title: Dual Roles of Capsular Extracellular Polymeric Substances in Photocatalytic Inactivation of Escherichia coli: Comparison of E. coli BW25113 and Isogenic Mutants.
abstract: The dual roles of capsular extracellular polymeric substances (EPS) in the photocatalytic inactivation of bacteria were demonstrated in a TiO2-UVA system, by comparing wild-type Escherichia coli strain BW25113 and isogenic mutants with upregulated and downregulated production of capsular EPS. In a partition system in which direct contact between bacterial cells and TiO2 particles was inhibited, an increase in the amount of EPS was associated with increased bacterial resistance to photocatalytic inactivation. In contrast, when bacterial cells were in direct contact with TiO2 particles, an increase in the amount of capsular EPS decreased cell viability during photocatalytic treatment. Taken together, these results suggest that although capsular EPS can protect bacterial cells by consuming photogenerated reactive species, it also facilitates photocatalytic inactivation of bacteria by promoting the adhesion of TiO2 particles to the cell surface. Fluorescence microscopy and scanning electron microscopy analyses further confirmed that high capsular EPS density led to more TiO2 particles attaching to cells and forming bacterium-TiO2 aggregates. Calculations of interaction energy, represented by extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) potential, suggested that the presence of capsular EPS enhances the attachment of TiO2 particles to bacterial cells via acid-base interactions. Consideration of these mechanisms is critical for understanding bacterium-nanoparticle interactions and the photocatalytic inactivation of bacteria.
authors.affiliation: School of Life Sciences, The Chinese University of Hong Kong, Shatin, NT, Hong Kong SAR, China.
authors.forename: Guocheng
authors.initials: G
authors.lastname: Huang
authors.affiliation: School of Life Sciences, The Chinese University of Hong Kong, Shatin, NT, Hong Kong SAR, China.
authors.forename: Dehua
authors.initials: D
authors.lastname: Xia
authors.affiliation: State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China antc99@gig.ac.cn pkwong@cuhk.edu.hk.
authors.forename: Taicheng
authors.initials: T
authors.lastname: An
authors.affiliation: School of Life Sciences, The Chinese University of Hong Kong, Shatin, NT, Hong Kong SAR, China.
authors.forename: Tsz Wai
authors.initials: TW
authors.lastname: Ng
authors.affiliation: School of Life Sciences, The Chinese University of Hong Kong, Shatin, NT, Hong Kong SAR, China.
authors.forename: Ho Yin
authors.initials: HY
authors.lastname: Yip
authors.affiliation: State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China.
authors.forename: Guiying
authors.initials: G
authors.lastname: Li
authors.affiliation: Centre for Clean Environment and Energy, Griffith School of Environment, Griffith University, Gold Coast, Queensland, Australia.
authors.forename: Huijun
authors.initials: H
authors.lastname: Zhao
authors.affiliation: School of Life Sciences, The Chinese University of Hong Kong, Shatin, NT, Hong Kong SAR, China antc99@gig.ac.cn pkwong@cuhk.edu.hk.
authors.forename: Po Keung
authors.initials: PK
authors.lastname: Wong
mesh_terms: D016667:Bacterial Capsules / Q000187:drug effects* / Q000528:radiation effects*; D058491:Bacterial Load; D004926:Escherichia coli / Q000166:cytology / Q000187:drug effects* / Q000502:physiology / Q000528:radiation effects*; D050296:Microbial Viability / Q000187:drug effects* / Q000528:radiation effects*; D008853:Microscopy; D010083:Oxidants, Photochemical / Q000633:toxicity*; D014025:Titanium / Q000633:toxicity; D014466:Ultraviolet Rays
chemical_list: D010083:Oxidants, Photochemical; C009495:titanium dioxide; D014025:Titanium