Effect of cadmium(II), chromium(VI), and arsenic(V) on long-term viability- and growth-inhibition assays using Vibrio fischeri marine bacteria

Effects of New Btk-Based Formulations BLB1 and Lip on Aquatic Non-Target Organisms

Integrated pest management based on the use of biopesticides is largely applied. Experimental bioassays are critical to assess biopesticide biosafety at the ecotoxicological level. In this study, we investigated the effects of the new Bacillus thuringiensis subsp. kurstaki (Btk)-formulated-based biopesticides BLB1 and Lip, efficiently tested in field assays (IPM-4-CITRUS EC project no. 734921) on two aquatic non-target organisms, precisely the water flea Daphnia magna and the bioluminescent bacteria Aliivibrio fischeri. Acute toxicity studies, carried out in a comparative manner with Delfin® as the reference bioproduct and the lactose-based Blank formulation, show that no significant toxicity was observed up to 1 g/L. Our results indicated that BLB1- and Lip-formulated new bioproducts are far less toxic than the Delfin® reference bioproduct.

Long-term toxicity assessment of antibiotics against Vibrio fischeri: Test method optimization and mixture toxicity prediction

The current luminescent bacteria test for acute toxicity with short contact time was invalid for antibiotics, and the non-uniformed contact times reported in the literature for long-term toxicity assessment led to incomparable results. Herein, a representative long-term toxicity assessment method was established which unified the contact time of antibiotics and Vibrio fischeri within the bioluminescence increasing period (i.e. 10-100% maximum luminescence) of control samples. The effects of excitation and detoxification of antibiotics such as β-lactams were discovered. Half maximal inhibitory concentration (IC50) of toxic antibiotics (0.00069-0.061 mmol/L) obtained by this method was 2-3 orders of magnitude lower than acute test, quantifying the underestimated toxicity. As antibiotics exist in natural water as mixtures, an equivalent concentration addition (ECA) model was built to predict mixture toxicity based on physical mechanism rather than mathematical method, which showed great fitting results (R2 = 0.94). Furthermore, interaction among antibiotics was investigated. Antibiotics acting during bacterial breeding period had strong synergistic inhibition (IC50 relative deviation from 0.1 to 0.6) such as macrolides and quinolones. Some antibiotics produced increasing synergistic inhibition during concentration accumulation, such as macrolides. The discharge of antibiotics with severe long-term toxicity and strong synergistic inhibition effect should be seriously restricted.

Identification and Genome Analysis of an Arsenic-Metabolizing Strain of Citrobacter youngae IITK SM2 in Middle Indo-Gangetic Plain Groundwater

Whole-genome sequencing (WGS) data of a bacterial strain IITK SM2 isolated from an aquifer located in the middle Indo-Gangetic plain is reported here, along with its physiological, morphological, biochemical, and redox-transformation characteristics in the presence of dissolved arsenic (As). The aquifer exhibits oxidizing conditions relative to As speciation. Analyses based on 16S rRNA and recN sequences indicate that IITK SM2 was clustered with C. youngae NCTC 13708T and C. pasteuri NCTC UMH17T. However, WGS analyses using the digital DNA-DNA hybridization and Rapid Annotations using Subsystems Technology suggest that IITK SM2 belongs to a strain of C. youngae. This strain can effectively reduce As(V) to As(III) but cannot oxidize As(III) to As(V). It exhibited high resistance to As(V) [32,000 mg L-1] and As(III) [1,100 mg L-1], along with certain other heavy metals typically found in contaminated groundwater. WGS analysis also indicates the presence of As-metabolizing genes such as arsC, arsB, arsA, arsD, arsR, and arsH in this strain. Although these genes have been identified in several As(V)-reducers, the clustering of these genes in the forms of arsACBADR, arsCBRH, and an independent arsC gene has not been observed in any other Citrobacter species or other selected As(V)-reducing strains of Enterobacteriaceae family. Moreover, there were differences in the number of genes corresponding to membrane transporters, virulence and defense, motility, protein metabolism, phages, prophages, and transposable elements in IITK SM2 when compared to other strains. This genomic dataset will facilitate subsequent molecular and biochemical analyses of strain IITK SM2 to identify the reasons for high arsenic resistance in Citrobacter youngae and understand its role in As mobilization in middle Indo-Gangetic plain aquifers.

Effects of crude oil and aromatic compounds on growth and bioluminescence of Vibrio campbellii FS5

Fifteen native luminescent bacteria were isolated from the Gulf of Thailand, and their sensitivity for the detection of toxicity of crude oil and its aromatic components was investigated. Of these isolates, Vibrio campbellii strain FS5 was one of the two most highly inhibited bacteria at all crude oil concentrations. This bacterium showed a decrease in luminescence intensity of between 10.7 and 80.2% after a 15-min exposure to 0.0001-10 mg/L of crude oil. The degree of bioluminescence inhibition increased with increasing concentrations of crude oil. The presence of crude oil at all concentrations had negative effects on the log bioluminescence per log number of viable cells after 15- to 105-min exposure. About 10 to 100 times, lower half maximal effective concentration (EC₅₀) values were observed for polycyclic aromatic hydrocarbons (PAHs) than those for benzene, toluene, ethylbenzene, and xylene (BTEX). In the presence of each individual BTEX and PAH, the bioluminescence inhibition increased with increasing exposure time (1-32 h). This indigenous bacterium can be used as a simple and general indicator of oil contamination and its impact on coastal waters as well as for assessing potential toxicity during oil bioremediation.

