Search Results (18)

The goal of this work was to prepare modified titanium dioxide catalysts applicable for self-cleaning and disinfecting surfaces, possessing both antibacterial and photocatalytic activity in the visible-light region, via green and affordable synthesis. For this purpose, silverization was chosen due to its antibacterial and electron-capturing effects, and to achieve efficient visible-light excitation, urea was used as a precursor for nitrogen doping. Mechanochemical activation with grinding, as an environmentally friendly process, was applied for the catalyst modification under various conditions, such as the amounts of the modifying substances, the milling time, the ratio of the weights of the material to be ground, and the grinding balls. The photocatalytic activity in the UV and visible range was tested in suspensions with oxalic acid and coumarin as model compounds. The antibacterial effect was measured by the bioluminescence of Vibrio fischeri bacteria. The highest photocatalytic activity in the visible range was observed with the nitrogen-doped titanium dioxide (N-TiO₂) prepared with 10% urea. Silveration of N-TiO₂ (up to 0.2%) decreased photocatalytic activity while improving the antibacterial efficiency. To maximize both effects, mechanical mixtures of the separately modified catalysts (N-TiO₂ and Ag-TiO₂) were also examined in different ratios. The 1:1 mixture provided the optimum combination. Full article

Mycotoxin cocontamination is a severe threat to health and economic security worldwide. The mycotoxins aflatoxin B₁ (AFB₁), zearalenone (ZEN), deoxynivalenol, T-2 toxin, fumonisin B₁, and ochratoxin A are of particular concern due to their substantial toxicity. Lac-W is a laccase with the unique property of degrading these six mycotoxins in the absence of redox mediators. Nevertheless, their degradation rates are low. This work aims to improve the ability of Lac-W to degrade these six mycotoxins and to elucidate its detoxification mechanism. Including redox mediators increased the Lac-W degradation efficiency drastically, and completely degraded AFB₁ and ZEN within one hour. Additionally, Lac-W-AS has good temperature, pH, and ions adaptability in ZEN degradation. Lac-W-AS reduced the ZEN toxicity because ZEN degradation products significantly restored the bioluminescence intensity of Vibrio fischeri. A Lac-W-AS-mediated oxidation product of ZEN was structurally characterized as 15-OH-ZEN by UHPLC-MS/MS. Linear sweep voltammetry showed that AS affected the potential of Lac-W and accelerated the oxidation of ZEN. Finally, the combination of mediators (acetosyringone and 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonate)) improved the degradation rate of mycotoxins. This work highlights that the combination of Lac-W with mediators serves as a good candidate for degrading multi-mycotoxin contaminants in food and feedstuff. Full article

The quality of water supply systems is still a major problem in developing countries, especially in rural areas. The acute bioluminescence V. fischeri inhibition assay is widely recognized as a toxicological method that can be used to detect the acute effects of different contaminants. In this study, the physicochemical characteristics and toxicology of 72 water samples collected in 18 rural aqueducts located in Boyacá (Colombia) were evaluated. The primary economic activities identified as potential influencers of water quality in the water supply basins were agriculture (n = 3), livestock (n = 2), and domestic sewage discharge (n = 1). The average luminescence inhibition rate was 66%, with a minimum of 29%, and a maximum of 97%. A total of 85% of the tested samples (n = 61) had “moderate acute hazard”, while 15% (n = 15) had “acute hazard”. A total of 95% of the aqueducts distributed water with high risk. There was a weak positive correlation between the apparent color and the V. fischeri inhibition rate (p < 0.05). The water treatments, including disinfection, and the economic activities had no correlation with the inhibition rate of luminescent bacteria. The results of this investigation can be used by sanitary authorities to incorporate future toxicological monitoring of chemical contaminants, such as humic substances and metals, into water-quality monitoring in rural areas. Full article

