This study characterizes two temperate bacteriophages, RP2 and RP3, that are integrated into the chromosome of Streptomyces rimosus, an oxytetracycline-producing bacterium. Both phages were identified in lysogenic strains R6-65 and R7. The phages have similar morphology with flexible-tailed, tadpole-shaped particles containing double-stranded DNA approximately 64.7 kb (RP2) and 62.4 kb (RP3) with ~70% G+C content. Both exhibit unusually slow growth kinetics with 6-hour latent periods and 4-hour rise periods. Despite their similarities, RP2 and RP3 are heteroimmune and essentially unrelated, showing completely different restriction maps with only a small region (<430 bp) of sequence homology. Both phages integrate into the host chromosome via site-specific recombination at attachment (att) sites, which were localized to 800 bp and 300 bp fragments respectively. The presence of these prophages did not affect oxytetracycline production or genetic stability. These phages show narrow host range restricted to S. rimosus and represent potentially useful tools for developing genetic vectors and studying prophage roles in Streptomyces biology.

Key findings

• RP2 and RP3 are two heteroimmune, narrow-host-range temperate phages integrated in S. rimosus R6-65 and R7 strains, with genome sizes of 64.7 kb and 62.4 kb respectively and ~70% G+C content
• Both phages display identical, unusually slow growth kinetics with 6-hour latent periods and 4-hour rise periods, the slowest known actinophage replication rates
• RP2 and RP3 are essentially unrelated despite morphological similarities, with completely different restriction maps but containing a conserved homologous region of less than 430 bp near their attachment sites
• Both phages lysogenize via site-specific recombination at att sites localized to 800 bp (RP2) and 300 bp (RP3) restriction fragments
• Prophage presence does not affect oxytetracycline antibiotic production or chromosomal genetic instability in S. rimosus