Genomic characterization and comparison of seven Myoviridae bacteriophage infecting Bacillus thuringiensis

Bacillus thuringiensis Kurstaki, a bacterium that is a source of biopesticides and a safe simulant for pathogenic Bacillus species, was used to isolate seven unique bacteriophages. The phage genomes were sequenced and ranged in size from 158,100 to 163,019 bp encoding 290-299 genes, and the GC content of ~38% was similar to that of the host bacterium. All phages had terminal repeats 2-3 kb long. Three of the phages encoded tRNAs and three contained a self-splicing intron in the DNA polymerase gene. They were categorized as a single cluster (>60% nucleotide conservation) containing three subclusters (>80% nucleotide conservation), supported by genomic synteny and phylogenetic analysis. Considering the published genomes of phages that infect the genus Bacillus and noting the ability of many of the Bacillus cereus group phages to infect multiple species, a clustering system based on gene content is proposed.