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Abstract
Solar water disinfection (SODIS) is an inexpensive method whereby bottled water is exposed to sunlight for five hours to inactivate and destroy pathogens, thus rendering it safe for drinking. This is especially practical in developing countries where one third of the population has no access to safe drinking water. The mechanism of SODIS has been proposed to involve two synergetic factors, ultraviolet-A radiation which generates reactive oxygen species (ROS), and increases in water temperature. Previously, the proposed UV-A mechanism was studied by comparing survival rates of Escherichia coli strains with mutations of catalase and peroxidase genes. The Δ katE Δ katG double mutant strain suffered a greater loss of viable cells upon exposure to UV-A radiation than a Δ katG mutant, suggesting the importance of the katE gene. In this study, we examined whether a katE – complemented mutant still lacking katG would have a better survival rate compared to the double mutant. Bottles of water containing various E. coli mutants were subjected to 90 minutes of UV-A treatment, with vigorous shaking at 15 minute intervals. Survival rates were determined by bacterial enumeration using pour plate technique. Surprisingly, our katE -complemented mutant had the lowest survival rate compared to the other strains, suggesting that katE alone does not protect cells from UV-A irradiation and that overexpression of catalase may be detrimental.