In vivo estrogenicity of glyphosate, its formulations, and AMPA on transgenic zebrafish (Danio rerio) embryos

In this study, the disrupting effects of glyphosate (GLY), aminomethylphosphonic acid (AMPA), and three glyphosate-based herbicides (GBHs) on vitellogenesis in a non-concentration-dependent manner are reported for the first time in 120 h of acute exposure of zebrafish at environmentally relevant concentrations. GBHs are commonly used worldwide in weed control management. Due to their extensive application, they frequently occur in aquatic ecosystems and may affect various organisms. The active substance GLY and its major by-product, AMPA, are the most thoroughly studied chemicals; however, the adverse effects of the complex formulas of GBHs with diverse and unknown content of co-formulants are still not sufficiently researched. This study focused on the embryotoxicity, sublethal malformations, and estrogenic potency of GLY, AMPA, and four commonly used GBHs on zebrafish embryos using a wild type and an estrogen-sensitive, transgenic zebrafish line (Tg(vtg1:mCherry)). After 120 h of exposition, AMPA did not cause acute toxicity, while the LC50 of GLY was 160 mg/L. The GBHs were more toxic with LC50 values ranging from 31 to 111 GLY active equivalent (a.e.) mg/L. Exposure to 0.35-2.8 mg/L GBHs led to sublethal abnormalities: typical symptoms were structural deformation of the lower jaw and anomalies in the olfactory region. Deformity rates were 10-30% in the treated groups. In vivo, fluorescently expressed vtg1 mCherry protein in embryonic liver was detected by a non-invasive microscopic method indicating estrogenic action through vitellogenin production by GLY, AMPA, and GBHs. To confirm the in vivo findings, RT-qPCR method was performed to determine the levels of the estrogenicity-related vtg1 mRNA. After 120 h of exposure to GLY, AMPA, and three GBHs at a concentration of 0.35 mg/L, the expression of vtg1 gene was significantly up-regulated. Our results highlight the risk that short-term GLY and GBH exposure can cause developmental malformations and disrupt the hormonal balance in zebrafish embryos.

Cyanobacterial bioreporter of nitrate bioavailability in aquatic ecosystems

The water eutrophication, resulting from the discharge of industrial and agricultural wastewater, leads to ecological degradation. However, to date, how to assess and manage the risks of water pollution, especially nitrogen pollution, remains a particularly noteworthy issue. Nitrate, the most important nitrogen compound, has become a bottleneck restricting total nitrogen management. The development of bioreporters monitoring nitrate pollution contributes to the estimation of water quality, especially the availability of nutrients. In this study, we obtained 9 bioreporters from 40 cyanobacterial derivatives which were constructed based on different hosts, copy numbers, and sensing elements and evaluated the performance of bioreporters. The results showed that single-celled Synechocystis was more sensitive to nitrate than filamentous Anabaena, that the reporter gene luxABCDE responded faster than sfgfp in most bioreporters, and that relatively medium-copy plasmid improved the performance of sensing elements. Nine bioreporters performed well in bioavailable nitrate detection, of which AD-AS-X and AR-NI-X, activated by nitrate repletion, had the shortest response time (2 h) and the widest response range (20-800 μM), respectively. Moreover, SR-GLN-SG, activated by nitrate deficiency, exhibited the best linear response (R2 = 0.998). After parameter optimization, exponential growth phase bioreporters, culture temperature of 30 °C, sample volume of 200 μL were determined as optimal monitoring conditions. We found that common water contaminants (copper, cadmium, and phosphorus) had no impact on the performance of bioreporters, indicating the stability of bioreporters. Six out of 9 bioreporters, especially the SR-NB-X, were highly effective in detecting the bioavailable nitrate in wastewater sample. This study provides valuable references for developing more cyanobacterial bioreporters and their practical application in nitrate detection.

