Characterization and genome analysis of a novel bacteriophage vB_SpuP_Spp16 that infects Salmonella enterica serovar pullorum.

A novel virulent bacteriophage vB_SpuP_Spp16 (hereafter designated Spp16) that infects Salmonella enterica serovar pullorum was isolated. Transmission electron microscopy showed that Spp16 possessed an isometric polyhedral head (60 nm in diameter) and a short tail (10 nm in length) belonging to the family Podoviridae. Its complete genome was determined to be 41,832 bp, with a 39.46% GC content by next-generation sequencing. The genome contains 53 proposed open reading frames that are involved in DNA replication and modification, transcriptional regulation, phage structural and packaging proteins and bacterial lysis. No transfer RNA genes were identified. The termini of genome were determined using our previously proposed termini identification method, which suggests that this phage has redundant termini with 421 bp direct terminal repeats. BLASTn analysis revealed the highest sequence similarity with Yersinia phage phi80-18, with a genome coverage of 33% and highest sequence identity of 69%. The phylogenetic analysis indicated that Spp16 forms a distinct branch of the subfamily Autographivirinae. Comparative genomics analysis showed that the phage Spp16 should be regarded as a new subcluster within the GAP227-like cluster in the Autographivirinae subfamily. The phage Spp16 has an obligate lytic life cycle demonstrated by experimental data and genomic analysis. These results suggest that Spp16 may be a proper candidate to control diseases caused by Salmonella enterica serovar pullorum.