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

Hao-Ching Wang,Ramya Kumar,Han-Ching Wang,Shin-Jen Lin,Arpita Mohapatra

doi:10.3390/microorganisms8070996

Abstract

Acute hepatopancreatic necrosis disease (AHPND) is a lethal shrimp disease. The pathogenic agent of this disease is a special Vibrio parahaemolyticus strain that contains a pVA1 plasmid. The protein products of two toxin genes in pVA1, pirAvp and pirBvp, targeted the shrimp’s hepatopancreatic cells and were identified as the major virulence factors. However, in addition to pirAvp and pirBvp, pVA1 also contains about ~90 other open-reading frames (ORFs), which may encode functional proteins. NCBI BLASTp annotations of the functional roles of 40 pVA1 genes reveal transposases, conjugation factors, and antirestriction proteins that are involved in horizontal gene transfer, plasmid transmission, and maintenance, as well as components of type II and III secretion systems that may facilitate the toxic effects of pVA1-containing Vibrio spp. There is also evidence of a post-segregational killing (PSK) system that would ensure that only pVA1 plasmid-containing bacteria could survive after segregation. Here, in this review, we assess the functional importance of these pVA1 genes and consider those which might be worthy of further study.

Highlights

Acute hepatopancreatic necrosis disease (AHPND) is a bacterial disease that causes severe damage in shrimp farming [1]
By acquiring a unique plasmid, pVA1, that encodes the binary pore-forming toxins PirAvp and PirBvp, V. parahaemolyticus has become a lethal pathogen to penaeid shrimps [4,5,6,7,8,9,10]
Whole-genome sequencing of 40 V. parahaemolyticus isolated from shrimp hepatopancreas and aquaculture water in Malaysia indicated that pirABvp genes are prone to deletion [51]. These results demonstrate the importance of this DNA transposon in the transfer, deletion, and mutation of the pirABvp-containing gene cluster

Summary

Introduction

Acute hepatopancreatic necrosis disease (AHPND) is a bacterial disease that causes severe damage in shrimp farming [1]. In the course of the disease, apart from the PirABvp toxins, there is very little that is known of the functional roles of other genes/proteins from the pVA1 plasmid, as well as those from the V. parahaemolyticus bacterium itself. To address these issues, advanced techniques, such as generation sequencing, structural biology, and system biology have been applied [5,13,14]. Studies that look beyond the PirABvp toxins can provide valuable insights into AHPND, to date, there are still only a handful of reports that relate to other gene products of the pVA1 plasmid

The AHPND-Causing Plasmid pVA1

Conclusion