Freeze-thaw-induced lateral transfer of non-conjugative plasmids by in situ transformation in Escherichia coli in natural waters and food extracts

Freeze-thaw treatment of condensed suspensions of mixed Escherichia coli strains in natural waters and food extracts caused in situ lateral transfer of non-conjugative plasmids. This phenomenon also occurred in distilled water and LB broth, and after 1-2 months of preservation at -20 degrees C. The sensitivity of lateral transfer towards DNase activity suggested the involvement of in situ transformation. There were no clear correlations between transformation frequency and the chemical characteristics (Ca(2+) , Mg(2+), and pH) of the samples. These results suggest the possibility that freeze-thaw-induced lateral gene transfer between bacterial cells occurs in natural and human environments.