Bacterial SOS response as a potential driver of antibiotic resistance gene transfer in wastewater

Wastewater treatment plants have been highlighted numerous times as hotspots for anthropogenic environmental pollution with antibiotic resistance genes and resistant bacteria. However, demonstrating horizontal gene transfer events in these environments has been challenging. The role of SOS response, that has been shown to promote horizontal gene transfer through other mechanisms such as transduction, is often overlooked. In the present study, we evaluated whether SOS response could be induced in influent and effluent samples from wastewater treatment plants and compared them to reference points and samples upstream and downstream of the wastewater treatment plants. Our results demonstrate that influent samples from three Swedish wastewater treatment plants could induce SOS response to a higher level than mitomycin C at 0.5 ng/ml in a reporter E. coli strain. While bacteriophage induction was not directly measured, SOS response induced at such concentrations of mitomycin C has been previously demonstrated to induce latent bacteriophages in E. coli. Bacteriophages can mobilize antibiotic resistance genes and facilitate genetic exchange between bacteria, serving as vehicles for horizontal gene transfer of antibiotic resistance genes in wastewater environments. These results suggest that SOS response could play an important role for the spread of antibiotic resistance genes in wastewater. Consequently, establishing pre-treatment strategies for wastewater may be beneficial to prevent genetic exchange between environmental bacteria and human and animal pathogens.