AUTHOR=Mendonca Michelle L. , Szamosi Jake C. , Lacroix Anne-Marie , Fontes Michelle E. , Bowdish Dawn M. , Surette Michael G. 

TITLE=The sil Locus in Streptococcus Anginosus Group: Interspecies Competition and a Hotspot of Genetic Diversity

JOURNAL=Frontiers in Microbiology

VOLUME=7

YEAR=2017

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2016.02156

DOI=10.3389/fmicb.2016.02156

ISSN=1664-302X

ABSTRACT=<p>The <italic>Streptococcus</italic> Invasion Locus (<italic>Sil</italic>) was first described in <italic>Streptococcus pyogenes</italic> and <italic>Streptococcus pneumoniae</italic>, where it has been implicated in virulence. The two-component peptide signaling system consists of the SilA response regulator and SilB histidine kinase along with the SilCR signaling peptide and SilD/E export/processing proteins. The presence of an associated bacteriocin region suggests this system may play a role in competitive interactions with other microbes. Comparative analysis of 42 <italic>Streptococcus</italic> Anginosus/Milleri Group (SAG) genomes reveals this to be a hot spot for genomic variability. A cluster of bacteriocin/immunity genes is found adjacent to the <italic>sil</italic> system in most SAG isolates (typically 6–10 per strain). In addition, there were two distinct SilCR peptides identified in this group, denoted here as SilCR<sub>SAG-A</sub> and SilCR<sub>SAG-B</sub>, with corresponding alleles in <italic>silB</italic>. Our analysis of the 42 <italic>sil</italic> loci showed that SilCR<sub>SAG-A</sub> is only found in <italic>Streptococcus intermedius</italic> while all three species can carry SilCR<sub>SAG-B</sub>. In <italic>S. intermedius</italic> B196, a putative SilA operator is located upstream of bacteriocin gene clusters, implicating the <italic>sil</italic> system in regulation of microbe–microbe interactions at mucosal surfaces where the group resides. We demonstrate that <italic>S. intermedius</italic> B196 responds to its cognate SilCR<sub>SAG-A</sub>, and, less effectively, to SilCR<sub>SAG-B</sub> released by other Anginosus group members, to produce putative bacteriocins and inhibit the growth of a sensitive strain of <italic>S. constellatus</italic>.</p>