The synthesis and structural characterization of synthetic zinc oxide and halloysite-based zinc oxide nanocomposites (with 2–28 m/m% ZnO content) are presented. The chemical precipitation of zinc hydroxide precursors and its subsequent drying at 80 °C yielded dominantly zinc oxide (zincite). Thermal treatment at 350 °C completely transformed the remaining precursor to ZnO without causing structural dehydroxylation of the halloysite support. The procedure yielded zinc oxide nanoparticles with 10–22 nm average size having quasi-spherical scale-like morphology. The specific surface area of the synthetic zinc oxide was found to be low (13 m²/g), which was significantly enhanced after nanocomposite preparation (27–47 m²/g). The photocatalytic activity of the prepared nanocomposites was probed by the degradation of a phenolic compound (4-nitrophenol) upon UV irradiation in liquid phase. Compared to their individual constituents, an increased activity of the nanocomposites was observed, while the SSA-normalized photocatalytic activity revealed a synergic effect in nanocomposites above 9 m/m% ZnO content. The nanocomposites were found to be stable at pH = 5.6, with a minor and major mobilization of zinc ions at pH = 12.4 and pH = 1.9, respectively. The toxicity of leachates in different pH environments by Vibrio fischeri bioluminescence indicated low toxicity for ZnO nanoparticles and insignificant toxicity for the nanocomposites. The enhanced photocatalytic activity together with the lower toxicity of the halloysite-ZnO nanocomposites highlight their application potential in water treatment. Full article

The Vibrio fischeri–Euprymna scolopes symbiosis has become a powerful model for the study of specificity, initiation, and maintenance between beneficial bacteria and their eukaryotic partner. In this invertebrate model system, the bacterial symbionts are acquired every generation from the surrounding seawater by newly hatched squid. These symbionts colonize a specialized internal structure called the light organ, which they inhabit for the remainder of the host’s lifetime. The V. fischeri population grows and ebbs following a diel cycle, with high cell densities at night producing bioluminescence that helps the host avoid predation during its nocturnal activities. Rhythmic timing of the growth of the symbionts and their production of bioluminescence only at night is critical for maintaining the symbiosis. V. fischeri symbionts detect their population densities through a behavior termed quorum-sensing, where they secrete and detect concentrations of autoinducer molecules at high cell density when nocturnal production of bioluminescence begins. In this review, we discuss events that lead up to the nocturnal acidification of the light organ and the cues used for pre-adaptive behaviors that both host and symbiont have evolved. This host–bacterium cross talk is used to coordinate networks of regulatory signals (such as quorum-sensing and bioluminescence) that eventually provide a unique yet stable environment for V. fischeri to thrive and be maintained throughout its life history as a successful partner in this dynamic symbiosis. Full article

Commonly used as biological chemosensors in toxicity assays, Vibrio fischeri bacteria were systematically characterized using complementary physicochemical and biological techniques to elucidate the evolution of their properties under varying environmental conditions. Changing the pH above or below the optimal pH 7 was used to model the long-term stress that would be experienced by V. fischeri in environmental toxicology assays. The spectral shape of bioluminescence and cell-surface charge during the exponential growth phase were largely unaffected by pH changes. The pH-induced modulation of V. fischeri growth, monitored via the optical density (OD), was moderate. In contrast, the concomitant changes in the time-profiles of their bioluminescence, which is used as the readout in assays, were more significant. Imaging at discrete timepoints by scanning electron microscopy (SEM) and helium-ion microscopy (HIM) revealed that mature V. fischeri cells maintained a rod-shaped morphology with the average length of 2.2 ± 1 µm and diameter of 0.6 ± 0.1 µm. Detailed morphological analysis revealed subpopulations of rods having aspect ratios significantly larger than those of average individuals, suggesting the use of such elongated rods as an indicator of the multigenerational environmental stress. The observed modulation of bioluminescence and morphology supports the suitability of V. fischeri as biological chemosensors for both rapid and long-term assays, including under environmental conditions that can modify the physicochemical properties of novel anthropogenic pollutants, such as nanomaterials and especially stimulus-responsive nanomaterials. Full article

