Genome sequencing reveals that Streptococcus pneumoniae possesses a large and diverse repertoire of antimicrobial toxins

Streptococcus pneumoniae ('pneumococcus') is a leading cause of morbidity and mortality worldwide and a frequent coloniser of the nasopharynx. Competition among bacterial members of the nasopharynx is believed to be mediated by bacteriocins: antimicrobial toxins produced by bacteria to inhibit growth of other bacteria. Bacteriocins are also promising candidates for novel antimicrobials. Here, 14 newly-discovered bacteriocin gene clusters were identified among >6,200 pneumococcal genomes. The molecular epidemiology of the bacteriocin clusters was investigated using a large global and historical pneumococcal dataset. The analyses revealed extraordinary bacteriocin diversity among pneumococci and the majority of bacteriocin clusters were also found in other streptococcal species. Genomic hotspots for the integration of bacteriocin genes were discovered. Experimentally, bacteriocin genes were transcriptionally active when the pneumococcus was under stress and when two strains were competing in broth co-culture. These findings fundamentally expand our understanding of bacteriocins relative to intraspecies and interspecies nasopharyngeal competition.