Effect of ZnO and TiO2 nanoparticles preilluminated with UVA and UVB light on Escherichia coli and Bacillus subtilis

Toxicity of TiO2 nanoparticles to Escherichia coli: effects of particle size, crystal phase and water chemistry

Controversial and inconsistent results on the eco-toxicity of TiO2 nanoparticles (NPs) are commonly found in recorded studies and more experimental works are therefore warranted to elucidate the nanotoxicity and its underlying precise mechanisms. Toxicities of five types of TiO2 NPs with different particle sizes (10∼50 nm) and crystal phases were investigated using Escherichia coli as a test organism. The effect of water chemistry on the nanotoxicity was also examined. The antibacterial effects of TiO2 NPs as revealed by dose-effect experiments decreased with increasing particle size and rutile content of the TiO2 NPs. More bacteria could survive at higher solution pH (5.0-10.0) and ionic strength (50-200 mg L(-1) NaCl) as affected by the anatase TiO2 NPs. The TiO2 NPs with anatase crystal structure and smaller particle size produced higher content of intracellular reactive oxygen species and malondialdehyde, in line with their greater antibacterial effect. Transmission electron microscopic observations showed the concentration buildup of the anatase TiO2 NPs especially those with smaller particle sizes on the cell surfaces, leading to membrane damage and internalization. These research results will shed new light on the understanding of ecological effects of TiO2 NPs.

Conducting a battery of bioassays for gold nanoparticles to derive guideline value for the protection of aquatic ecosystems

Gold nanoparticles (Au-NPs) are used in many applications, including the manufacture of products like cosmetics, paints, and electrochemical immunosensors, and in the detection, diagnosis, and treatment of tumors. However, there are no legal or recommended guidelines for protecting aquatic ecosystems from Au-NPs. In this study, we conducted a battery of bioassays and present toxicity values for two bacteria, one alga, one euglena, three cladoceran, and two fish species that were exposed to Au-NPs. Guideline values for protecting aquatic ecosystems from Au-NPs were derived using methods that are generally used to derive water-quality guidelines and are used in Australia, New Zealand, Canada, the European Community (EC), and the USA. Au-NPs had adverse effects on all test species, including growth inhibition of both bacteria, the alga, and the euglena; mortality and immobilization in the three cladocerans; and developmental malformations in the embryos and larvae of the two fish. Guideline values of 0.15 and 0.04 × 10(10) particles/mL were derived for Au-NPs using a species sensitivity distribution (SSD) and assessment factor. The guideline value derived for Au-NPs using an assessment factor was more stringent than that derived using SSD. This is the first study to derive guideline values for nanoparticles in water environments.

Influence of aqueous media on the ROS-mediated toxicity of ZnO nanoparticles toward green fluorescent protein-expressing Escherichia coli under UV-365 irradiation

The aqueous media could affect the physicochemical properties (e.g., surface charge, morphology, and aggregation) of ZnO nanoparticles (nZnO), leading to their different environmental impacts. In this study, the toxicity of nZnO toward the green fluorescent protein-expressing Escherichia coli cells under UV-365 light irradiaiton in various media was assessed, including deionized (DI) water, 0.85% NaCl, phosphate-buffered saline (PBS), minimal Davis medium (MD), and Luria-Bertani medium (LB). The toxicity of nZnO was assessed by the conventional plate count method and the fluorescence intensity method, which consistently demonstrated that the nZnO toxicity was dependent on the medium components that varied the potency of reactive oxygen species (ROS) generation. In DI, NaCl, PBS, and MD medium, nZnO generated three types of ROS (O2(•-), •OH, and (1)O2), whereas in LB medium, nZnO generated O2(•-) and (1)O2. The total concentrations of ROS generated by nZnO in DI, NaCl, PBS, MD, and LB were 265.5 ± 15.9, 153.6 ± 8.6, 144.3 ± 6.9, 123.0 ± 6.0, and 115.6 ± 4.5 μM, respectively. Furthermore, a linear correlation was established between the total concentrations of three types of ROS generated by nZnO and their bacterial mortality rate (R(2) = 0.92) in various media. Since the released Zn(2+) from nZnO under UV irradiation only accounted for less than 10% of the total Zn in all media, the ionic forms of zinc did not significantly contribute to the overall toxicity. This work aims at providing further insight into the medium type influences on the ROS production and the toxicity of nZnO toward the E. coli cells.

Derivation of guideline values for gold (III) ion toxicity limits to protect aquatic ecosystems