This study evaluates the impacts of 16 different leachates of plastic-made packaging on marine species of different trophic levels (bacteria, algae, echinoderms). Standard ecotoxicological endpoints (inhibition of bioluminescence, inhibition of growth, embryo-toxicity) and alterations of ecologically significant parameters (i.e., echinoderms’ body-size) were measured following exposure under different pH water conditions: marine standard (pH 8.1) and two increasingly acidic conditions (pH 7.8 and 7.5) in order to evaluate possible variations induced by ocean acidification. The results obtained in this study evidence that the tested doses are not able to significantly affect bacteria (Vibrio fischeri) and algae (Phaeodactylum tricornutum). On the contrary, Paracentrotus lividus larvae were significantly affected by several packaging types (13 out of 16) with meaningless differences between pH conditions. Full article

In the current study, the antibacterial activity of positively and negatively charged spherical hematite (α-Fe₂O₃) nanoparticles (NPs) with primary size of 45 and 70 nm was evaluated against clinically relevant bacteria Escherichia coli (gram-negative) and Staphylococcus aureus (gram-positive) as well as against naturally bioluminescent bacteria Vibrio fischeri (an ecotoxicological model organism). α-Fe₂O₃ NPs were synthesized using a simple green hydrothermal method and the surface charge was altered via citrate coating. To minimize the interference of testing environment with NP’s physic-chemical properties, E. coli and S. aureus were exposed to NPs in deionized water for 30 min and 24 h, covering concentrations from 1 to 1000 mg/L. The growth inhibition was evaluated following the postexposure colony-forming ability of bacteria on toxicant-free agar plates. The positively charged α-Fe₂O₃ at concentrations from 100 mg/L upwards showed inhibitory activity towards E. coli already after 30 min of contact. Extending the exposure to 24 h caused total inhibition of growth at 100 mg/L. Bactericidal activity of positively charged hematite NPs against S. aureus was not observed up to 1000 mg/L. Differently from positively charged hematite NPs, negatively charged citrate-coated α-Fe₂O₃ NPs did not exhibit any antibacterial activity against E. coli and S. aureus even at 1000 mg/L. Confocal laser scanning microscopy and flow cytometer analysis showed that bacteria were more tightly associated with positively charged α-Fe₂O₃ NPs than with negatively charged citrate-coated α-Fe₂O₃ NPs. Moreover, the observed associations were more evident in the case of E. coli than S. aureus, being coherent with the toxicity results. Vibrio fischeri bioluminescence inhibition assays (exposure medium 2% NaCl) and colony forming ability on agar plates showed no (eco)toxicity of α-Fe₂O₃ (EC₅₀ and MBC > 1000 mg/L). Full article

Terpenoids, including monoterpenoids (C₁₀), norisoprenoids (C₁₃), and sesquiterpenoids (C₁₅), constitute a large group of plant-derived naturally occurring secondary metabolites with highly diverse chemical structures. A quantitative structure–activity relationship (QSAR) model to predict terpenoid toxicity and to evaluate the influence of their chemical structures was developed in this study by assessing in real time the toxicity of 27 terpenoid standards using the Gram-negative bioluminescent Vibrio fischeri. Under the test conditions, at a concentration of 1 µM, the terpenoids showed a toxicity level lower than 5%, with the exception of geraniol, citral, (S)-citronellal, geranic acid, (±)-α-terpinyl acetate, and geranyl acetone. Moreover, the standards tested displayed a toxicity level higher than 30% at concentrations of 50–100 µM, with the exception of (+)-valencene, eucalyptol, (+)-borneol, guaiazulene, β-caryophellene, and linalool oxide. Regarding the functional group, terpenoid toxicity was observed in the following order: alcohol > aldehyde ~ ketone > ester > hydrocarbons. The CODESSA software was employed to develop QSAR models based on the correlation of terpenoid toxicity and a pool of descriptors related to each chemical structure. The QSAR models, based on t-test values, showed that terpenoid toxicity was mainly attributed to geometric (e.g., asphericity) and electronic (e.g., maximum partial charge for a carbon (C) atom (Zefirov’s partial charge (PC)) descriptors. Statistically, the most significant overall correlation was the four-parameter equation with a training coefficient and test coefficient correlation higher than 0.810 and 0.535, respectively, and a square coefficient of cross-validation (Q²) higher than 0.689. According to the obtained data, the QSAR models are suitable and rapid tools to predict terpenoid toxicity in a diversity of food products. Full article

