Abstract
Acute hepatopancreatic necrosis disease (AHPND) has caused sharp declines in aquaculture industries of whiteleg shrimp Penaeus vannamei in Asia and the Americas since 2010. Vibrio parahaemolyticus, V. campbellii, V. owensii, and V. punensis have been proved to cause AHPND. However, the mechanisms underlying the burgeoning number of Vibrio species that cause AHPND is not known. All of AHPND-causing Vibrio bacteria (VAHPND) harbor a highly homologous plasmid (designated as pVA1-type) carrying pirABvp toxin genes. In this study, we demonstrate conclusively that the pVA1-type plasmid can be transferred from VAHPND to non-pathogenic bacteria. We constructed a pVPGX1-Cmr plasmid (a pVA1-type plasmid) by adding a chloramphenicol resistance gene as a marker in a donor AHPND-causing V. parahaemolyticus 20130629002S01 (Vp2S01). Horizontal transfer of this plasmid was successfully performed from the AHPND-Vp2S01 to a non-pathogenic strain of V. campbellii at the transfer efficiency of 2.6×10−8 transconjugant/recipient, and DNase I treatment did not eliminate the transfer. The recipient V. campbellii acquired the pVA1-type plasmid and was shown to produce pirABvp RNA and proteins. Challenge studies using the transconjugant caused 100% mortality in exposed groups of P. vannamei. 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 Vibrio bacteria and will be useful in the development of management strategies leading to the prevention and control of AHPND.
Highlights
Acute hepatopancreatic necrosis disease (AHPND, known as early mortality syndrome, EMS) affects marine shrimp Penaeus vannamei and P. monodon
Horizontal gene transfer is a driver for diversification of pathogenic bacteria via mobile genetic elements (MGEs) including plasmids, transposons, insertion sequences (ISs), FIGURE 2 | Expression of pirABvp genes in Vibrio campbellii and V. parahaemolyticus. (A) RT-PCR detection of pirAvp and pirBvp expression
(B) Cumulative mortality of shrimp infected with V. campbellii LMB29 (VcLMB29)-pVPGX1, shrimp were exposed to Virbio bacteria through immersion infection
Summary
Acute hepatopancreatic necrosis disease (AHPND, known as early mortality syndrome, EMS) affects marine shrimp Penaeus vannamei and P. monodon. Recent studies found that AHPND could be caused by strains of other Vibrio species, such as V. harveyi-like, V. campbellii, V. owensii, and V. punensis (Kondo et al, 2015; Liu et al, 2015, 2018; Dong et al, 2017b; Han et al, 2017; Restrepo et al, 2018). Strains of these Vibrio species, collectively abbreviated as VAHPND, that contain the pVA1-type plasmids as well as secreting both PirAvp and PirBvp proteins, can cause AHPND
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