Deciphering Pneumococcal Encryption: The Role of Peptides in Inter-Strain and Inter-Species Communication

About This Grant

Project Summary Cell-cell communication (CCC) systems in Streptococcus pneumoniae (Spn) are key determinants of colonization, a prerequisite to invasive disease in this major human pathogen. While most studies have focused on CCC within a single strain, the role of intra- and inter-species interactions in Spn colonization and virulence remains poorly understood. We have identified the Rgg144/SHP144 peptide-regulated signaling system in Spn and characterized its components, regulation, and function in colonization and pathogenesis. Notably, this CCC system is not only conserved across Spn strains but is also present in 20% of its co-colonizing commensal, Streptococcus mitis (Sm). Our comparative genomic studies reveal that both species encode diverse alleles of the Rgg144 receptor and the SHP144 peptide, with some SHP144 alleles being identical between Spn and Sm. Furthermore, specific Rgg144-SHP144 allele pairs co-occur across the pangenome, with certain residues co- varying, suggesting the existence of pherotypes—wherein SHP144 from one pherotype activates its cognate receptor but not others. Our preliminary data confirm the functional existence of these pherotypes through experiments testing diverse SHP144 alleles against a single Rgg144 receptor. This study will test the hypothesis that Spn and Sm strains interact within and across species via Rgg144/SHP144 signaling, thereby modulating colonization and expanding our understanding of microbial communication in the upper respiratory tract. The research plan includes an in-depth analysis of Rgg144-SHP144 to define the specificity of SHP144 binding to diverse Rgg144 alleles, identify the residues conferring specificity to this interaction, examine how non-cognate SHP144 peptides influence signaling, and quantify signaling in a murine model of Spn disease (Aim 1). We find that key components of this CCC regulon differ across stains and species. Thus, the role of regulon and how it influences strain fitness and growth will be studied in vitro and in vivo, with a focus on biofilm growth and architecture (Aim 2). To expand the clinical relevance, we will leverage a large collection of human upper respiratory tract samples to establish the functional significance of the Rgg144- SHP144 locus and its downstream effectors in naturally occurring multi-strain and multi-species colonization (Aim 3). By elucidating mechanisms of intra and interspecies Spn communication, this work will provide key insights into microbial interactions in the upper respiratory tract and identify potential targets for novel therapeutics.