Photocatalysis is a promising water purification method due to its potential of using solar energy directly and achieving both microbial disinfection and chemical detoxification.There are some proposed mechanisms of photocatalytic inactivation of Escherichia coli by ultraviolet(UVA)-titanium dioxide(TiO2)system,however,there are still considerable debates on them.This project investigated the photocatalytic inactivation efficiency of E.coli BW25113(parental strain)and its isogenic mutants,and hence to study the inactivation mechanism underlying from genetic approach.E.coli mutants related to fatty acid biosynthesis(fabR-)and degradation(fadR-)were found to have significant difference in the inactivation efficiency,comparing to the parental strain.The inactivation kinetic constants of the parental strain and selected mutants had been determined using disinfection model and shown good correlations with the ratio of unsaturated fatty acid to saturated fatty acid.Results of Live Dead BacLight Bacterial Viability Kit analysis and scavenger study indicated that the cell membrane is the primary target of reactive species generated by photocatalysis.These results were further confirmed by the measurement of malondialdehyde(MDA),the most widely used biomarker for lipid peroxidation,during the photocatalytic inactivation of bacterial cells.These results highlight the overall importance of cell membrane in photocatalytic inactivation of bacteria.The results of this project can provide new insight on the mechanism of photocatalytic inactivation,and help to modify present water disinfection using photocatalysis.