A Predatory Mechanism Dramatically Increases the Efficiency of Lateral Gene Transfer in Streptococcus Pneumoniae and Related Commensal Species

Bacteria that are competent for natural genetic transformation, such as pneumococci and their commensal relatives Streptococcus mitis and Streptococcus oralis, take up exogenous DNA and incorporate it into their genomes by homologous recombination. Traditionally, it has been assumed that genetic material leaking from dead bacteria constitutes the sole source of external DNA for competent streptococci. Here we describe a mechanism for active acquisition of homologous DNA that dramatically increases the efficiency of gene exchange between and within the streptococcal species mentioned above. This mechanism gives competent streptococci access to a common gene pool that is significantly larger than their own genomes, a property representing a considerable advantage when these bacteria are subjected to external selection pressures, such as vaccination and treatment with antibiotics.