Transfer of plasmids pBR322 and pBR325 in wastewater from laboratory strains of Escherichia coli to bacteria indigenous to the waste disposal system.

Laboratory strains of Escherichia coli containing plasmid pBR325 (or pBR322) were coincubated with a mobilizer strain of E. coli (containing the conjugative plasmid R100-1) and a recipient strain of bacteria. Bacterial strains isolated from raw wastewater or a plasmid-free E. coli laboratory strain served as recipients. Transfer of the pBR plasmid into the recipient strain occurred during a 25-h coincubation in either L broth or sterilized wastewater; transfer frequencies were several orders of magnitude lower in wastewater. After the coincubation, recipients exhibited both plasmid-encoded phenotypic characteristics and an altered plasmid profile, as shown by agarose gel electrophoresis of purified plasmid DNA.