Effect of Intrastrain Variation in the Amount of Capsular Polysaccharide on Genetic Transformation of Streptococcus pneumoniae: Implications for Virulence Studies of Encapsulated Strains

The degrees of competence of opaque and transparent colony variants of Streptococcus pneumoniae were compared. The transparent variants were transformed at 9- to 670-fold-higher rates than the opaque variants, independent of the DNA incorporated, due to decreased expression of capsular polysaccharide. Genetic transformation, therefore, tends to select for a less-encapsulated subpopulation.