The role and synergistic effect of the light irradiation and H₂O₂ in photocatalytic inactivation of Escherichia coli

Inactivation of Escherichia coli K-12 was conducted by applying a continuous supplying of commercial H₂O₂ to mimic the H₂O₂ production in a photocatalytic system, and the contribution of H₂O₂ in photocatalytic inactivation was investigated using a modified "partition system" and five E. coli mutants. The concentration of exogenous H₂O₂ required for complete inactivation of bacterial cells was much higher than that produced in-situ in common photocatalytic system, indicating that H₂O₂ alone plays a minor role in photocatalytic inactivation. However, the concentration of exogenously produced H₂O₂ required for effective inactivation of E. coli K-12 was much lower when the light irradiation was applied. To further investigate the possible physiological changes, inactivation of E. coli BW25113 (the parental strain), and its corresponding isogenic single-gene deletion mutants with light pretreatment was compared. The results indicate that light irradiation increases the bacterial intracellular Fe²⁺ level and favors hydroxyl radical (OH) production via the catalytic reaction of Fe²⁺, leading to increase in DNA damage. Moreover, the results indicate that the properties of light source, such as intensity and major emission wavelength, may alter the physiology of bacterial cells and affect the susceptibility to in-situ resultant H₂O₂ in the photocatalytic inactivation processes, leading to significant influence on the photocatalytic inactivation efficiencies of E. coli K-12.