Online detection of alkanes by a biological-phase microextraction and biosensing (BPME-BS) device

Oil spill incidents occur frequently and threaten ecosystems and human health. Solid-phase microextraction allows direct alkane extraction from environmental matrices to improve the limit of detection but is unable to measure alkanes on site. A biological-phase microextraction and biosensing (BPME-BS) device was developed by immobilising an alkane chemotactic Acinetobacter bioreporter ADPWH_alk in agarose gel to achieve online alkane quantification with the aid of a photomultiplier. The BPME-BS device had a high enrichment factor (average 7.07) and a satisfactory limit of detection (0.075 mg/L) for alkanes. The quantification range was 0.1-100 mg/L, comparable to a gas chromatography flame ionisation detector and better than a bioreporter without immobilisation. ADPWH_alk cells in the BPME-BS device maintained good sensitivity under a wide range of environmental conditions, including pH (4.0-9.0), temperature (20-40 °C), and salinity (0.0-3.0%), and its response remained stable within 30 days at 4 °C. In a 7-day continual measurement, the BPME-BS device successfully visualised the dynamic concentration of alkanes, and a 7-day field test successfully captured an oil spill event, helping in source apportionment and on-scene law enforcement. Our work proved that the BPME-BS device is a powerful tool for online alkane measurement, showing substantial potential for fast detection and rapid response to oil spills on site and in situ.

Pandemic COVID-19 ends but soil pollution increases: Impacts and a new approach for risk assessment

For three years, a large amount of manufactured pollutants such as plastics, antibiotic and disinfectant has been released into the environment due to COVID-19. The accumulation of these pollutants in the environment has exacerbated the damage to the soil system. However, since the epidemic outbreak, the focus of researchers and public attention has consistently been on human health. It is noteworthy that studies conducted in conjunction with soil pollution and CIVID-19 represent only 4 % of all COVID-19 studies. In order to enhance researchers' and the public awareness of the seriousness on the COVID-19 derived soil pollution, we propose the viewpoint that "pandemic COVOD-19 ends but soil pollution increases" and recommend a whole-cell biosensor based new method to assess the environmental risk of COVID-19 derived pollutants. This approach is expected to provide a new way for environmental risk assessment of soils affected by contaminants produced from pandemic.

Paleoecotoxicology: Developing methods to assess the toxicity of lake sediment records influenced by legacy gold mining

The contamination of lakes by industrial emissions is an issue of international concern. Traditional paleolimnology examines sedimentary micro-fossils to infer the biological response to natural and anthropogenic stressors over time. Here, we calculate a theoretical biological effect for historic sediment sections using Probable Effect Concentration Quotient (PEC-Q) and arsenic specific quotient methods and develop novel time-constrained sediment toxicity test methods using a cultured Daphnia sp. combined with a whole cell microbial biosensor to assess the toxicity of past industrial contamination with modern testing methods. These methods were developed using sediments collected from Pocket Lake (Northwest Territories, Canada), a lake known to have exhibited a significant ecological shift following input from nearby gold smelter emissions during the mid 20th century. We then applied these methods to near-, mid-, and far-field sites to assess the response of Daphnia sp. to varying contaminant load. Daphnia sp. mortality exposed to dated sediments indicated a strong concordance with the timing of mining activities, and a strong concordance with PEC-Q and arsenic specific toxicity quotients. In contrast, a decrease in Daphnia mortality was observed during pre-, and post-mining periods when the contaminant burden was lower. Initial assessments of bioavailability using a microbial biosensor indicated that arsenic in porewater is 72-96% bioavailable, and limited evidence that oxidative stress may contribute to the Daphnia sp. toxic response. These results indicate that lake sediment archives can be used to infer missing biomonitoring data in sites of legacy anthropogenic influence, which will be useful for those seeking to conduct cost-effective and efficient preliminary environmental risk assessments.

Whole-cell biosensors for determination of bioavailable pollutants in soils and sediments: Theory and practice

