Characterization of Diverse Prophages of the Oral Commensal Streptococcus Gordonii

Objectives: Streptococci are the most abundant bacteria in most sub-habitats in the human oral microbiome and are major contributors to the development of dental biofilms. Among the streptococci, Streptococcus gordonii (hereafter, Sg) are pioneer colonizers of exposed oral surfaces, and have been found to both inhibit and facilitate colonization by potential pathogens, including, for example, S. mutans and Porphyromonas gingivalis. However, a broad aspect of Sg ecology remains poorly understood - how its colonization dynamics and interactions are shaped by infections by phage predators and symbionts. Previous work by others identified an active prophage in a strain of Sg, and showed that its endolysin inhibited growth of multiple species of streptococci, and we hypothesize that the diversity and functional impact of Sg prophages are greater than currently recognized.
Methods: Here we use bioinformatic approaches to systematically characterize all publically available Sg genomes for the presence of prophages.
Results: In this work, we show that putative prophages are present in genomes of numerous Sg isolates, and that these represent at least 19 new candidate species in 12 new candidate genera of phages. Characterization of these prophages reveals genes that may potentially contribute to Sg resistance to stress, as well numerous genes encoding proteins with as yet unknown functions.
Conclusions: These findings establish a foundation for systematic laboratory-based studies of the impacts of prophages on Sg colonization dynamics and interactions with other microbes in the oral microbiome.