Toxicity assessment of total petroleum hydrocarbons in aquatic environments using the bioluminescent bacterium Aliivibrio fischeri

Toxicity monitoring of environmental pollutants especially petroleum hydrocarbons as priority pollutants is an important environmental issue. This study addresses a rapid, sensitive and cost effective method for the detection of total petroleum hydrocarbons (TPHs) using Aliivibrio fischeri bioluminescence inhibition bioassay. At the first step, the optimum conditions including time, pH and temperature for growth of A. fischeri were determined. Then, two methods were used to evaluate the toxicity of petroleum compounds. In the first method, short-term (15 min) and long-term (16 h) toxicity assays were performed. In the second method luminescence kinetics of A. fischeri was investigated during 24 h. The results demonstrated the most appropriate time for the bacterial growth occurred 16 h after inoculation and optimum temperature and pH were found 25 °C and 7, respectively. Short-term and long-term toxicity did not indicate any toxicity for various concentrations of TPHs (30, 50, 110, 160, 220 mg/L). Considering the luminescence kinetics of A. fischeri the long-term assay was introduced as 6 h. The half maximal effective concentration (EC₅₀) was achieved 1.77 mg/L of TPHs. It is concluded that the luminescence kinetics of A. fischeri can be a valuable approach for assessing toxicity of TPHs in aquatic environments.

Bacterial Toxicity Testing: Modification and Evaluation of the Luminescent Bacteria Test and the Respiration Inhibition Test

The activated sludge respiration inhibition test and the luminescent bacteria test with Vibrio fischeri are important bacterial test systems for evaluation of the toxicity of chemical compounds. These test systems were further optimized to result in better handling, reliability and sensitivity. Concerning the Vibrio fischeri test, media components such as yeast extract and bivalent cation concentrations like Ca2+ and Mg2+ were optimized. The cultivation, storage conditions and reactivation process of the stored bacteria were also improved, which enabled simpler handling and led to good reproducibility. Additionally, the respiration inhibition test with a prolonged incubation time was further analyzed using different chlorinated phenols as reference compounds. It could be stated that a longer incubation period significantly improved the sensitivity of the test system.

Self-Emulsified Nanoemulsion for Vaginal Administration: In Vitro Study of Effect on Lactobacillus acidophilus

Self-emulsified nanoemulsions (SENs), one of the promising lipid-based drug delivery systems may be used to deliver drugs through vaginal route. Vaginal cavity remains healthy because of the defensive action by its microflora against the pathogenic infections, and any disturbance to this microflora by the delivery systems gives invitation to the infections. In the present study, the growth inhibition and cytotoxic effects of two SENs and their components on L. acidophilus were evaluated. The two SENs showed inhibitory effects on the growth of L. acidophilus in a concentration-dependent manner when tested at the concentration range of 0.1-5.0%. The SEN composed of medium chain mono/di-glyceride had greater inhibitory effect than the one composed of long chain monoglyceride. The study on the effect by the individual lipids with the surfactant Kolliphor® RH40 further confirmed that the growth inhibitory and cytotoxic effects were in the order of Capmul® MCM > Maisine® CC > Miglyol® 810 > Kolliphor® RH40. Both OD₆₀₀ and CFU counting were used to measure the viability of the culture. The results from the two methods were in good correlation except when there was no growth, suggesting OD₆₀₀ can be used when there is no complete growth inhibition.

Probing the single and combined toxicity of PFOS and Cr(VI) to soil bacteria and the interaction mechanisms

Many research focused on the removal of perfluorooctane sulfonic acid (PFOS) and hexavalent chromium (Cr(VI)) in some industrial wastewater (e.g. electroplating wastewater), but few research reported the combined toxicity of PFOS and Cr(VI) to soil bacteria. Therefore, the toxicity and mechanisms of the combined PFOS and Cr(VI) to bacteria (with Bacillus subtilis as a model) are explored. The results show that the combined PFOS and Cr(VI) exhibits much higher toxicity to the bacteria than that of Cr(VI) alone. The growth profile of Bacillus subtilis exposed by the combined pollution decreased by 18% and 56%, respectively, compared with that of single Cr(VI) and the control, indicating the combined toxicity to Bacillus subtilis is synergistic. Moreover, the changes of EPSs in Bacillus subtilis, such as decreased potential, increased extracellular polysaccharides, decreased extracellular proteins and irregular morphology, also confirmed that the combined PFOS and Cr(VI) caused greater toxicity. The increase of intracellular ROS and permeability of dye 4', 6-diamidino-2-phenylindoledihydrochloride (DAPI) suggest that oxidative damage and increased membrane permeability are the main mechanisms of toxicity induced by the combined PFOS and Cr(VI). This work could provide useful information for the risk assessment of co-exposure to PFOS and heavy metals in the natural environment.