The bioavailability of pollutants is a key factor affecting environmental risk. Whole-cell bioreporters are a demonstratedly effective tool for the investigation of pollutant bioavailability in water and soil/sediment. Unlike aqueous samples, transmittance of bioreporter optical signal is reduced in direct-contact assays with soil/sediment, which affects the accuracy of bioreporter-detected pollutant bioavailability. No studies have measured the magnitude and variability of soil/sediment effects on signal in direct-contact assays or how associated uncertainties influence results. In this study, we investigate the optical effects of soil/sediment particles in suspensions on bioreporter signal transmittance and quantify how variable these optical effects are from sample-to-sample. We find that neglecting bioreporter signal diminution by soil/sediment, as many studies do, can lead to order-of-magnitude errors in results, underestimating risk. Correction based on methods in ad hoc use (e.g. comparison to signal from non-inducible reporter or use of reference soil/sediment) are also problematic for some types of experiment, and could lead to errors in excess of 30%. Our findings have a sound basis in theory, and we provide recommendations concerning the most suitable type of approach to use for different experimental settings. Generally, if best accuracy is not needed to quantify bioavailability, for samples that have been ground, sieved, and are of reasonably uniform color, it may be possible to use a single or average correction factor, particularly for experiments performed at a single slurry concentration. For investigations studying bioavailability under varying solid-phase:water ratios (e.g., sorption/desorption), detailed compensation measurements are needed for independent variables, including each specific soil/sediment sample, slurry concentration, and in some cases bioreporter signal intensity. Our measurements and calculations indicate that best results are obtained when working in the region of ballistic photon transmittance. Findings herein will be useful in areas that require information on bioavailability, such as ecotoxicology and environmental risk assessment.

Screening of metallic pollution in complex environmental samples through a transcriptomic fingerprint method

Characterizing waste ecotoxicity is laborious because of both the undefined nature of environmental samples and the diversity of contaminants that can be present. With regard to these limitations, traditional approaches do not provide information about the nature of the pollution encountered. To improve such assessments, a fluorescent library of 1870 transcriptomic reporters from Escherichia coli K12 MG1655 was used to report the ecotoxic status of environmental samples. The reliability of the approach was evaluated with 6 metallic pollutants (As, Cu, Cd, Hg, Pb, Zn) used alone and in mixture in pure and complex matrices. A total of 18 synthetic samples were used to characterize the specificity of the resulting metallic contamination fingerprints. Metallic contamination impacted 4.5 to 10.2% of the whole transcriptomic fingerprint of E. coli. The analysis revealed that a subset of 175 transcriptomic reporters is sufficient to characterize metallic contamination, regardless of the nature of the sample. A statistical model distinguished patterns due to metallic contamination and provided information about the level of toxicity with 93 to 98% confidence. The use of the transcriptomic assessment was validated for 17 complex matrices with various toxicities and metal contaminants, such as activated sludge, wastewater effluent, soil, wood and river water. The presence of metals and their associated toxicity, which seems linked to their bioavailabilities, were thereby determined. This method constitutes a possible tool to screen unknown complex samples for their metallic status and identify those for which a deeper characterization must be achieved by the use of traditional biosensors and analytical methods.

Carbon starvation of Pseudomonas aeruginosa biofilms selects for dispersal insensitive mutants

BACKGROUND

Biofilms disperse in response to specific environmental cues, such as reduced oxygen concentration, changes in nutrient concentration and exposure to nitric oxide. Interestingly, biofilms do not completely disperse under these conditions, which is generally attributed to physiological heterogeneity of the biofilm. However, our results suggest that genetic heterogeneity also plays an important role in the non-dispersing population of P. aeruginosa in biofilms after nutrient starvation.

RESULTS

In this study, 12.2% of the biofilm failed to disperse after 4 d of continuous starvation-induced dispersal. Cells were recovered from the dispersal phase as well as the remaining biofilm. For 96 h starved biofilms, rugose small colony variants (RSCV) were found to be present in the biofilm, but were not observed in the dispersal effluent. In contrast, wild type and small colony variants (SCV) were found in high numbers in the dispersal phase. Genome sequencing of these variants showed that most had single nucleotide mutations in genes associated with biofilm formation, e.g. in wspF, pilT, fha1 and aguR. Complementation of those mutations restored starvation-induced dispersal from the biofilms. Because c-di-GMP is linked to biofilm formation and dispersal, we introduced a c-di-GMP reporter into the wild-type P. aeruginosa and monitored green fluorescent protein (GFP) expression before and after starvation-induced dispersal. Post dispersal, the microcolonies were smaller and significantly brighter in GFP intensity, suggesting the relative concentration of c-di-GMP per cell within the microcolonies was also increased. Furthermore, only the RSCV showed increased c-di-GMP, while wild type and SCV were no different from the parental strain.

CONCLUSIONS

This suggests that while starvation can induce dispersal from the biofilm, it also results in strong selection for mutants that overproduce c-di-GMP and that fail to disperse in response to the dispersal cue, starvation.

