasmids could be transmitted between different species, which would make it more difficult to control AHPND.…”