Pathogenicity of a Vibrio owensii strain isolated from Fenneropenaeus chinensis carrying pirAB genes and causing AHPND

Abstract

An emergent shrimp disease, acute hepatopancreatic necrosis disease (AHPND), has been causing great economic losses to the shrimp farming industry. The original causing agent of AHPND was regarded as Vibrio parahaemolyticus, with a plasmid named pVA1 carrying two Photorhabdus insect-related (Pir) toxin genes pirA and pirB. In the present study, a Vibrio owensii strain named FcYS03 was isolated from the Chinese shrimp Fenneropenaeus chinensis, which caused a high mortality in shrimp with typical AHPND signs. This strain carried the binary toxin genes pirAB and could cause AHPND both in Fenneropenaeus chinensis and Penaeus vannamei (previously named Litopenaeus vannamei). The pathogenicity of FcYS03 to P. vannamei exhibited apparent temperature and salinity dependence. Through genome sequence analysis among FcYS03 and AHPND-causing V. parahaemolyticus strain 3HP, we found that a segmental rearrangement phenomenon existed in the plasmid of FcYS03. The toxin genes pirAB happened to be located at the rearranged segment, and two transposases for transposon Tn903 were distributed at the two ends of the rearranged segment, which indicated that transposon Tn903 might be related to the transfer of the toxin genes among the bacteria. The study will provide valuable information for the understanding and prevention of AHPND in shrimp aquaculture.