Use of Biosensors to Study the Mechanisms of UV-Based Water Disinfection

Bioreporters and biosensors can report not only external stimuli but also the internal conditions in the cell they are embedded in. Here, we used bioreporters to explore the effect of UV sources with different spectra on bacteria. UV irradiation is a common physical method for water disinfection and for the inactivation of pathogenic bacteria, viruses, and protozoa. Two types of UV lamps are used, i.e., Low-Pressure (LP) and Medium-Pressure (MP) lamps, where pressure relates to mercury vapor pressure.

MP lamps have polychromatic irradiation spectra, while LP lamps have an almost monochromatic spectrum, with 99% of the irradiation at ~254nm. In inactivation studies, MP lams have been shown to be more effective in preventing bacteria recovery, but the mechanisms underlying this phenomenon have not been fully understood.

Bioreporters offer a way to see the bacterial “point-of-view” of the irradiation. We studied the bacterial response to the two UV sources using E. coli strains containing different promoters upstream to the lux operon and exposing these bacteria to sub-lethal LP and MP irradiation. Following promotor activation, we found that MP irradiation results in the formation of Super Oxide (O₂•^-) inside the cells, probably due to the interaction of the MP lamp spectra's higher wavelength with specific amino acids. These radicals have also been found to play a major role in the disinfection process. These results could explain the disinfecting effects of UVA/B treatments that were previously described and could help in the design of better systems.