The increasing amount of hazardous micropollutants in the aqueous environment has recently become a concern, especially because they are not usually included in environmental monitoring programs. There is also limited knowledge regarding their behavior in the environment and their toxicity. This paper presents results regarding the heterogeneous photosensitized oxidation of 10 phenolic compounds under visible light. All of the selected compounds are classified as pollutants of emerging concern. For the first time, the application of photosensitizing catalysts incorporated into a chitosan carrier was investigated from several points of view, namely, structure characterization, singlet oxygen generation potential, photodegradation ability, biodegradability, and toxicity assessment. It was found that compounds of different origins were degraded with high effectivity. Photoactive chitosan was stable and could be reused for at least 12 cycles without losing its photocatalytic activity. The Hammett constants for all of the degraded compounds were determined. Improved biodegradability after the treatment was achieved for almost all compounds, apart from 4-hydroxybenzoic acid, and only slightly for 2-phenylphenol. The acute toxicity was assessed using bioluminescent Vibrio fischeri bacteria, indicating lower toxicity than the parent compounds. Full article

Food packaging materials constitute an ever more threatening environmental pollutant. This study examined options to specifically assess the ecotoxicity of packaged wastes, such as cans, subjected to various experimental treatments (in terms of extraction media, time of exposure, and temperature) that imitate several basic conditions of the process of food production. The extracts were studied for their ecotoxicity with bioluminescent Vibrio fischeri bacteria. The first objective of this study was to find patterns of similarity between different experimental conditions; we used multivariate statistical methods, such as hierarchical cluster analysis, to interpret the impact of experimental conditions on the ecotoxicity signals of the package extracts. Our second objective was to apply best-fit function modelling for additional data interpretation, taking into account, that ecotoxicity for various temperature conditions is time- and temperature dependent. We mathematically confirmed that chemometric data treatment allows for better understanding how different experimental conditions imitating the real use of food packaging. We also demonstrate that the level of ecotoxicity depends on different extraction media, time of exposure, and temperature regime. Full article

The ecotoxicity of a nitrate-based ionic liquid (IL) and saturated mixtures with four nitrate salts towards the bioluminescent bacteria Vibrio fischeri, were tested in this work, using the Microtox^® standard toxicity test. The selected IL was Ethylammonium Nitrate (EAN) and the nitrate salts were Lithium Nitrate (LiNO₃), Calcium Nitrate (Ca(NO₃)₂), Magnesium Nitrate (Mg(NO₃)₂), and Aluminum Nitrate (Al(NO₃)₃). The effective concentration (EC₅₀) of these mixtures was determined over three standard periods of time, namely 5, 15, and 30 min. Results of EC₅₀ for pure EAN at 15 min are in relatively good concordance with the literature. To the best of our knowledge, no ecotoxicity studies have been performed for doped EAN. Similar results have been found for pure EAN and for EAN doped with LiNO₃ and Mg(NO₃)₂, whose values indicated low toxicity. Nevertheless, the addition of Ca(NO₃)₂ and Al(NO₃)₃ cause an increase in the ecotoxicity of EAN, especially for the IL doped with Al(NO₃)₃, which present values associated to highly toxic compounds, comparable even with benzene or atrazine. Full article

Despite the increasing use of rare earth elements (REEs) and oxides (REOs) in various technologies, the information on their ecotoxicological hazard is scarce. Here, the effects of La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Gd³⁺, CeO₂, and eight doped REOs to marine bacteria Vibrio fischeri and freshwater protozoa Tetrahymena thermophila were studied in parallel with REO dopant metals (Co²⁺, Fe³⁺, Mn²⁺, Ni²⁺, Sr²⁺). The highest concentrations of REOs tested were 100 mg/L with protozoa in deionized water and 500 mg/L with bacteria in 2% NaCl. Although (i) most REOs produced reactive oxygen species; (ii) all studied soluble REEs were toxic to bacteria (half-effective concentration, EC₅₀ 3.5–21 mg metal/L; minimal bactericidal concentration, MBC 6.3–63 mg/L) and to protozoa (EC₅₀ 28–42 mg/L); and (iii) also some dopant metals (Ni²⁺, Fe³⁺) proved toxic (EC₅₀ ≤ 3 mg/L), no toxicity of REOs to protozoa (EC₅₀ > 100 mg/L) and bacteria (EC₅₀ > 500 mg/L; MBC > 500 mg/L) was observed except for La₂NiO₄ (MBC 25 mg/L). According to kinetics of V. fischeri bioluminescence, the toxicity of REEs was triggered by disturbing cellular membrane integrity. Fortunately, as REEs and REOs are currently produced in moderate amounts and form in the environment insoluble salts and/or oxides, they apparently present no harm to aquatic bacteria and protozoa. Full article

