Evidence of the horizontal transfer of pVA1-type plasmid from AHPND-causing V. campbellii to non-AHPND V. owensii

Abstract

Acute hepatopancreatic necrosis disease (AHPND) is a bacterial disease of marine shrimp that has caused severe economic losses to aquaculture producers in affected areas. AHPND was originally found to be caused by virulent strains of Vibrio parahaemolyticus (VpAHPND). These pathogenic strains carry pirABvp genes, which produce a binary toxin and are located on pVA1-type plasmid. Subsequently, it was found that AHPND can also be caused by pathogenic strains of other Vibrio species including: V. harveyi-like, V. campbellii, V. punensis, and V. owensii, all of which harbor a pVA1-type plasmid. Here we hypothesize that the pVA1-type plasmid can be transferred horizontally among Vibrio species. We carried out laboratory studies confirming the horizontal transfer of pVA1-type plasmid from AHPND-causing V. campbellii strain 20130629003S01 (VcAHPND-3S01) to a non-AHPND V. owensii strain 20160513VC2W (Vo-VC2W). ANI analysis revealed that strain Vo-VC2W is closely related to the V. owensii strain XSBZ03 isolated from corals in the South China Sea. However, the pirABvp genes on the transferred plasmid were unstable and lost from the pVA1-type plasmid of Vo-VC2W after 2 sub-culture passages. The sequences of the pVA1-type plasmid in AHPND-Vc3S01 and ΔpirABvpVo-VC2W were highly homologous (99.9% identical), indicating that this plasmid acquired by the V. owensii was from the AHPND-V. campbellii strain. In addition, complete genome sequence of the ΔpirABvpVo-VC2W showed that it contains 2 chromosomes and 3 plasmids; its detailed genomic characteristics will provide relevant information for better understanding of a V. owensii isolate that harbors transferred pVA1-type plasmid.