High-Throughput Analysis of Endocrine-Disrupting Compounds Using BLYES and BLYAS Bioluminescent Yeast Bioassays

Bioluminescent yeast assays BLYES and BLYAS are whole-cell bioassays that utilize genetically modified Saccharomyces cerevisiae bioreporters to detect estrogenic and androgenic activities, respectively. The bioreporter strains chromosomally express human estrogen receptor alpha (BLYES) or androgen receptor (BLYAS) and contain a reporter plasmid expressing the complete bacterial luciferase gene cassette (luxCDABE) under the control of an estrogen- or androgen-responsive promoter. Exposure to endocrine-disrupting compounds activates the receptor which subsequently turns on the expression of the reporter genes, resulting in dose-dependent bioluminescence (i.e., light) emission. These yeast whole-cell bioassays provide rapid, cost-effective, and high-throughput detection of endocrine-disrupting activities in environmental samples. This protocol will provide a detailed description of the standard assay procedures as well as a framework for data analysis.

Peroxiredoxin (2-cys-prx) and catalase (katA) cyanobacterial-based bioluminescent bioreporters to detect oxidative stress in the aquatic environment

The detection of oxidative stress caused by emerging pollutants in aquatic systems is essential to carry out toxicological analysis since they can bring us information about the mechanisms of toxic action of the pollutants, which might be useful to address this contamination. To achieve this goal, two self-bioluminescent strains that respond to oxidative stress based on the filamentous cyanobacterium Nostoc sp. PCC7120, which has a high ecological relevance in aquatic continental systems, have been constructed. Nostoc sp. PCC7120 pBG2172 harbours the promoter region of the 2-cys-prx gene (P2-cys-prx), encoding a cytoplasmic peroxiredoxin, fused to luxCDABE genes of the bacterium Photorhabdus luminescens. Nostoc sp. PCC7120 pBG2173 harbours the promoter region of the KatA gene (PkatA), a cytoplasmic catalase, also fused to luxCDABE genes. Both strains have been characterized by exposing them to H₂O₂: Nostoc sp. PCC7120 pBG2172 responded while Nostoc sp. PCC7120 pBG2173 did not respond to this pollutant. In order to know their specificity, they were exposed to methyl viologen (MV), an herbicide that produces superoxide anion (O₂^-) and a bioluminescence response was observed in both strains. Besides, the utility of these strains for the detection of H₂O₂ and MV in natural water samples, both pristine and wastewater samples has been tested by spiking experiments. Finally, the possible application of these strains for the detection of the emerging pollutant triclosan has also been tested showing to be suitable bioreporters to study oxidative stress in aquatic environments.

The involvement of superoxide radicals in medium pressure UV derived inactivation

Today, two types of lamp systems dominate the UV disinfection industry: low-pressure (LP) UV lamps and medium-pressure (MP) polychromatic lamps. Both lamp types have their advantages and disadvantages in microorganism inactivation, with LP lamps being cheaper, having longer life, and working at lower temperature, hence reducing fouling, and MP lamps showing better inactivation per germicidal dose for certain microorganisms. Bacterium-based biosensors were used to compare LP and MP irradiation. These biosensors were Escherichia coli bacteria carrying the lux operon genes under the control of different stress-responding promoters, where activation of the specific promoter is manifested as bioluminescence. MP irradiation, considerably more than LP irradiation, resulted in activation of the superoxide dismutase expression, indicating the formation of superoxide radicals inside the cells. Accordingly, pre-exposure (immunization) of the bacteria to an activator that produces superoxide radicals resulted in lower inactivation and increased resistance to MP irradiation, but not to LP irradiation. This study shows that the difference in germicidal efficiency may result from the production of intracellular superoxide radicals by MP irradiation, at wavelengths other than 254 nm, as emitted by LP lamps.

