Conjugative Transfer of the pVA1-Type Plasmid Carrying the Genes Results in the Formation of New AHPND-Causing .

Acute hepatopancreatic necrosis disease (AHPND) has caused sharp declines in aquaculture industries of whiteleg shrimp in Asia and the Americas since 2010. , and have been proved to cause AHPND. However, the mechanisms underlying the burgeoning number of species that cause AHPND is not known. All of AHPND-causing bacteria () harbor a highly homologous plasmid (designated as pVA1-type) carrying toxin genes. In this study, we demonstrate conclusively that the pVA1-type plasmid can be transferred from to non-pathogenic bacteria. We constructed a pVPGX1- plasmid (a pVA1-type plasmid) by adding a chloramphenicol resistance gene as a marker in a donor AHPND-causing 20130629002S01 (2S01). Horizontal transfer of this plasmid was successfully performed from the AHPND-2S01 to a non-pathogenic strain of at the transfer efficiency of 2.6×10 transconjugant/recipient, and DNase I treatment did not eliminate the transfer. The recipient acquired the pVA1-type plasmid and was shown to produce RNA and proteins. Challenge studies using the transconjugant caused 100% mortality in exposed groups of . The challenged shrimp, infected with the transconjugant bacteria, showed typical gross signs and histological lesions of AHPND. These results demonstrated the conjugative transfer of an AHPND pVA1-type plasmid. It provides timely information for explaining the increased species of AHPND-causing bacteria and will be useful in the development of management strategies leading to the prevention and control of AHPND.