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Abstract
The solar water disinfection (SODIS) method relies on UV-A irradiation from natural sunlight for bactericidal treatment of drinking water. This study investigated the indirect effects of UV-A irradiation on Escherichia coli growth, death and gene expression. It has been previously shown that reactive oxygen species (ROS) induced by UV-A irradiation 760 affect cell death rates. Three E.coli K12 strains – χ, UM2, JW3914 – were exposed to UV-A to investigate a potential correlation between UV-A-induced catalase expression and cell mortality. Turbidity and colony forming unit assays were performed to investigate cell growth and cell death respectively. As expected, an E.coli strain with katG/katE double knock-out showed a greater increase of death rate compared to the wild-type E.coli exposed to UV-A irradiation. However, differential catalase genotypes did not affect growth rate in our experimental model. A reporter system using a plasmid construct containing the katG promoter linked to detectable luxCDABE genes of Photorhabdus luminescens was used to examine the induction of katG expression in E.coli RFM443 by UV-A irradiation. katG expression was significantly up-regulated when E.coli incubated in water was exposed to UV-A irradiation; however, this increase was abrogated within Luria-Bertani media.