Rapid and efficient protocol to introduce exogenous DNA in Vibrio harveyi and Pseudoalteromonas sp

Vibrio campbellii BAA-1116 is renowned for its bioluminescence properties, and genetic tools are available to genetically track this strain. However, many other ecologically important V. harveyi strains exist, for which only few genetic tools are available. In this study, a rapid electroporation protocol was developed to transform replicative plasmids in various environmental V. harveyi and Pseudoalteromonas strains. Moreover, a mini-Tn7 delivery system was modified to site-specifically integrate mini-transposons in the genome of V. harveyi ORM4. As a proof-of-principle, replicative plasmids carrying bioreporters were introduced by electroporation in V. harveyi ORM4 cells, and gene expression was followed at the single cell level. We could demonstrate that a flagellar gene is subjected to bimodal gene expression in V. harveyi ORM4, being highly expressed in 10% of the population in stationary phase. This study extends the possibilities to study environmental Vibrio strains and uncovers the occurrence of phenotypic heterogeneity in flagellar expression in Vibrio.

A rapid and reagent-free bioassay for the detection of dioxin-like compounds and other aryl hydrocarbon receptor (AhR) agonists using autobioluminescent yeast

An autonomously bioluminescent Saccharomyces cerevisiae BLYAhS bioreporter was developed in this study for the simple and rapid detection of dioxin-like compounds (DLCs) and aryl hydrocarbon receptor (AhR) agonists. This recombinant yeast reporter was based on a synthetic bacterial luciferase reporter gene cassette (lux) that can produce the luciferase as well as the enzymes capable of self-synthesizing the requisite substrates for bioluminescent production from endogenous cellular metabolites. As a result, bioluminescent signal production is generated continuously and autonomously without cell lysis or exogenous reagent addition. By linking the expression of the autobioluminescent lux reporter cassette to AhR activation via the use of a dioxin-responsive promoter, the S. cerevisiae BLYAhS bioreporter emitted a bioluminescent signal in response to DLC exposure in a dose-responsive manner. The model dioxin, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), could be detected within 4 h with a half maximal effective concentration (EC₅₀) of ~ 8.1 nM and a lower detection limit of 500 pM. The autobioluminescent response of BLYAhS to other AhR agonists, including 2,3,7,8-tetrachlorodibenzofuran (TCDF), polychlorinated bisphenyl congener 126 (PCB-126) and 169 (PCB-169), 1,2,3,6,7,8-hexachlorodibenzo-p-dioxin (HxCDD), 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin (HpCDD), benzo[a]pyrene (BaP), and β-naphthoflavone (bNF), were also characterized in this study. The non-destructive and reagent-free nature of the BLYAhS reporter assay facilitated near-continuous, automated signal acquisition without additional hands-on effort and cost, providing a simple and cost-effective method for rapid DLC detection.

Application of the freeze-dried bioluminescent bioreporter Pseudomonas putida mt-2 KG1206 to the biomonitoring of groundwater samples from monitoring wells near gasoline leakage sites

This study examined the applicability of a freeze-dried bioluminescent bioreporter, Pseudomonas putida mt-2 KG1206 (called KG1206), to the biomonitoring of groundwater samples. Samples were collected from the monitoring wells of gas station tanks or old pipeline leakage sites in Korea. In general, the freeze-dried strain in the presence of pure inducer chemicals showed low bioluminescence activity and a different activity order compared with that of the subcultured strain. The effects of KNO₃ as a bioluminescence stimulant were observed on the pure inducers and groundwater samples. The stimulation rates varied according to the type of inducers and samples, ranging from 2.2 to 20.5 times (for pure inducers) and from 1.1 to 11 times (for groundwater samples) the total bioluminescence of the control. No considerable correlations were observed between the bioluminescence intensity of the freeze-dried strain and the inducer concentrations in the samples (R ² < 0.1344). However, samples without a high methyl tertiary butyl ether (MTBE) level and those from the gas station leakage site showed reasonable correlations with the bioluminescence activity with R ² values of 0.3551 and 0.4131, respectively. These results highlight the potential of using freeze-dried bioluminescent bacteria as a rapid, simple, and portable tool for the preliminary biomonitoring of specific pollutants at contaminated sites.