Microbial toxicity of gallium- and indium-based oxide and arsenide nanoparticles

III-V semiconductor materials such as gallium arsenide (GaAs) and indium arsenide (InAs) are increasingly used in the fabrication of electronic devices. There is a growing concern about the potential release of these materials into the environment leading to effects on public and environmental health. The waste effluents from the chemical mechanical planarization process could impact microorganisms in biological wastewater treatment systems. Currently, there is only limited information about the inhibition of gallium- and indium-based nanoparticles (NPs) on microorganisms. This study evaluated the acute toxicity of GaAs, InAs, gallium oxide (Ga₂O₃), and indium oxide (In₂O₃) particulates using two microbial inhibition assays targeting methanogenic archaea and the marine bacterium, Aliivibrio fischeri. GaAs and InAs NPs were acutely toxic towards these microorganisms; Ga₂O₃ and In₂O₃ NPs were not. The toxic effect was mainly due to the release of soluble arsenic species and it increased with decreasing particle size and with increasing time due to the progressive corrosion of the NPs in the aqueous bioassay medium. Collectively, the results indicate that the toxicity exerted by the arsenide NPs under environmental conditions will vary depending on intrinsic properties of the material such as particle size as well as on the dissolution time and aqueous chemistry.

Towards a multi-bioassay-based index for toxicity assessment of fluvial waters

Despite their proven reliability for revealing 'acceptable' degrees of toxicity in waste- and reclaimed waters, bioassays are rarely used to assess the toxicity of hazardous contaminants present in natural waters. In this study, we used organisms from different trophic levels to assess the toxicity of water samples collected from four different South Korean rivers. The main objective was to develop a multi-descriptor index of toxicity for undiluted river water. The responses of six test organisms (Aliivibrio fischeri, Pseudokirchneriella subcapitata, Heterocypris incongruens, Moina macrocopa, Danio rerio and Lemna minor) after laboratory exposure to water samples were considered for this index, as well as the frequency of teratologies in diatom assemblages. Each individual test was attributed a toxicity class and score (three levels; no toxicity = 0, low toxicity = 1, confirmed toxicity = 2) based on the organism's response after exposure and a total score was calculated. The proposed index also considers the number of test organisms that received the highest toxicity score (value = 2). An overall toxicity category was then attributed to the water sample based on those two metrics: A = no toxicity, B = slight toxicity, C = moderate toxicity; D = toxicity and E = high toxicity. The susceptibility of the test organisms varied greatly and the sensitivity of their response also differed among bioassays. The combined responses of organisms from different trophic levels and with different life strategies provided multi-level diagnostic information about the intensity and the nature of contamination.

A swinging seesaw as a novel model mechanism for time-dependent hormesis under dose-dependent stimulatory and inhibitory effects: A case study on the toxicity of antibacterial chemicals to Aliivibrio fischeri

Hormesis occurs frequently in broadly ranging biological areas (e.g. plant biology, microbiology, biogerontology), toxicology, pharmacology and medicine. While numerous mechanisms (e.g. receptor and pathway mediated pathway responses) account for stimulatory and inhibitory features of hormetic dose responses, the vast majority emphasizes the inclusion of many doses but only one timepoint or use of a single optimized dose that is assessed over a broad range of timepoints. In this paper, a toxicity study was designed using a large number of properly spaced doses with responses determined over a large number of timepoints, which could help us reveal the underlying mechanism of hormesis. We present the results of a dose-time-response study on hormesis using five antibacterial chemicals on the bioluminescence of Aliivibrio fischeri, measuring expression of protein mRNA based on quorum sensing, simulating bioluminescent reaction and analyzing toxic actions of test chemicals. The findings show dose-time-dependent responses conforming to the hormetic dose-response model, while revealing unique response dynamics between agent induced stimulatory and inhibitory effects within bacterial growth phase dynamics. These dynamic dose-time features reveal a type of biological seesaw model that integrates stimulatory and inhibitory responses within unique growth phase, dose and time features, which has faultlessly explained the time-dependent hormetic phenomenon induced by five antibacterial chemicals (characterized by low-dose stimulation and high-dose inhibition). This study offers advances in understanding cellular dynamics, the biological integration of diverse and opposing responses and their role in evolutionary adaptive strategies to chemicals, which can provide new insight into the mechanistic investigation of hormesis.

