Fate of free DNA and transformation of the oral bacterium Streptococcus gordonii DL1 by plasmid DNA in human saliva

The survival of free DNA in human saliva and its degradation have been studied by using competitive polymerase chain reaction. The free DNA is a 520-bp target sequence from a recombinant plasmid, pVACMC1, after the admixture of the plasmid with freshly-sample human saliva. Results reveal that the plasmid DNA that has been exposed to degradation by human saliva can transform naturally-competent Streptococcus gordonii DL1 to erythromycin resistance. The transformation decreased rapidly with a half-life of 50 seconds.