Microbial availability of mercury: effective detection and organic ligand effect using a whole-cell bioluminescent bioreporter

A luxCDABE-based genetically engineered bacterial bioreporter (Escherichia coli ARL1) was used to detect bioavailable ionic mercury (Hg(II)) and investigate the effects of humic acids and ethylenediaminetetraacetic acid (EDTA) on the bioavailability of mercury in E. c oli. Results showed that the E. c oli ARL1 bioreporter was sensitive to mercury, with a detection limit of Hg(II) of 0.5 µg/L and a linear dose/response relationship up to 2000 µg Hg(II)/L. Humic acids and EDTA decreased the Hg(II)-induced bioluminescent response of strain ARL1, suggesting that the two organic ligands reduced the bioavailability of Hg(II) via complexation with Hg(II). Compared with traditional chemical methods, the use of E. c oli ARL1 is a cost-effective, rapid, and reliable approach for measuring aqueous mercury at very low concentrations and thus has potential for applications in field in situ monitoring.

Biological toxicity of cellulose nanocrystals (CNCs) against the luxCDABE-based bioluminescent bioreporter Escherichia coli 652T7

The aim of this study was to evaluate the biological toxicity of cellulose nanocrystals (CNCs) using the constitutively bioluminescent luxCDABE-based bioreporter Escherichia coli 652T7. The effects of CNCs on E. c oli 652T7 biotoxicity were investigated at different CNC concentrations, reaction times, and IC50 values. CNC toxicity was also compared with and without ultrasonic dispersion to establish dispersibility effects. The results demonstrated that CNCs were not significantly toxic at concentrations at or below 250 mg/L. At concentrations higher than 300 mg/L, toxicity increased linearly as CNC concentrations increased up to 2000 mg/L. IC50 calculations demonstrated an increase in cytotoxicity as CNC exposure times increased, and elevated dispersibility of the CNCs were shown to increase cytotoxicity effects. These results suggest that CNCs can impact microbial populations if elevated concentration thresholds are met.

Bioluminescent bioreporter pad biosensor for monitoring water toxicity

Toxicants in water sources are of concern. We developed a tool that is affordable and easy-to-use for monitoring toxicity in water. It is a biosensor composed of disposable bioreporter pads (calcium alginate matrix with immobilized bacteria) and a non-disposable CMOS photodetector. Various parameters to enhance the sensor's signal have been tested, including the effect of alginate and bacterium concentrations. The effect of various toxicants, as well as, environmental samples were tested by evaluating their effect on bacterial luminescence. This is the first step in the creation of a sensitive and simple operative tool that may be used in different environments.

Tracking transience: a method for dynamic monitoring of biological events in Arabidopsis thaliana biosensors

The activation and level of expression of an endogenous, stress-responsive biosensor (bioreporter) can be visualized in real-time and non-destructively using highly accessible equipment (fluorometer). Biosensor output can be linked to computer-controlled systems to enable feedback-based control of a greenhouse environment. Today's agriculture requires an ability to precisely and rapidly assess the physiological stress status of plants in order to optimize crop yield. Here we describe the implementation and utility of a detection system based on a simple fluorometer design for real-time, continuous, and non-destructive monitoring of a genetically engineered biosensor plant. We report the responses to heat stress of Arabidopsis thaliana plants expressing a Yellow Fluorescent Protein bioreporter under the control of the DREB2A temperature-sensing promoter. Use of this bioreporter provides the ability to identify transient and steady-state behavior of gene activation in response to stress, and serves as an interface for novel experimental protocols. Models identified through such experiments inform the development of computer-based feedback control systems for the greenhouse environment, based on in situ monitoring of mature plants. More broadly, the work here provides a basis for informing biologists and engineers about the kinetics of bioreporter constructs, and also about ways in which other fluorescent protein constructs could be integrated into automated control systems.

Silver, zinc oxide and titanium dioxide nanoparticle ecotoxicity to bioluminescent Pseudomonas putida in laboratory medium and artificial wastewater

Bacteria based ecotoxicology assessment of manufactured nanoparticles is largely restricted to Escherichia coli bioreporters in laboratory media. Here, toxicity effects of model OECD nanoparticles (Ag NM-300K, ZnO NM-110 and TiO2 NM-104) were assessed using the switch-off luminescent Pseudomonas putida BS566::luxCDABE bioreporter in Luria Bertani (LB) medium and artificial wastewater (AW). IC50 values ∼4 mg L(-1), 100 mg L(-1) and >200 mg L(-1) at 1 h were observed in LB for Ag NM-300K, ZnO NM-110 and TiO2 NM-104, respectively. Similar results were obtained in AW for Ag NM-300K (IC50∼5 mg L(-1)) and TiO2 NM-104 (IC50>200 mg L(-1)) whereas ZnO NM-110 was significantly higher (IC50>200 mg L(-1)). Lower ZnO NM-110 toxicity in AW compared to LB was associated with differences in agglomeration status and dissolution rate. This work demonstrates the importance of nanoecotoxicological studies in environmentally relevant matrices.

