The opportunistic marine pathogen Vibrio parahaemolyticus becomes virulent by acquiring a plasmid that expresses a deadly toxin

Abstract

Acute hepatopancreatic necrosis disease (AHPND) is a severe, newly emergent penaeid shrimp disease caused by Vibrio parahaemolyticus that has already led to tremendous losses in the cultured shrimp industry. Until now, its disease-causing mechanism has remained unclear. Here we show that an AHPND-causing strain of V. parahaemolyticus contains a 70-kbp plasmid (pVA1) with a postsegregational killing system, and that the ability to cause disease is abolished by the natural absence or experimental deletion of the plasmid-encoded homologs of the Photorhabdus insect-related (Pir) toxins PirA and PirB. We determined the crystal structure of the V. parahaemolyticus PirA and PirB (PirAvp and PirBvp) proteins and found that the overall structural topology of PirAvp/PirBvp is very similar to that of the Bacillus Cry insecticidal toxin-like proteins, despite the low sequence identity (<10%). This structural similarity suggests that the putative PirABvp heterodimer might emulate the functional domains of the Cry protein, and in particular its pore-forming activity. The gene organization of pVA1 further suggested that pirABvp may be lost or acquired by horizontal gene transfer via transposition or homologous recombination.

Acute Hepatopancreatic Necrosis Disease-Causing Vibrio parahaemolyticus Strains Maintain an Antibacterial Type VI Secretion System with Versatile Effector Repertoires

“…Strain FIM-S1708ϩ was excluded from this analysis because the genome se-quence of this isolate did not contain complete pirA vp and pirB vp genes. The pirA vp and pirB vp genes are flanked by two inverted copies of a transposase, suggesting that the toxic genes are likely acquired by AHPND strains from an unknown foreign source (8,12). PirA vp /PirB vp are homologues of the insecticidal toxins PirA/PirB of the Photorhabdus and Xenorhabdus genera (8).…”

“…The pirA vp and pirB vp genes are flanked by two inverted copies of a transposase, suggesting that the toxic genes are likely acquired by AHPND strains from an unknown foreign source (8,12). PirA vp /PirB vp are homologues of the insecticidal toxins PirA/PirB of the Photorhabdus and Xenorhabdus genera (8). Although the mechanism underlying the toxicity of PirA vp /PirB vp is still unknown, the binary toxins share high structural similarities with the Bacillus pore-forming Cry insecticidal toxin (8).…”

“…PirA vp /PirB vp are homologues of the insecticidal toxins PirA/PirB of the Photorhabdus and Xenorhabdus genera (8). Although the mechanism underlying the toxicity of PirA vp /PirB vp is still unknown, the binary toxins share high structural similarities with the Bacillus pore-forming Cry insecticidal toxin (8).…”

Necrosis aguda del hepatopáncreas: una revisión de la enfermedad en Penaeus vannamei

“…No así con la secuencia que codifica para la toxina Pir A, la cual presenta altas diferencias con respecto a otras secuenciadas previamente, descritas para P. luminescens (Han et al, 2015d;Lee et al, 2015).…”

Structural classification of insecticidal proteins – Towards an in silico characterisation of novel toxins

“…Table 1 shows the toxin classes, colour-coded by sequence homology groups. As can be seen, the 3-domain Cry toxins represent the largest structural family (and also encompass the PirA/B toxin, recently shown to be equivalent to a 3-domain toxin with a dissociated domain III (Lee et al, 2015)). There is also a large group of toxins that is rich in beta-sheets with general structural similarity to aerolysin.…”