Long-term evolution of Streptococcus mitis and Streptococcus pneumoniae leads to higher genetic diversity within rather than between human populations.

A recent study examined the genetic diversity and evolution of Streptococcus mitis and Streptococcus pneumoniae, two types of bacteria commonly found in the human oronasopharynx. The study found that there is higher genetic diversity within populations of S. mitis compared to S. pneumoniae. This difference is attributed to the larger historical population size of S. mitis, which has maintained genetic variation over many generations, while S. pneumoniae has expanded from a smaller ancestral population and has been subjected to adaptive selection. Both species showed limited differentiation among populations, suggesting that large population size is a common feature of the human microbiome. [Extracted from the article]