ABSTRACTStreptococcus mitisis found in the oral cavity and nasopharynx and forms a significant portion of the human microbiome. In this study,in silicoanalyses indicated the presence of an Rgg regulator and short hydrophobic peptide (Rgg/SHP) cell-to-cell communication system inS. mitis. Although Rgg presented greater similarity to a repressor inStreptococcus pyogenes, autoinducing assays and genetic mutation analysis revealed that inS. mitisRgg acts as an activator. Transcriptome analysis showed that in addition toshp, the system regulates two other downstream genes, comprising a segment of a putative lantibiotic gene cluster that is in a conjugative element locus in different members of the mitis group. Close comparison to a similar lantibiotic gene cluster inStreptococcus pneumoniaeindicated thatS. mitislacked the full set of genes. Despite the potential of SHP to trigger a futile cycle of autoinduction, growth was not significantly affected for therggmutant under normal or antibiotic stress conditions. TheS. mitisSHP was, however, fully functional in promoting cross-species communication and increasingS. pneumoniaesurface polysaccharide production, which in this species is regulated by Rgg/SHP. The activity of SHPs produced by both species was detected in cocultures using aS. mitisreporter strain. In competitive assays, a slight advantage was observed for therggmutants. We conclude that the Rgg/SHP system inS. mitisregulates the expression of its ownshpand activates an Rgg/SHP system inS. pneumoniaethat regulates surface polysaccharide synthesis. Fundamentally, cross-communication of such systems may have a role during multispecies interactions.IMPORTANCEBacteria secrete signal molecules into the environment which are sensed by other cells when the density reaches a certain threshold. In this study, we describe a communication system inStreptococcus mitis, a commensal species from the oral cavity, which we also found in several species and strains of streptococci from the mitis group. Further, we show that this system can promote cross-communication withS. pneumoniae, a closely related major human pathogen. Importantly, we show that this cross-communication can take place during coculture. While the genes regulated inS. mitisare likely part of a futile cycle of activation, the target genes inS. pneumoniaeare potentially involved in virulence. The understanding of such complex communication networks can provide important insights into the dynamics of bacterial communities.
Complete Genome Sequences of Streptococcus mitis Strains Isolated from the Oral Cavity and Urogenital Tract of a Woman and Her Male Sexual Partner
