title: Toxicity of ZnO and TiO2to Escherichia coli cells.
abstract: We performed a comprehensive investigation of the toxicity of ZnO and TiO2nanoparticles using Escherichia coli as a model organism. Both materials are wide band gap n-type semiconductors and they can interact with lipopolysaccharide molecules present in the outer membrane of E. coli, as well as produce reactive oxygen species (ROS) under UV illumination. Despite the similarities in their properties, the response of the bacteria to the two nanomaterials was fundamentally different. When the ROS generation is observed, the toxicity of nanomaterial is commonly attributed to oxidative stress and cell membrane damage caused by lipid peroxidation. However, we found that significant toxicity does not necessarily correlate with up-regulation of ROS-related proteins. TiO2exhibited significant antibacterial activity, but the protein expression profile of bacteria exposed to TiO2was different compared to H2O2and the ROS-related proteins were not strongly expressed. On the other hand, ZnO exhibited lower antibacterial activity compared to TiO2, and the bacterial response involved up-regulating ROS-related proteins similar to the bacterial response to the exposure to H2O2. Reasons for the observed differences in toxicity and bacterial response to the two metal oxides are discussed.
authors.affiliation: Dept. of Physics, Univ. of Hong Kong, Pokfulam Road, Hong Kong.
authors.forename: Yu Hang
authors.initials: YH
authors.lastname: Leung
authors.affiliation: School of Energy and Environment, City University of Hong Kong, Kowloon Tong, Hong Kong.
authors.forename: Xiaoying
authors.initials: X
authors.lastname: Xu
authors.affiliation: School of Biological Sciences, Univ. of Hong Kong, Pokfulam Road, Hong Kong.
authors.forename: Angel P Y
authors.initials: AP
authors.lastname: Ma
authors.affiliation: Dept. of Physics, Univ. of Hong Kong, Pokfulam Road, Hong Kong.
authors.forename: Fangzhou
authors.initials: F
authors.lastname: Liu
authors.affiliation: Dept. of Physics, Univ. of Hong Kong, Pokfulam Road, Hong Kong.|Dept. of Physics, South University of Science and Technology of China, Shenzhen, China.
authors.forename: Alan M C
authors.initials: AM
authors.lastname: Ng
authors.affiliation: School of Energy and Environment, City University of Hong Kong, Kowloon Tong, Hong Kong.
authors.forename: Zhiyong
authors.initials: Z
authors.lastname: Shen
authors.affiliation: Pharmaceutical and Life Sciences Division, Waters Corporation, Manchester, UK.
authors.forename: Lee A
authors.initials: LA
authors.lastname: Gethings
authors.affiliation: Dept. of Physics, Univ. of Hong Kong, Pokfulam Road, Hong Kong.|Dept. of Physics, South University of Science and Technology of China, Shenzhen, China.
authors.forename: Mu Yao
authors.initials: MY
authors.lastname: Guo
authors.affiliation: Dept. of Physics, Univ. of Hong Kong, Pokfulam Road, Hong Kong.
authors.forename: Aleksandra B
authors.initials: AB
authors.lastname: Djurišić
authors.affiliation: School of Energy and Environment, City University of Hong Kong, Kowloon Tong, Hong Kong.
authors.forename: Patrick K H
authors.initials: PK
authors.lastname: Lee
authors.affiliation: Dept. of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong.
authors.forename: Hung Kay
authors.initials: HK
authors.lastname: Lee
authors.affiliation: Dept. of Chemistry, Univ. of Hong Kong, Pokfulam Road, Hong Kong.
authors.forename: Wai Kin
authors.initials: WK
authors.lastname: Chan
authors.affiliation: School of Biological Sciences, Univ. of Hong Kong, Pokfulam Road, Hong Kong.
authors.forename: Frederick C C
authors.initials: FC
authors.lastname: Leung
mesh_terms: D000900:Anti-Bacterial Agents / Q000633:toxicity*; D004926:Escherichia coli / Q000187:drug effects* / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D053758:Nanoparticles; D014025:Titanium / Q000633:toxicity*; D015034:Zinc Oxide / Q000633:toxicity*
chemical_list: D000900:Anti-Bacterial Agents; C009495:titanium dioxide; D014025:Titanium; D015034:Zinc Oxide