Phage 3396 from a Streptococcus dysgalactiae subsp. equisimilis pathovar may have its origins in streptococcus pyogenes.

Streptococcus dysgalactiae subsp. equisimilis strains (group G streptococcus [GGS]) are largely defined as commensal organisms, which are closely related to the well-defined human pathogen, the group A streptococcus (GAS). While lateral gene transfers are emerging as a common theme in these species, little is known about the mechanisms and role of these transfers and their effect on the population structure of streptococci in nature. It is now becoming evident that bacteriophages are major contributors to the genotypic diversity of GAS and, consequently, are pivotal to the GAS strain structure. Furthermore, bacteriophages are strongly associated with altering the pathogenic potential of GAS. In contrast, little is know about phages from GGS and their role in the population dynamics of GGS. In this study we report the first complete genome sequence of a GGS phage, Phi3396. Exhibiting high homology to the GAS phage Phi315.1, the chimeric nature of Phi3396 is unraveled to reveal evidence of extensive ongoing genetic diversity and dissemination of streptococcal phages in nature. Furthermore, we expand on our recent findings to identify inducible Phi3396 homologues in GAS from a region of endemicity for GAS and GGS infection. Together, these findings provide new insights into not only the population structure of GGS but also the overall population structure of the streptococcal genus and the emergence of pathogenic variants.