The Effect of UV-A and Various Visible Light Wavelengths Radiations on Ex- pression Level of Escherichia coli Oxidative Enzymes in Seawater

Background: Light and photosensitizers affectthe survival of bacteria in natural environments. Also light and photosensitizers are used for disinfection of materials such as blood, blood products, and water. Objectives: The present study was aimed toinvestigate the effect of different wavelengths of visible light and UV-A on the synthesis of some oxidative stress enzymes of Escherichia coli (E. coli) in seawater. Materials and Methods: Seawater were filtered by using Whatmann No:1 filter paper, followed by sterilization in the autoclave. The E. coli W3110 strain was grown at 37 oC, centrifuged, and transferred in seawater, then methylene blue was added to the seawater samples, with the exception of control samples. The seawater samples were incubated with white, blue, green, red, and UV-A light sources. Cell extracts were prepared by sonication, and then catalase, superoxide dismutase (SOD), glutathion peroxidase(GP),and glucose-6phosphate dehydrogenase(G-6-PD) activities were measured. Results: It was found that in all studied wavelengths with or without Methylene Blue (MB), the level of all studied enzymes decreased remarkably when compared to dark controls. It was observed that the synthesis level of SOD, glutathione peroxidase GP, and glucose 6 phosphate dehydrogenase G-6-PD in E. coli decreased significantly in red light with respect to white, blue, and green light in seawater, to which methylene blue was added. In E. coli the decrease was 13% of G-6-PD expression, 10% of GP expression, and 17% of SOD expression in red light with MB after 16-hour incubation in seawater; however, these enzymes decreased to 45%, 84%,and 71% in white light, 33%, 47%, and 54% in blue light, 53%, 53%,and 64% in green light at the same incubation hours, respectively. Also, the enzyme acitivity in red light without MB did not show a significant difference when compared to other light sources. Conclusions: It was shown in the present study that red light among visible light sources has a crucial effect in decreasing the oxidative stress enzymes in seawater containing MB.