BlpC-mediated selfish program leads to rapid loss of Streptococcus pneumoniae clonal diversity during infection.

Successful colonization of a host requires bacterial adaptation through genetic and population changes that are incompletely defined. Using chromosomal barcoding and high-throughput sequencing, we investigate the population dynamics of Streptococcus pneumoniae during infant mouse colonization. Within 1 day post inoculation, diversity was reduced >35-fold with expansion of a single clonal lineage. This loss of diversity was not due to immune factors, microbiota, or exclusive genetic drift. Rather, bacteriocins induced by the BlpC-quorum sensing pheromone resulted in predation of kin cells. In this intra-strain competition, the subpopulation reaching a quorum likely eliminates others that have yet to activate the blp locus. Additionally, this reduced diversity restricts the number of unique clones that establish colonization during transmission between hosts. Genetic variation in the blp locus was also associated with altered transmissibility in a human population, further underscoring the importance of BlpC in clonal selection and its role as a selfish element. [Display omitted] • Streptococcus pneumoniae show loss of clonal diversity early during colonization • Bactericidal program induced by quorum sensing pheromone BlpC reduces diversity • BlpC signaling tightens bottlenecks and drives loss of diversity during transmission Aggarwal et al. report evidence of extensive loss of diversity due to intra-strain competition during nasopharyngeal colonization by Streptococcus pneumoniae. Activation of a quorum sensing-induced bactericidal program led to predation of kin cells during within-host colonization as well as tightening of population bottlenecks during transmission between hosts. [ABSTRACT FROM AUTHOR]