Novel Virulent Bacteriophage ΦSG005, Which Infects Streptococcus gordonii, Forms a Distinct Clade among Streptococcus Viruses.

Bacteriophages are viruses that specifically infect bacteria and are classified as either virulent phages or temperate phages. Despite virulent phages being promising antimicrobial agents due to their bactericidal effects, the implementation of phage therapy depends on the availability of virulent phages against target bacteria. Notably, virulent phages of Streptococcus gordonii, which resides in the oral cavity and is an opportunistic pathogen that can cause periodontitis and endocarditis have previously never been found. We thus attempted to isolate virulent phages against S. gordonii. In the present study, we report for the first time a virulent bacteriophage against S. gordonii, ΦSG005, discovered from drainage water. ΦSG005 is composed of a short, non-contractile tail and a long head, revealing Podoviridae characteristics via electron microscopic analysis. In turbidity reduction assays, ΦSG005 showed efficient bactericidal effects on S. gordonii. Whole-genome sequencing showed that the virus has a DNA genome of 16,127 bp with 21 coding sequences. We identified no prophage-related elements such as integrase in the ΦSG005 genome, demonstrating that the virus is a virulent phage. Phylogenetic analysis indicated that ΦSG005 forms a distinct clade among the streptococcus viruses and is positioned next to streptococcus virus C1. Molecular characterization revealed the presence of an anti-CRISPR (Acr) IIA5-like protein in the ΦSG005 genome. These findings facilitate our understanding of streptococcus viruses and advance the development of phage therapy against S. gordonii infection.

Distinct Biological Potential of Streptococcus gordonii and Streptococcus sanguinis Revealed by Comparative Genome Analysis.

Streptococcus gordonii and Streptococcus sanguinis are pioneer colonizers of dental plaque and important agents of bacterial infective endocarditis (IE). To gain a greater understanding of these two closely related species, we performed comparative analyses on 14 new S. gordonii and 5 S. sanguinis strains using various bioinformatics approaches. We revealed S. gordonii and S. sanguinis harbor open pan-genomes and share generally high sequence homology and number of core genes including virulence genes. However, we observed subtle differences in genomic islands and prophages between the species. Comparative pathogenomics analysis identified S. sanguinis strains have genes encoding IgA proteases, mitogenic factor deoxyribonucleases, nickel/cobalt uptake and cobalamin biosynthesis. On the contrary, genomic islands of S. gordonii strains contain additional copies of comCDE quorum-sensing system components involved in genetic competence. Two distinct polysaccharide locus architectures were identified, one of which was exclusively present in S. gordonii strains. The first evidence of genes encoding the CylA and CylB system by the α-haemolytic S. gordonii is presented. This study provides new insights into the genetic distinctions between S. gordonii and S. sanguinis, which yields understanding of tooth surfaces colonization and contributions to dental plaque formation, as well as their potential roles in the pathogenesis of IE.

Characterization of Streptococcus gordonii prophage PH15: complete genome sequence and functional analysis of phage-encoded integrase and endolysin.

Streptococcus gordonii OMZ1039, isolated from supragingival dental plaque, was found to harbour a prophage, PH15, whose excision could be induced by mitomycin treatment. Phage PH15 belongs to the Siphoviridae. The complete genome sequence of PH15 was determined. The genome was 39 136 bp in size and contained 61 ORFs. The genome of PH15 was most similar in the structural module to the temperate bacteriophages MM1 and phiNIH1.1 from Streptococcus pneumoniae and Streptococcus pyogenes, respectively. In strain OMZ1039, PH15 was found to reside as a prophage in the cysteinyl-tRNA gene. A plasmid, harbouring the attP site and the integrase gene downstream of a constitutive promoter, was capable of site-specific integration into the genomes of different oral streptococcal species. The phage endolysin was purified after expression in Escherichia coli and found to inhibit growth of all S. gordonii strains tested and several different streptococcal species, including the pathogens Streptococcus mutans, S. pyogenes and Streptococcus agalactiae.