Organic acids enhance bioavailability of tetracycline in water to Escherichia coli for uptake and expression of antibiotic resistance

Tetracyclines are a large class of antimicrobials used most extensively in livestock feeding operations. A large portion of tetracyclines administered to livestock is excreted in manure and urine which is collected in waste lagoons. Subsequent land application of these wastes introduces tetracyclines into the soil environment, where they could exert selective pressure for the development of antibiotic resistance genes in bacteria. Tetracyclines form metal-complexes in natural waters, which could reduce their bioavailability for bacterial uptake. We hypothesized that many naturally-occurring organic acids could effectively compete with tetracyclines as ligands for metal cations, hence altering the bioavailability of tetracyclines to bacteria in a manner that could enhance the selective pressure. In this study, we investigated the influence of acetic acid, succinic acid, malonic acid, oxalic acid and citric acid on tetracycline uptake from water by Escherichia coli bioreporter construct containing a tetracycline resistance gene which induces the emission of green fluorescence when activated. The presence of the added organic acid ligands altered tetracycline speciation in a manner that enhanced tetracycline uptake by E. coli. Increased bacterial uptake of tetracycline and concomitant enhanced antibiotic resistance response were quantified, and shown to be positively related to the degree of organic acid ligand complexation of metal cations in the order of citric acid > oxalic acid > malonic acid > succinic acid > acetic acid. The magnitude of the bioresponse increased with increasing aqueous organic acid concentration. Apparent positive relation between intracellular tetracycline concentration and zwitterionic tetracycline species in aqueous solution indicates that (net) neutral tetracycline is the species which most readily enters E. coli cells. Understanding how naturally-occurring organic acid ligands affect tetracycline speciation in solution, and how speciation influences tetracycline uptake by bacteria, allows more accurate assessment of the selective pressure from trace levels of antibiotics in the environment on microbial communities for preserving and developing antibiotic resistance.

Evaluation of the leucine incorporation technique for detection of pollution-induced community tolerance to copper in a long-term agricultural field trial with urban waste fertilizers

Copper (Cu) is known to accumulate in agricultural soils receiving urban waste products as fertilizers. We here report the use of the leucine incorporation technique to determine pollution-induced community tolerance (Leu-PICT) to Cu in a long-term agricultural field trial. A significantly increased bacterial community tolerance to Cu was observed for soils amended with organic waste fertilizers and was positively correlated with total soil Cu. However, metal speciation and whole-cell bacterial biosensor analysis demonstrated that the observed PICT responses could be explained entirely by Cu speciation and bioavailability artifacts during Leu-PICT detection. Hence, the agricultural application of urban wastes (sewage sludge or composted municipal waste) simulating more than 100 years of use did not result in sufficient accumulation of Cu to select for Cu resistance. Our findings also have implications for previously published PICT field studies and demonstrate that stringent PICT detection criteria are needed for field identification of specific toxicants.

C60 reduces the bioavailability of mercury in aqueous solutions

The effects of C60 on mercury bioavailability and sorption were investigated at different C60 dosages, reaction times, and pH ranges using the merR::luxCDABE bioluminescent bioreporter Escherichia coli ARL1. The results demonstrated that the bioavailability of mercury (Hg(2+)) decreased with increasing C60 dosage. Approximately 30% of aqueous mercury became biologically unavailable 2h after interaction with C60 at a mass ratio of C60 to mercury as low as 0.01. However, this reduction in bioavailability plateaued at a mass ratio of C60 to mercury of 10 with a further increase in C60 concentrations resulting in only a 20% additional decrease in bioavailability. If this reduction in bioluminescence output is attributable to mercury sorption on C60, then each one log-order increase in C60 concentration resulted in a 0.86 log-order decrease in the mercury partitioning coefficient (Kd). This relationship implies the presence of high mercury-affinitive sites on C60. The length of reaction time was found to play a more important role than C60 dosage in reducing Hg(2+) bioavailability, suggesting an overall slow kinetics of the C60-Hg interactions. In addition, lowering the pH from 7.2 to 5.8 decreased mercury bioavailability due likely to the increase in mercury's association with C60. These results suggest that C60 may be useful in capturing soluble mercury and thus reducing mercury biotoxicity.