Mechanistic explanation of time-dependent cross-phenomenon based on quorum sensing: A case study of the mixture of sulfonamide and quorum sensing inhibitor to bioluminescence of Aliivibrio fischeri

Cross-phenomenon in which the concentration-response curve (CRC) for a mixture crosses the CRC for the reference model has been identified in many studies, expressed as a heterogeneous pattern of joint toxic action. However, a mechanistic explanation of the cross-phenomenon has thus far been extremely insufficient. In this study, a time-dependent cross-phenomenon was observed, in which the cross-concentration range between the CRC for the mixture of sulfamethoxypyridazine (SMP) and (Z-)-4-Bromo-5-(bromomethylene)-2(5H)-furanone (C30) to the bioluminescence of Aliivibrio fischeri (A. fischeri) and the CRC for independent action model with 95% confidence bands varied from low-concentration to higher-concentration regions in a timely manner expressed the joint toxic action of the mixture changing with an increase of both concentration and time. Through investigating the time-dependent hormetic effects of SMP and C30 (by measuring the expression of protein mRNA, simulating the bioluminescent reaction and analyzing the toxic action), the underlying mechanism was as follows: SMP and C30 acted on the quorum sensing (QS) system of A. fischeri, which induced low-concentration stimulatory effects and high-concentration inhibitory effects; in the low-concentration region, the stimulatory effects of SMP and C30 made the mixture produce a synergistic stimulation on the bioluminescence; thus, the joint toxic action exhibited antagonism. In the high-concentration region, the inhibitory effects of SMP and C30 in the mixture caused a double block in the loop circuit of the QS system; thus, the joint toxic action exhibited synergism. With the increase of time, these stimulatory and inhibitory effects of SMP and C30 were changed by the variation of the QS system at different growth phases, resulting in the time-dependent cross-phenomenon. This study proposes an induced mechanism for time-dependent cross-phenomenon based on QS, which may provide new insight into the mechanistic investigation of time-dependent cross-phenomenon, benefitting the environmental risk assessment of mixtures.

Effects of Cr(III) and Cr(VI) on nitrification inhibition as determined by SOUR, function-specific gene expression and 16S rRNA sequence analysis of wastewater nitrifying enrichments

The effect of Cr(III) and Cr(VI) on nitrification was examined with samples from nitrifying enrichment cultures using three different approaches: by measuring substrate (ammonia) specific oxygen uptake rates (SOUR), by using RT-qPCR to quantify the transcripts of functional genes involved in nitrification, and by analysis of 16S rRNA sequences to determine changes in structure and activity of the microbial communities. The nitrifying bioreactor was operated as a continuous reactor with a 24 h hydraulic retention time. The samples were exposed in batch vessels to Cr(III) (10-300 mg/L) and Cr(VI) (1-30 mg/L) for a period of 12 h. There was considerable decrease in SOUR with increasing dosages for both Cr(III) and Cr(VI), however Cr(VI) was more inhibitory than Cr(III). Based on the RT-qPCR data, there was reduction in the transcript levels of amoA and hao for increasing Cr(III) dosage, which corresponded well with the ammonia oxidation activity measured via SOUR. For Cr(VI) exposure, there was comparatively little reduction in amoA expression while hao expression decreased for 1-3 mg/L Cr(VI) and increased at 30 mg/L Cr(VI). While Nitrosomonas spp. were the dominant bacteria in the bioreactor, based on 16S rRNA sequencing, there was a considerable reduction in Nitrosomonas activity upon exposure to 300 mg/L Cr(III). In contrast, a relatively small reduction in activity was observed at 30 mg/L Cr(VI) loading. Our data that suggest that both Cr(III) and Cr(VI) were inhibitory to nitrification at concentrations near the high end of industrial effluent concentrations.

Time-dependent hormesis of chemical mixtures: A case study on sulfa antibiotics and a quorum-sensing inhibitor of Vibrio fischeri

Sulfa antibiotics (SAs) and quorum-sensing inhibitor (QSI) may pose potential ecological risks because mixed using of them has been proposed to inhibit bacteria from generating antibiotic resistance. This study investigated the time-dependent hormesis of single and binary mixtures of QSI and SAs of Vibrio fischeri (V. fischeri) for 0-24 h. Although the low-dose SAs stimulated the expression of LuxR protein, the high-dose SAs could inhibit bacteria growth by competitively binding to dihydropteroate synthase. Moreover, AinR protein was bound to Benzofuran-3(2H)-one (B3O) with low concentration, thus the N-octanoyl homoserine lactone signal molecules (C8) has chance to bind to LuxR protein to promote light emission. The hormesis effect induced by the mixtures could be deduced that SAs promoted the expression of LuxR protein and B3O increases the chance of C8 binding to LuxR. Our findings facilitate new insight into the mechanistic study of hormesis and ecological risks of the chemical mixtures.

