Genome-wide characterization of Vibrio phage φpp2 with unique arrangements of the mob-like genes.

BACKGROUND

Vibrio parahaemolyticus is associated with gastroenteritis, wound infections, and septicemia in human and animals. Phages can control the population of the pathogen. So far, the only one reported genome among giant vibriophages is KVP40: 244,835 bp with 26% coding regions that have T4 homologs. Putative homing endonucleases (HE) were found in Vibrio phage KVP40 bearing one segD and Vibrio cholerae phage ICP1 carrying one mobC/E and one segG.

RESULTS

A newly isolated Vibrio phage φpp2, which was specific to the hosts of V. parahaemolyticus and V. alginolyticus, featured a long nonenveloped head of ~90 × 50 nm and tail of ~110 nm. The phage can survive at 50°C for more than one hour. The genome of the phage φpp2 was sequenced to be 246,421 bp, which is 1587 bp larger than KVP40. 383 protein-encoding genes (PEGs) and 30 tRNAs were found in the phage φpp2. Between the genomes of φpp2 and KVP40, 254 genes including 29 PEGs for viral structure were of high similarity, whereas 17 PEGs of KVP40 and 21 PEGs of φpp2 were unmatched. In both genomes, the capsid and tail genes have been identified, as well as the extensive representation of the DNA replication, recombination, and repair enzymes. In addition to the three giant indels of 1098, 1143 and 3330 nt, ϕpp2 possessed unique proteins involved in potassium channel, gp2 (DNA end protector), tRNA nucleotidyltransferase, and mob-type HEs, which were not reported in KVP40. The φpp2 PEG274, with strong promoters and translational initiation, was identified to be a mobE type, flanked by NrdA and NrdB/C homologs. Coincidently, several pairs of HE-flanking homologs with empty center were found in the phages of Vibrio phages φpp2 and KVP40, as well as in Aeromonas phages (Aeh1 and Ae65), and cyanophage P-SSM2.

CONCLUSIONS

Vibrio phage φpp2 was characterized by morphology, growth, and genomics with three giant indels and different types of HEs. The gene analysis on the required elements for transcription and translation suggested that the φpp2 PEG274 was an active mobE gene. The phage was signified to be a new species of T4-related, differing from KVP40.