Continuous, real-time bioimaging of chemical bioavailability and toxicology using autonomously bioluminescent human cell lines

Bioluminescent imaging is an emerging biomedical surveillance strategy that uses external cameras to detect in vivo light generated in small animal models of human physiology or in vitro light generated in tissue culture or tissue scaffold mimics of human anatomy. The most widely utilized of reporters is the firefly luciferase (luc) gene; however, it generates light only upon addition of a chemical substrate, thus only generating intermittent single time point data snapshots. To overcome this disadvantage, we have demonstrated substrate-independent bioluminescent imaging using an optimized bacterial bioluminescence (lux) system. The lux reporter produces bioluminescence autonomously using components found naturally within the cell, thereby allowing imaging to occur continuously and in real-time over the lifetime of the host. We have validated this technology in human cells with demonstrated chemical toxicological profiling against exotoxin exposures at signal strengths comparable to existing luc systems (~1.33 × 10⁷ photons/second). As a proof-in-principle demonstration, we have engineered breast carcinoma cells to express bioluminescence for real-time screening of endocrine disrupting chemicals and validated detection of 17β-estradiol (EC₅₀ = ~ 10 pM). These and other applications of this new reporter technology will be discussed as potential new pathways towards improved models of target chemical bioavailability, toxicology, efficacy, and human safety.

Genetically modified whole-cell bioreporters for environmental assessment

Living whole-cell bioreporters serve as environmental biosentinels that survey their ecosystems for harmful pollutants and chemical toxicants, and in the process act as human and other higher animal proxies to pre-alert for unfavorable, damaging, or toxic conditions. Endowed with bioluminescent, fluorescent, or colorimetric signaling elements, bioreporters can provide a fast, easily measured link to chemical contaminant presence, bioavailability, and toxicity relative to a living system. Though well tested in the confines of the laboratory, real-world applications of bioreporters are limited. In this review, we will consider bioreporter technologies that have evolved from the laboratory towards true environmental applications, and discuss their merits as well as crucial advancements that still require adoption for more widespread utilization. Although the vast majority of environmental monitoring strategies rely upon bioreporters constructed from bacteria, we will also examine environmental biosensing through the use of less conventional eukaryotic-based bioreporters, whose chemical signaling capacity facilitates a more human-relevant link to toxicity and health-related consequences.

Coexpression of luxA and luxB genes of Vibrio fischeri in NIH3T3 mammalian cells and evaluation of its bioluminescence activities

Expression of bacterial luciferase enzyme (lux) in eukaryotic cells would provide a new bioreporter system for in vivo imaging and diagnostics technology. In spite of this, until now only a few efforts have been made to express bacterial luciferase enzyme in eukaryotic cells. We attempted to synthesize an expression construct of luxA and luxB genes from Vibrio fischeri. The luxA and luxB genes were cloned into the MCS of pTZ57R via the 5' kpnI, BamHI and BamHI, EcoRI restriction sites to generate pTZ57R/luxA and pTZ57R/luxB respectively, then newly synthesized constructs were cleaved with the same enzymes and respectively cloned into the pcDNA3.1(+) (Hyg) and pcDNA3.1(+) (Neo) expression vectors to create pcDNA3.1(+) (Hyg)/luxA and pcDNA3.1(+) (neo)/luxB. Recombinant constructs were cotransfected to the NIH3T3 cell line. Gene expression was confirmed by reverse transcription-polymerase chain reaction, sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting; in addition, bioluminescence characteristics of transfected NIH3T3 cell lines were evaluated by decanal supplement. In conclusion, in the current research, separate vector systems were constructed, which are composed of bacterial luciferase genes (luxA and luxB) that accordingly have not already been reported. These results hold promise toward the potential development of an autonomous light-generating lux reporter system in eukaryotic cells.