EFFECT OF LIGHT ON THIOBACILLI

Abstract

The aim was to study the effect of visible and ultra-violet light on some members of the genus Thiobacillus. This genus is one more example of an aerobic organism which undergoes what appears to be the widespread phenomenon of light inhibition. Light inhibition of thiobacilli has been observed before and these other observations are presented. In the present study the effect of both visible and U-V light on three species was considered viz. T.thiooxidans, T.thioparus and T.ferrooxidans, the latter species being studied more thoroughly with respect to different intensities and wavelengths of light and the shielding effect of bacterial numbers and ferric iron. The photoreactivation of T.ferrooxidans cells after irradiation by U-V light was also examined, Using unfiltered, visible light, there was an inhibitory effect on all three of the thiobacilli irrespective of the energy source being used. When selected wavelengths were studied it was seen that the blue end of the visible spectrum was most inhibitory. A relationship between ferric iron concentration and protection from visible light» was shown and the beneficial protective effect of particulate suspensions was demonstrated. afforded by ferric iron and cell numbers was assessed. Photoreactivation of U-V irradiated cells by exposure to visible light showed that this phenomenon occurred using wavelengths of visible light which, by themselves, were inhibitory. Some practical implication of these findings are offered.