Characterization of a new plasmid-like prophage in a pandemic Vibrio parahaemolyticus O3:K6 strain.

Vibrio parahaemolyticus is a common food-borne pathogen that is normally associated with seafood. In 1996, a pandemic O3:K6 strain abruptly appeared and caused the first pandemic of this pathogen to spread throughout many Asian countries, America, Europe, and Africa. The role of temperate bacteriophages in the evolution of this pathogen is of great interest. In this work, a new temperate phage, VP882, from a pandemic O3:K6 strain of V. parahaemolyticus was purified and characterized after mitomycin C induction. VP882 was a Myoviridae bacteriophage with a polyhedral head and a long rigid tail with a sheath-like structure. It infected and lysed high proportions of V. parahaemolyticus, Vibrio vulnificus, and Vibrio cholerae strains. The genome of phage VP882 was sequenced and was 38,197 bp long, and 71 putative open reading frames were identified, of which 27 were putative functional phage or bacterial genes. VP882 had a linear plasmid-like genome with a putative protelomerase gene and cohesive ends. The genome does not integrate into the host chromosome but was maintained as a plasmid in the lysogen. Analysis of the reaction sites of the protelomerases in different plasmid-like phages revealed that VP882 and PhiHAP-1 were highly similar, while N15, PhiKO2, and PY54 made up another closely related group. The presence of DNA adenine methylase and quorum-sensing transcriptional regulators in VP882 may play a specific role in this phage or regulate physiological or virulence-associated traits of the hosts. These genes may also be remnants from the bacterial chromosome following transduction.