A new P. putida instrumental toxicity bioassay

Here, we present a new toxicity bioassay (CO2-TOX), able to detect toxic or inhibitory compounds in water samples, based on the quantification of Pseudomonas putida KT2440 CO2 production. The metabolically produced CO2 was measured continuously and directly in the liquid assay media, with a potentiometric gas electrode. The optimization studies were performed using as a model toxicant 3,5-DCP (3,5-dichlorophenol); later, heavy metals (Pb(2+), Cu(2+), or Zn(2+)) and a metalloid (As(5+)) were assayed. The response to toxics was evident after 15 min of incubation and at relatively low concentrations (e.g., 1.1 mg/L of 3,5-DCP), showing that the CO2-TOX bioassay is fast and sensitive. The EC50 values obtained were 4.93, 0.12, 6.05, 32.17, and 37.81 mg/L for 3,5-DCP, Cu(2+), Zn(2+), As(5+), and Pb(2+), respectively, at neutral pH. Additionally, the effect of the pH of the sample and the use of lyophilized bacteria were also analyzed showing that the bioassay can be implemented in different conditions. Moreover, highly turbid samples and samples with very low oxygen levels were measured successfully with the new instrumental bioassay described here. Finally, simulated samples containing 3,5-DCP or a heavy metal mixture were tested using the proposed bioassay and a standard ISO bioassay, showing that our test is more sensible to the phenol but less sensible to the metal mixtures. Therefore, we propose CO2-TOX as a rapid, sensitive, low-cost, and robust instrumental bioassay that could perform as an industrial wastewater-process monitor among other applications.

Flue-gas-influenced heavy metal bioaccumulation by the indigenous microalgae Desmodesmus communis LUCC 002

Desmodesmus communis LUCC 002 was cultivated using flue gas originating from a coal-fired power plant as a carbon dioxide (CO2) source. The flue gas contains various heavy metals. For investigating the fate of flue-gas-introduced metals on the cultivation system, bioaccumulation was measured in the microalgal biomass and milieu. The accumulated biomass was found to contain eight heavy metals: arsenic, chromium, barium, lead, selenium, silver, cadmium, and mercury. High heavy metal accumulations were also found in the control group of algae grown without the addition of flue gas at the same location. Further testing revealed that some of the heavy metals originated from well water used in the cultivation. The flue-gas-influenced bioaccumulation pattern of different heavy metals was observed. The responses of individual heavy metals and the influence of well water microbial flora on the algal growth were investigated, this study showed that hormesis was developed by the D. communis LUCC 002.

Response of growth and superoxide dismutase to enhanced arsenic in two Bacillus species

Species differences in inorganic arsenic tolerance were investigated by comparing the responses of Bacillus subtilis (B. subtilis) and Bacillus thuringiensis (B. thuringiensis) to elevated concentrations of As(III) and As(V). The cell densities in treatments were always lower during the experiment compared to controls, with the exception of exposure to 1.0 mg As(V) l(-1) on the first day. It was also found that relative growth rate (RGR) of B. thuringiensis was lower than that of B. subtilis. Furthermore, RGR of each Bacillus species was negative correlation with toxicity of inorganic arsenic. However, total cell number still increased in each treatment according to cell density and RGR assays. Superoxide dismutase (SOD) activity of both Bacillus species was promoted by As(III) and As(V), especially under high arsenic concentration condition. In addition, SOD activity of B. thuringiensis was higher than that of B. subtilis during the same exposure time. In lipid peroxidation assay, thiobarbituric acid-reactive substances (TBARS) content of each Bacillus species had a significant increase with increment of arsenic concentration. Moreover, significant difference was observed between the two Bacillus species under high arsenic concentration. TBARS content of B. thuringiensis was higher than that of B. subtilis, indicating that effect of arsenic on cell membranes of B. thuringiensis was much more than that of B. subtilis. These results suggest that the two Bacillus species could adapt and live in high arsenic aquifers, although their growth and cell membranes were affected by As treatment in a way.

Effects of binary mixtures of inducers (toluene analogs) and of metals on bioluminescence induction of a recombinant bioreporter strain

This paper investigated the effects of binary mixtures of bioluminescence inducers (toluene, xylene isomers, m-toluate) and of metals (Cu, Cd, As(III), As(V), and Cr) on bioluminescence activity of recombinant (Pm-lux) strain KG1206. Different responses and sensitivities were observed depending on the types and concentrations of mixtures of inducers or metals. In the case of inducer mixtures, antagonistic and synergistic modes of action were observed, whereas metal mixtures showed all three modes of action. Antagonistic mode of action was most common for mixtures of indirect inducers, which showed bioluminescence ranging from 29% to 62% of theoretically expected effects (P(E)). On the other hand, synergistic mode of action was observed for mixtures of direct and indirect inducers, which showed bioluminescence between 141% and 243% of P(E). In the case of binary metal mixtures, bioluminescence activities were ranged from 62% to 75% and 113% to 164% of P(E) for antagonistic and synergistic modes of action, respectively (p-values 0.0001-0.038). Therefore, mixture effects could not be generalized since they were dependent on both the types and concentrations of chemicals, suggesting that biomonitoring may constitute a better strategy by investigating types and concentrations of mixture pollutants at contaminated sites.