A bioluminescent-cell-based microfluidic device for sensing toxicants in drinking water was designed and fabricated. The system employed Vibrio fischeri cells as broad-spectrum sensors to monitor potential systemic cell toxicants in water, such as heavy metal ions and phenol. Specifically, the chip was designed for continuous detection. The chip design included two counter-flow micromixers, a T-junction droplet generator and six spiral microchannels. The cell suspension and water sample were introduced into the micromixers and dispersed into droplets in the air flow. This guaranteed sufficient oxygen supply for the cell sensors. Copper (Cu²⁺), zinc (Zn²⁺), potassium dichromate and 3,5-dichlorophenol were selected as typical toxicants to validate the sensing system. Preliminary tests verified that the system was an effective screening tool for acute toxicants although it could not recognize or quantify specific toxicants. A distinct non-linear relationship was observed between the zinc ion concentration and the Relative Luminescence Units (RLU) obtained during testing. Thus, the concentration of simple toxic chemicals in water can be roughly estimated by this system. The proposed device shows great promise for an early warning system for water safety. Full article

We show that in vitro toxicity assay based on inhibition of the bioluminescence of recombinant Escherichia coli encoding thermostable luciferase from Photorhabdus luminescens is a versatile alternative to Vibrio fischeri Microtox^TM test. Performance of two luxCDABE-transformed E. coli MC1061 constructs (pDNlux) and (pSLlux) otherwise identical, but having 100-fold different background luminescence was compared with the performance of V. fischeri. The microplate luminometer and a kinetic Flash-Assay test format was used that differently from Microtox test is also applicable for high throughput analysis. Toxic effects (30-s till 30-min EC₅₀) of four heavy metals (Zn, Cd, Hg, Cu) and three organic chemicals (aniline, 3,5-dichloroaniline and 3,5-dichlorophenol) were studied. Both E. coli strains had comparable sensitivity and the respective 30-min EC₅₀ values highly correlated (log-log R² = 0.99; p < 0.01) showing that the sensitivity of the recombinant bacteria towards chemicals analyzed did not depend on the bioluminescence level of the recombinant cells. The most toxic chemical for all used bacterial strains (E. coli, V. fischeri) was mercury whereas the lowest EC₅₀ values for Hg (0.04–0.05 mg/L) and highest EC₅₀ values for aniline (1,300–1,700 mg/L) were observed for E. coli strains. Despite of that, toxicity results obtained with both E. coli strains (pSLlux and pDNlux) significantly correlated with V. fischeri results (log-log R² = 0.70/0.75; p < 0.05/0.01). The use of amino acids (0.25%) and glucose (0.05%)-supplemented M9 medium instead of leucine-supplemented saline significantly (p < 0.05) reduced the apparent toxicity of heavy metals to both E. coli strains up to three orders of magnitude, but had little or no complexing effect on organic compounds. Thus, P. luminescens luxCDABE-transformed E. coli strains can be successfully used for the acute toxicity screening of various types of organic chemicals and heavy metals and can replace V. fischeri in certain cases where the thermostability of luciferase >30 °C is crucial. The kinetic Flash Assay test format of the bioluminescence inhibition assay facilitates high throughput analysis. The assay medium, especially in case of testing heavy metals should be a compromise: optimal for the viability/luminescence of the recombinant test strain and of minimum complexing potential. Full article