Characterization and genome analysis of the temperate bacteriophage φSAJS1 from Streptomyces avermitilis

Streptomyces is an important antibiotic-producing bacterium; however, antibiotic production is often negatively affected by bacteriophage contamination. In the present study, the temperate phage φSAJS1 was isolated and characterized from an unsuccessful Streptomyces avermitilis fermentation culture. The complete genome of phage φSAJS1 was sequenced. Phage φSAJS1 belongs to the Siphoviridae family based on its morphology as determined by transmission electron microscopy. Host range analysis indicated that phage φSAJS1 specifically infects various S. avermitilis strains. One-step growth curve assays revealed that Ca²⁺ is required for abundant phage proliferation and that phage φSAJS1 is resistant to high temperatures (70 °C) and alkaline solutions (pH 11). The phage φSAJS1 genome is a circular double-stranded (ds) DNA that does not contain terminal repeats and cohensive ends, thereby suggesting a headful DNA packaging mechanism. The whole phage φSAJS1 genome is 56,451 bp in length with a high GC-content (68.3%) and encodes 76 putative open reading frames. Similarity analysis showed that the majority of the candidate proteins share high similarity (50%-72%) to proteins in the S. griseus subsp. phages YDN12 and TP1604, indicating either a common origin or more recent DNA recombination events throughout the evolution of these three phage lineages.