Ecotoxicity and environmental risk assessment of pharmaceuticals and personal care products in aquatic environments and wastewater treatment plants

A wide range of pharmaceuticals and personal care products (PPCPs) are present in the environment, and many of their adverse effects are unknown. The environmental risk assessment of 26 PPCPs of relevant consumption and occurrence in the aquatic environment in Spain was accomplished in this research. Based on the ecotoxicity values obtained by bioluminescence and respirometry assays and by predictions using the US EPA ecological structure-activity relationship (ECOSAR™), the compounds were classified following the Globally Harmonized System of Classification and Labelling of Chemicals. According to the criteria of the European Medicines Agency, the real risk of impact of these compounds in wastewater treatment plants (WWTPs) and in the aquatic environment was predicted. In at least two ecotoxicity tests, 65.4 % of the PPCPs under study showed high toxicity or were harmful to aquatic organisms. The global order of the species' sensitivity to the PPCPs considered was as follows: Vibrio fischeri (5 min) > Vibrio fischeri (15 min) > algae > crustaceans > fish > biomass of WWTP. Acetaminophen, ciprofloxacin, clarithromycin, clofibrate, ibuprofen, omeprazole, triclosan, parabens and 1,4-benzoquinone showed some type of risk for the aquatic environments and/or for the activated sludge of WWTPs. Development of acute and chronic ecotoxicity data, the determination of predicted and measured environmental concentrations of PPCPs, the inclusion of metabolites and transformation products and the evaluation of mixtures of these compounds will allow further improvements of the results of the ERAs and, finally, to efficiently identify the compounds that could affect the environment.

Growth, bioluminescence and shoal behavior hormetic responses to inorganic and/or organic chemicals: a review

A biphasic dose response, termed hormesis, is characterized by beneficial effects of a chemical at a low dose and harmful effects at a high dose. This biphasic dose response phenomenon has the potential to strongly alter toxicology in a broad range. The present review focuses on the progress of research into hormetic responses in terms of growth (in plants, birds, algae and humans), bioluminescence, and shoal behavior as end points. The paper describes how both inorganic and organic chemicals at a low dose show stimulatory responses while at higher doses are inhibitory. The article highlights how factors such as symbiosis, density-dependent factors, time, and contrasting environmental factors (availability of nutrients, temperature, light, etc.) affect both the range and amplitude of hormetic responses. Furthermore, the possible underlying mechanisms are also discussed and we suggest that, for every end point, different hormetic mechanisms may exist. The occurrences of varying interacting receptor systems or receptor systems affecting the assessment of hormesis for each endpoint are discussed. The present review suggests that a hormetic model should be adopted for toxicological evaluations instead of the older threshold and linear non-threshold models.

Mar Piccolo of Taranto: Vibrio biodiversity in ecotoxicology approach

Microorganisms play an indispensable role in the ecological functioning of marine environment. Some species are sensitive while others are insensitive for a specific pollutant. The aim of this work is a preliminary study of the quantitative and qualitative distribution of cultivable vibrios in sediments and water samples characterized by different toxicity levels. For 1 year, in three suitably selected sampling stations of Mar Piccolo in Taranto (Ionian Sea, Italy), we have evaluated the toxicity level by Microtox® system, vibrios, total, and fecal coliform densities. The results of the Microtox® tests showed sediments characterized by an elevated level of toxicity, while the interstitial water of the same sites always showed biostimulatory phenomenon. The quantitative results show that vibrios and coliforms are more abundant in water than in sediment samples. The most often isolated strains were: Vibrio alginolyticus, Vibrio mediterranei, Vibrio metschinkovii, and Vibrio splendidus II. This work is the first example of study on the distribution of Vibrio species related to toxicity evaluation conducted by the Microtox® bioassay. The results show the different distribution of Vibrionaceae in two environmental matrices analyzed and characterized by different levels of toxicity.

Reduction of clarithromycin and sulfamethoxazole-resistant Enterococcus by pilot-scale solar-driven Fenton oxidation

The presence of pathogenic antibiotic-resistant bacteria in aquatic environments has become a health threat in the last few years. Their presence has increased due to the presence of antibiotics in wastewater effluents, which are not efficiently removed by conventional wastewater treatments. As a result there is a need to study the possible ways of removal of the mixtures of antibiotics present in wastewater effluents and the antibiotic-resistant bacteria, which may also spread the antibiotic resistance genes to other bacterial populations. In this study the degradation of a mixture of antibiotics i.e. sulfamethoxazole and clarithromycin, the disinfection of total enterococci and the removal of those resistant to: a) sulfamethoxazole, b) clarithromycin and c) to both antibiotics have been examined, along with the toxicity of the whole effluent mixture after treatment to the luminescent aquatic bacterium Vibrio fischeri. Solar Fenton treatment (natural solar driven oxidation) using Fenton reagent doses of 50 mg L(-1) of hydrogen peroxide and 5 mg L(-1) of Fe(3+) in a pilot-scale compound parabolic collector plant was used to examine the disinfection and antibiotic resistance removal efficiency in different aqueous matrices, namely distilled water, simulated and real wastewater effluents. There was a faster complete removal of enterococci and of antibiotics in all aqueous matrices by applying solar Fenton when compared to photolytic treatment of the matrices. Sulfamethoxazole was more efficiently degraded than clarithromycin in all three aqueous matrices (95% removal of sulfamethoxazole and 70% removal of clarithromycin in real wastewater). The antibiotic resistance of enterococci towards both antibiotics exhibited a 5-log reduction with solar Fenton in real wastewater effluent. Also after solar Fenton treatment, there were 10 times more antibiotic-resistant enterococci in the presence of sulfamethoxazole than in the presence of clarithromycin. Finally, the toxicity of the treated wastewater to V. fischeri remained very low throughout the treatment time.

