Toxicological assessment of TiO2 nanoparticles by recombinant Escherichia coli bacteria

Rapid and efficient methods to assess nanoparticle toxicity are desired in current research. Here we showed that Escherichia coli labeled by green fluorescent protein can be a good model bacterium for assessing acute toxicity of TiO2 (about 50% inhibition ratios after 135 min exposure). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed that TiO2 nanoparticles (NPs) can influence certain protein expression in the recombinant bacterium, and the obvious effects in repressed expression and elevated expression were observed in 30/40, 10/20 mu g mL(-1) treated cells, respectively. However, the GFP expression (27 kD) was not influenced by introduced TiO2 NPs. The change of the fluorescence intensity may be caused by the damage in folding and chromophore formation of the GFP post-translational modification due to generated reactive oxygen species. Furthermore, TiO2 NPs at higher concentrations decreased their toxicity because of aggregation. 20 mu g mL(-1) humic acid (HA) introduced to the medium can decrease the fluorescent inhibition owing to the barrier of steric hindrance it provides between NPs and cells.