FIG. 3.

Natural genetic transformation of six S. mutans strains with saturating concentrations of integration plasmid pVA-GTFA as donor DNA (1 μg/ml). Biofilms accumulated on the surfaces of polystyrene microtiter plates for 20 h. Biofilm-grown cells of all strains were able to incorporate foreign DNA more efficiently (10- to 600-fold) than their planktonic (Plank.) counterparts. The transformation frequency is expressed as the percentage of viable cells transformed to erythromycin resistance. The results are expressed as the mean + standard deviation of four independent cultures.