Evaluation of the ecotoxicity of pollutants with bioluminescent microorganisms

This chapter deals with the use of bioluminescent microorganisms in environmental monitoring, particularly in the assessment of the ecotoxicity of pollutants. Toxicity bioassays based on bioluminescent microorganisms are an interesting complement to classical toxicity assays, providing easiness of use, rapid response, mass production, and cost effectiveness. A description of the characteristics and main environmental applications in ecotoxicity testing of naturally bioluminescent microorganisms, covering bacteria and eukaryotes such as fungi and dinoglagellates, is reported in this chapter. The main features and applications of a wide variety of recombinant bioluminescent microorganisms, both prokaryotic and eukaryotic, are also summarized and critically considered. Quantitative structure-activity relationship models and hormesis are two important concepts in ecotoxicology; bioluminescent microorganisms have played a pivotal role in their development. As pollutants usually occur in complex mixtures in the environment, the use of both natural and recombinant bioluminescent microorganisms to assess mixture toxicity has been discussed. The main information has been summarized in tables, allowing quick consultation of the variety of luminescent organisms, bioluminescence gene systems, commercially available bioluminescent tests, environmental applications, and relevant references.

The differential stress response of adapted chromite mine isolates Bacillus subtilis and Escherichia coli and its impact on bioremediation potential

In the current study, indigenous bacterial isolates Bacillus subtilis VITSUKMW1 and Escherichia coli VITSUKMW3 from a chromite mine were adapted to 100 mg L(-1) of Cr(VI). The phase contrast and scanning electron microscopic images showed increase in the length of adapted E. coli cells and chain formation in case of adapted B. subtilis. The presence of chromium on the surface of the bacteria was confirmed by energy dispersive X-ray spectroscopy (EDX), which was also supported by the conspicuous Cr-O peaks in FTIR spectra. The transmission electron microscopic (TEM) images of adapted E. coli and B. subtilis showed the presence of intact cells with Cr accumulated inside the bacteria. The TEM-EDX confirmed the internalization of Cr(VI) in the adapted cells. The specific growth rate and Cr(VI) reduction capacity was significantly higher in adapted B. subtilis compared to that of adapted E. coli. To study the possible role of Cr(VI) toxicity affecting the Cr(VI) reduction capacity, the definite assays for the released reactive oxygen species (ROS) and ROS scavenging enzymes (SOD and GSH) were carried out. The decreased ROS production as well as SOD and GSH release observed in adapted B. subtilis compared to the adapted E. coli corroborated well with its higher specific growth rate and increased Cr(VI) reduction capacity.

The interactions of Vibrio vulnificus and the oyster Crassostrea virginica

The human bacterial pathogen, Vibrio vulnificus, is found in brackish waters and is concentrated by filter-feeding molluscan shellfish, especially oysters, which inhabit those waters. Ingestion of raw or undercooked oysters containing virulent strains of V. vulnificus can result in rapid septicemia and death in 50 % of victims. This review summarizes the current knowledge of the environmental interactions between these two organisms, including the effects of salinity and temperature on colonization, uptake, and depuration rates of various phenotypes and genotypes of the bacterium, and host-microbe immunological interactions.

Cadmium-Induced Pathologies: Where Is the Oxidative Balance Lost (or Not)?

Over the years, anthropogenic factors have led to cadmium (Cd) accumulation in the environment causing various health problems in humans. Although Cd is not a Fenton-like metal, it induces oxidative stress in various animal models via indirect mechanisms. The degree of Cd-induced oxidative stress depends on the dose, duration and frequency of Cd exposure. Also the presence or absence of serum in experimental conditions, type of cells and their antioxidant capacity, as well as the speciation of Cd are important determinants. At the cellular level, the Cd-induced oxidative stress either leads to oxidative damage or activates signal transduction pathways to initiate defence responses. This balance is important on how different organ systems respond to Cd stress and ultimately define the pathological outcome. In this review, we highlight the Cd-induced oxidant/antioxidant status as well as the damage versus signalling scenario in relation to Cd toxicity. Emphasis is addressed to Cd-induced pathologies of major target organs, including a section on cell proliferation and carcinogenesis. Furthermore, attention is paid to Cd-induced oxidative stress in undifferentiated stem cells, which can provide information for future therapies in preventing Cd-induced pathologies.

