Electrotransformation and natural transformation of Streptococcus pneumoniae: requirement of DNA processing for recombination.

Electrotransformation has been used as a tool to introduce genes carried on replicative vectors in hundreds of bacterial species. In this study, the technique was used to try to obtain recombination of markers in the chromosome of the naturally transformable bacterium Streptococcus pneumoniae. Recombination was not observed even using naturally competent cultures. Both chromosomal and cloned DNA, denatured or native, were without effect. These results suggest that it is not sufficient to introduce DNA into the cell to obtain recombinants in this bacterium. The integration of markers into the chromosome in naturally competent cells must require DNA processing during entry. Electrotransformation of replicating plasmids is recA-independent but can be facilitated by a recA-dependent process. This facilitation required the induction of the natural competence machinery, probably involving partial homologous pairing.