This study focused on estimating the toxicity values of various aquatic organisms exposed to gold (III) ion (Au(3+)), and to propose maximum guideline values for Au(3+) toxicity that protect the aquatic ecosystem. A comparative assessment of methods developed in Australia and New Zealand versus the European Community (EC) was conducted. The test species used in this study included two bacteria (Escherichia coli and Bacillus subtilis), one alga (Pseudokirchneriella subcapitata), one euglena (Euglena gracilis), three cladocerans (Daphnia magna, Moina macrocopa, and Simocephalus mixtus), and two fish (Danio rerio and Oryzias latipes). Au(3+) induced growth inhibition, mortality, immobilization, and/or developmental malformations in all test species, with responses being concentration-dependent. According to the moderate reliability method of Australia and New Zealand, 0.006 and 0.075 mg/L of guideline values for Au(3+) were obtained by dividing 0.33 and 4.46 mg/L of HC5 and HC50 species sensitivity distributions (SSD) with an FACR (Final Acute to Chronic Ratio) of 59.09. In contrast, the EC method uses an assessment factor (AF), with the 0.0006 mg/L guideline value for Au(3+) being divided with the 48-h EC50 value for 0.60 mg/L (the lowest toxicity value obtained from short term results) by an AF of 1000. The Au(3+) guideline value derived using an AF was more stringent than the SSD. We recommend that more toxicity data using various bioassays are required to develop more accurate ecological risk assessments. More chronic/long-term exposure studies on sensitive endpoints using additional fish species and invertebrates not included in the current dataset will be needed to use other derivation methods (e.g., US EPA and Canadian Type A) or the "High Reliability Method" from Australia/New Zealand. Such research would facilitate the establishment of guideline values for various pollutants that reflect the universal effects of various pollutants in aquatic ecosystems. To the best of our knowledge, this is the first study to suggest guideline values for Au(3+) levels permitted to enter freshwater environments.

Synergistic bactericidal effect by combined exposure to Ag nanoparticles and UVA

Broad and strong antimicrobial properties of silver (Ag) have been used for biomedical applications, water treatment, etc. In this study, a synergistic antibacterial effect between Ag nanoparticles (AgNPs) and ultraviolet (UV) light was examined. AgNPs (<0.1 μm) with subsequent exposure to UVA (320-400 nm) showed pronounced toxicity in Escherichia coli, but micro-sized Ag particles (>1 μm) with UVA and AgNPs with UVB (280-325 nm) did not. As significant bactericidal activity was also exhibited by hydrogen peroxide-treated AgNPs, the surface oxidation of AgNPs caused by UVA irradiation was considered to contribute to the enhanced antibacterial effect. Although no difference in NP-incorporation rates was observed with or without the surface oxidation of AgNPs, a particle size of less than 0.1 μm was a factor for AgNPs uptake and an essential requirement for the antimicrobial function of Ag particles. Incorporated AgNPs oxidized by UVA irradiation released larger amounts of Ag ion inside cells than reduced AgNPs, which reacted with intercellular molecules having -SH groups such as glutathione. The synergistic use of AgNPs and UVA could become a powerful tool with broad antimicrobial applications.

Antibacterial and antibiofilm properties of yttrium fluoride nanoparticles

Antibiotic resistance has prompted the search for new agents that can inhibit bacterial growth. Moreover, colonization of abiotic surfaces by microorganisms and the formation of biofilms is a major cause of infections associated with medical implants, resulting in prolonged hospitalization periods and patient mortality. In this study we describe a water-based synthesis of yttrium fluoride (YF₃) nanoparticles (NPs) using sonochemistry. The sonochemical irradiation of an aqueous solution of yttrium (III) acetate tetrahydrate [Y(Ac)₃ · (H₂O)₄], containing acidic HF as the fluorine ion source, yielded nanocrystalline needle-shaped YF₃ particles. The obtained NPs were characterized by scanning electron microscopy and X-ray elemental analysis. NP crystallinity was confirmed by electron and powder X-ray diffractions. YF₃ NPs showed antibacterial properties against two common bacterial pathogens (Escherichia coli and Staphylococcus aureus) at a μg/mL range. We were also able to demonstrate that antimicrobial activity was dependent on NP size. In addition, catheters were surface modified with YF₃ NPs using a one-step synthesis and coating process. The coating procedure yielded a homogeneous YF₃ NP layer on the catheter, as analyzed by scanning electron microscopy and energy dispersive spectroscopy. These YF₃ NP-modified catheters were investigated for their ability to restrict bacterial biofilm formation. The YF₃ NP-coated catheters were able to significantly reduce bacterial colonization compared to the uncoated surface. Taken together, our results highlight the potential to further develop the concept of utilizing these metal fluoride NPs as novel antimicrobial and antibiofilm agents, taking advantage of their low solubility and providing extended protection.

Photoinduced damage to cellular DNA: direct and photosensitized reactions

The survey focuses on recent aspects of photochemical reactions to cellular DNA that are implicated through the predominant formation of mostly bipyrimidine photoproducts in deleterious effects of human exposure to sunlight. Recent developments in analytical methods have allowed accurate and quantitative measurements of the main DNA photoproducts in cells and human skin. Highly mutagenic CC and CT bipyrimidine photoproducts, including cyclobutane pyrimidine dimers and pyrimidine (6-4) pyrimidone photoproducts (6-4PPs) are generated in low yields with respect to TT and TC photoproducts. Another striking finding deals with the formation of Dewar valence isomers, the third class of bipyrimidine photoproducts that is accounted for by UVA-mediated isomerization of initially UVB generated 6-4PPs. Cyclobutadithymine (T<>T) has been unambiguously shown to be involved in the genotoxicity of UVA radiation. Thus, T<>T is formed in UVA-irradiated cellular DNA according to a direct excitation mechanism with a higher efficiency than oxidatively generated DNA damage that arises mostly through the Type II photosensitization mechanism. C<>C and C<>T are repaired at rates intermediate between those of T<>T and 6-4TT. Evidence has been also provided for the occurrence of photosensitized reactions mediated by exogenous agents that act either in an independent way or through photodynamic effects.