The damage of outer membrane of Escherichia coli in the presence of TiO2 combined with UV light.

The biological consequences of exposure to TiO2, UV light, and their combined effect were studied on the Escherichia coli (E. coli) cells. The damage of outer membrane was observed for the cells after treatment of TiO2 or UV light. TiO2 alone can break down lipopolysacchride (LPS), the outermost layer of the E. coli cells, but was not able to destroy peptidoglycan underneath. The same phenomenon was observed for E. coli under 500 W UV light treatment alone. However, the outer membrane of E. coli could be removed completely in the presence of both TiO2 and UV light, and the cells became elliptical or round without a mechanically strong network. From the analysis of the concentrations for Ca2+ and Mg2+, a large amount of Ca2+ and Mg2+ were detected in the solution of the treated cells by photo-catalysis, and this was attributed to the damage of LPS dispatches. After TiO2 or UV light treatment, a significant decrease in membrane fluidity of E. coli was found from an increase in fluorescence polarization by a fluorescence probe. The permeability of the treated cells increased to some degree that can be confirmed by quantum dots labeling technique.