Return of Streptococcus faecalis DNA cloned in Escherichia coli to its original host via transformation of Streptococcus sanguis followed by conjugative mobilization.

Cloning vectors were introduced into Streptococcus faecalis by conjugation. A conjugative plasmid (pVA797) and cloning vector pVA838 recombined in Streptococcus sanguis at homologous sequences, forming a cointegrate. The pVA797::pVA838 cointegrate transferred to S. faecalis by conjugation. Recombination between homologous sequences resolved the cointegrate in the S. faecalis transconjugants, and pVA797 and pVA838 segregated because of incompatibility. S. faecalis strains that received pVA838 by this mechanism contained plasmids indistinguishable from authentic pVA838 from Escherichia coli. Other plasmids, including pVA736, were introduced into S. faecalis by this method. This approach should facilitate the introduction of cloned DNA into S. faecalis.