Microbial Musings – Winter 2022

and assessing peptides found in cell- free supernatant using mass spectrometry. They find a 16 amino peptide that shares similarity with other Mitis group streptococci, although there is significant sequence diversity amongst the different species. This CSP is released from early to mid- log phase as judged by the activation of expression of the comX gene that is switched on by the quorum- sensing pathway being activated. They show that synthetic CSP from their strain- induced competence, but this was not observed using a distinct CSP from a related strain, demonstrating high specificity of this sensing mechanism. To see which other genes are switched on they isolated RNA from matched cultures with added synthetic CSP or a DMSO control and used RNAseq to determine the differentially expressed genes. They find many of the genes they would have predicted to be involved in competence development, as expected, but also other genes involved in biofilm production and virulence. However, they directly assess biofilm formation in response to different concentrations of CSP and see no direct impact on this phenotype, suggesting there is additional regulatory control of biofilm formation, and they propose the differential regulation of some of the genes involved in this pathway by CSP might have become relevant during growth in the natural polymicrobial oral cavity.