Unveiling the photoelectrocatalytic inactivation mechanism of Escherichia coli: Convincing evidence from responses of parent and anti-oxidation single gene knockout mutants.
This study investigated photoelectrocatalytic (PEC) inactivation mechanism of bacteria using parental Escherichia coli (E. coli) BW25113 and its isogenic mutants deficient in catalase HPI (katG(-), JW3914-1) and Mn-SOD (sodA(-), JW3879-1). BW25113 in the mid-log phase was less susceptible to PEC inactivation than those in early-log and stationary phases, consistent with the peak activities of catalase and superoxide dismutase (SOD) at mid-log phase (30.6 and 13.0 Unit/ml/OD600). For different strains all in mid-log phase, PEC inactivation efficiency followed the order katG(-) > sodA(-) > BW25113, with the duration of 60, 60 and 90 min for complete inactivation of ∼2 × 10(7) CFU mL(-1) bacteria, respectively. Correspondingly, catalase and SOD levels of BW25113 were also higher than the mutants by 5.9 and 11.7 Unit/mL/OD600, respectively. Reactive oxygen species (ROSs) concentrations in PEC systems revealed that the inactivation performance coincided with H2O2 levels, rather than OH. Moreover, pre-incubation with H2O2 elevated catalase activities and PEC inactivation resistance of BW25113 were positively correlated. The above results indicated that H2O2 was the dominant PEC generated bactericide, and anti-oxidative enzymes especially catalase contributed greatly to the bacterial PEC resistance capacity. Further tests revealed that PEC treatment raised the intracellular ROSs concentration by more than 3 times, due to the permeated H2O2 and its intracellular derivative, OH. However, oxidative stress response of E. coli, such as increased catalase or SOD were not observed, perhaps because the ROSs overwhelmed the bacterial protective capacity. The accumulated ROSs subsequently caused oxidative damages to E. coli cells, including membrane damage, K(+) leakage, and protein oxidation. Compared with BW25113, the mutants experienced damages earlier and at higher levels, confirming the essential roles of catalase and SOD in the bacterial PEC resistance.
The State Key Laboratory of Organic Geochemistry and Guangdong Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China; University of Chinese Academy of Sciences, Beijing, China.
Hongwei
H
Sun
The State Key Laboratory of Organic Geochemistry and Guangdong Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China.
Guiying
G
Li
The State Key Laboratory of Organic Geochemistry and Guangdong Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China. Electronic address: antc99@gig.ac.cn.
Taicheng
T
An
Centre for Clean Environment and Energy, Griffith University, Gold Coast Campus, QLD, Australia.
Huijun
H
Zhao
School of Life Sciences, The Chinese University of Hong Kong, Hong Kong Special Administrative Region. Electronic address: pkwong@cuhk.edu.hk.
Po Keung
PK
Wong
D002374:Catalase / Q000235:genetics / Q000378:metabolism; D002384:Catalysis; D004203:Disinfection / Q000379:methods*; D004560:Electricity; D004926:Escherichia coli / Q000201:enzymology / Q000378:metabolism / Q000528:radiation effects*; D055786:Gene Knockout Techniques; D006861:Hydrogen Peroxide / Q000378:metabolism*; D008027:Light; D009154:Mutation; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000528:radiation effects; D055668:Photochemical Processes; D017382:Reactive Oxygen Species / Q000378:metabolism; D013482:Superoxide Dismutase / Q000235:genetics / Q000378:metabolism; D014871:Water Microbiology
D017382:Reactive Oxygen Species; D006861:Hydrogen Peroxide; D002374:Catalase; D013482:Superoxide Dismutase
Catalase; Hydrogen peroxide; Oxidative stress; Photocatalytic disinfection; Superoxide dismutase