Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2016 Oct 12:6:35243.
doi: 10.1038/srep35243.

Toxicity of ZnO and TiO2 to Escherichia coli cells

Yu Hang Leung  1 , Xiaoying Xu  2 , Angel P Y Ma  3 , Fangzhou Liu  1 , Alan M C Ng  1   4 , Zhiyong Shen  2 , Lee A Gethings  5 , Mu Yao Guo  1   4 , Aleksandra B Djurišić  1 , Patrick K H Lee  2 , Hung Kay Lee  6 , Wai Kin Chan  7 , Frederick C C Leung  3
Affiliations

Toxicity of ZnO and TiO2 to Escherichia coli cells

Yu Hang Leung et al. Sci Rep. .

Abstract

We performed a comprehensive investigation of the toxicity of ZnO and TiO2 nanoparticles 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. TiO2 exhibited significant antibacterial activity, but the protein expression profile of bacteria exposed to TiO2 was different compared to H2O2 and 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.

PubMed Disclaimer

Conflict of interest statement

The authors declare no competing financial interests.

Figures

Figure 1
Figure 1. Survival percentages of E. coli bacteria after UV illumination for 20 min.
For different starting bacterial and nanoparticle concentrations (a) ZnO nanoparticles (b) TiO2 nanoparticles.
Figure 2
Figure 2. Representative SEM images of E. coli bacterial cells after exposure to ZnO nanoparticles with different concentrations (0.01, 0.1 and 1.0 mg/ml).
Left-most column indicates the initial bacterial concentrations (106, 107 and 108 CFU/ml).
Figure 3
Figure 3. Representative SEM images of E. coli bacterial cells after exposure to TiO2 nanoparticles with different concentrations (0.01, 0.1 and 1.0 mg/ml).
Left-most column indicates the initial bacterial concentrations (106, 107, and 108 CFU/ml).
Figure 4
Figure 4
Electron spin resonance (ESR) spectra for ZnO and TiO2 nanoparticles with different concentrations (a) with DMPO spin trap, without E. coli (b) DEPMPO spin trap, without E. coli. (c) DMPO spin trap, with E. coli (d) DEPMPO spin trap, with E. coli. In all cases, E. coli concentration was 106 CFU/ml. The spectra of H2O2 solutions are also shown for comparison.
Figure 5
Figure 5. Expression of ROS-related proteins under different conditions.
“∞” represents the expression of proteins in the treated cells but no protein was detected in the control. “−” represents no protein was detected in both the treated and control cells. “*”represents genes that were statistically significant (FDR ≤1%, peptide count ≥3, fold-change ≥2). Expression ratios were calculated with the protein abundance measured in the control as the denominator.
Figure 6
Figure 6. Expression of ROS-related proteins without UV illumination.
(A) Thermal stress treated cells. (B) ZnO (0.1 mg/ml) treated cells. “*” represents genes that were statistically significant (FDR ≤1%, peptide count ≥3, fold-change ≥2). Expression ratios were calculated with the protein abundance measured in the control as the denominator.
Figure 7
Figure 7
ATR-FTIR spectra of E. coli exposed to ZnO and TiO2 (a) entire spectral range; (b,c,d) relevant spectral ranges where significant changes are observed.
See this image and copyright information in PMC

References

    1. Huh A. J. & Kwon Y. J. “Nanoantibiotics”: a new paradigm for treating infectious diseases using nanomaterials in the antibiotics resistant era. J. Controlled Release 156, 128–145 (2011). - PubMed
    1. von Moos N. & Slaveykova V. I. Oxidative stress induced by inorganic nanoparticles in bacteria and aquatic microalgae–state of the art and knowledge gaps. Nanotoxicology 8, 605–630 (2014). - PubMed
    1. Foster H. A., Ditta I. B., Varghese S. & Steele A. Photocatalytic disinfection using titanium dioxide: spectrum and mechanism of antimicrobial activity. Appl. Microbiol. Biotechnol. 90, 1847–1868 (2011). - PMC - PubMed
    1. Aruguete D. M. & Hochella M. F. Bacteria–nanoparticle interactions and their environmental implications. Environ. Chem. 7, 3–9 (2010).
    1. Guadagnini R. et al.. Toxicity screenings of nanomaterials: challenges due to interference with assay processes and components of classic in vitro tests. Nanotoxicology 9, 13–24 (2015). - PubMed

Publication types

MeSH terms