Genetic exchange between Treponema denticola and Streptococcus gordonii in biofilms

Some gram-positive oral bacteria such as Streptococcus gordonii are naturally transformable. We investigated the possibility of genetic exchange among oral bacteria using an erythromycin-resistant (Erm(r)) shuttle plasmid, pKMR4PE, as an indicator. S. gordonii Challis cells were co-cultivated with purified pKMR4PE or with Trepomena denticola harboring pKMR4PE either in broth or in artificial biofilms. Transformation of S. gordonii occurred both in broth and in biofilms with pKMR4PE or T. denticola harboring pKMR4PE as donor sources. These results provide direct experimental evidence that gene transfer can occur from T. denticola to S. gordonii.