Characterization of a T7-like lytic bacteriophage (ɸSG-JL2) of Salmonella enterica serovar Gallinarum biovar Gallinarum

Abstract

ɸSG-JL2 is a newly discovered lytic bacteriophage infecting Salmonella enterica serovar Gallinarum biovar Gallinarum (S. Gallinarum), but is non-lytic to a rough vaccine strain of S. Gallinarum(SG-9R), Salmonella Enteritidis, Salmonella Typhimurium, and Salmonella enterica serovar Gallinarum biovar Pullorum (S. Pullorum). The ɸSG-JL2 genome is 38,815 bp in length (GC content of 50.9% and 230 bp length direct terminal repeats) and 55 putative genes may be transcribed from the same strand. Functions were assigned to 30 genes based on the high amino acid similarity with known proteins. Most of the expected proteins except tail fiber (31.9%) and overall organization of genomes were similar to yersiniophage ɸYeO3-12. ɸSG-JL2 could be classified as a new T7-like virus and represents the first S. Gallinarum phage genome to be sequenced. On the basis of intraspecific ratios of nonsynonymous to synonymous nucleotide changes (Pi[a]/Pi[s]), gene 2 encoding host RNA polymerase inhibitor displayed Darwinian positive selection. Pre-treatment of chickens with ɸSG-JL2 before intratracheal challenge with wild-type S. Gallinarum protected most birds from fowl typhoid. Therefore, ɸSG-JL2 may be useful for differentiation of S. Gallinarum from other Salmonella serotypes, prophylactic application to fowl typhoid control, and understanding of vertical evolution of T7-like viruses.