Evaluation of an automated luminescent bacteria assay for in situ aquatic toxicity determination

A new system for monitoring toxicity TOXcontrol® (MicroLAN BV, The Netherlands) has been used to assess the toxicity of a selection of priority or emergent compounds in the laboratory. In this study, inhibition curves and EC50 - Effective Concentration causing 50% inhibition - of selected compounds (including pesticides, pharmaceuticals, surfactants and metals commonly detected in surface or drinking waters) were determined. This new technology is based on the measurement of Vibrio fischeri bioluminescence inhibition (ISO 11348). The main advantage of this equipment, compared to other laboratory assays, is the fully automation of the procedure. The instrument can be operated online in a simple, rapid and reproducible way. The variability of the results obtained with the TOXcontrol® biomonitoring system has been studied. A comparison with standardised technology based in V. fischeri (Microtox®) and additional test with Daphnia magna for selected organic compounds is presented. The results show that the methodology based on the TOXcontrol® system being validated is accurate and reproducible enough enabling this system to be used as an on-line automatic alert system to detect abnormal concentrations of toxic compounds.

Model of hormesis and its toxicity mechanism based on quorum sensing: a case study on the toxicity of sulfonamides to Photobacterium phosphoreum

During the past two decades, the phenomenon of hormesis has gained increasing recognition in environmental and toxicological communities. However, the mechanistic understanding of hormesis, to date, is extremely limited. Herein is proposed a novel parametric model with a mechanistic basis and two model-based parameters for hormesis that was successfully applied to the hormetic dose-response observed in the chronic toxicity of sulfonamides on Photobacterium phosphoreum. On the basis of the methods of molecular docking and quantitative structure-activity relationships (QSARs), we proposed a mechanistic hypothesis for hormesis that introduces for the first time the concept of quorum sensing in toxicological studies and explains the mechanism at the level of the receptors. The mechanistic hypothesis stated that (1) specific target binding like interaction with LuxR may contribute to transcriptional activation leading to enhanced luciferase activity at low dose exposure of sulfonamides, and (2) as the dose of sulfonamides increases, more sulfonamides competitively bind to dihydropteroate synthase, which inhibit the biosynthesis of folic acid and thus provoke toxicity. This mechanistic hypothesis, which explains both the dose-dependent and time-dependent features of hormesis, could give new insight into the mechanistic study of hormesis.

Optimal conditions for stability of photoemission and freeze drying of two luminescent bacteria for use in a biosensor

Bioluminescent bacteria have been used for many years for biotoxicological analysis. One of the main concerns with this microorganism is the low experimental repeatability when subjected to external factors. The aim of the present study was to obtain accurate, sensitive, and repeatable measurements with stable signals (during the detection and over days) for application in a water-analysis device for the detection of pollutants. Growth conditions were tested and optimized. An optimal freeze-drying procedure for the constitutive bioluminescent bacteria Vibrio fischeri and Photobacterium phosphoreum was developed. The luminescence stability after rehydration was also investigated. Freeze drying was found to be a critical process in survival and signal stability of luminescent bacteria; for this reason, different suspension fluids and various bacterial pellet/suspension fluid ratios (g/ml) were evaluated. The toxicity of heavy metals and organic compounds in water was determined to investigate the applicability of a test based on bacteria obtained in this way, comparing the data with legal limits. A scale-up process was developed with industrial technology: freeze-dried bacteria that emitted a stable luminous signal after rehydration were obtained. Moreover, the median effective concentration (EC50) was calculated with these bacteria.

Physiological effects of arsenic in the lichen Xanthoria parietina (L.) Th. Fr

The aim of this study was to test in a short term laboratory experiment the accumulation and physiological effects of As in the epiphytic lichen Xanthoria parietina. Arsenic content in treated samples increased progressively with increasing concentration in treatment solutions. Treatment of X. parietina thalli with 0.1, 1, 10 ppm As solutions caused significant decrease of viability, measured as intensity of respiratory activity, and damages to cell membranes, assessed by increase of electric conductivity of rinsing water and lipid peroxidation products. Soluble proteins content decreased and H₂O₂ content increased already at the lowest As concentration tested (0.01 ppm). Photosynthetic efficiency, measured in terms of F(V)/F(M) ratio, decreased significantly only at the highest As concentration (10 ppm). It was concluded that As exposure causes physiological stress both on the mycobiont and the photobiont and that cell membrane damage, expressed in terms of electric conductivity of rinsing water, is the parameter most affected by As treatment.

Wastewater canal Vojlovica, industrial complex Pancevo, Serbia: Preliminary ecotoxicological assessment of contaminated sediment

Effluents collected from the industrial complex of Pancevo, Serbia (oil refinery, petrochemical plant, and fertilizer factory) are discharged into a wastewater canal entering the Danube River. In this study, which was focused on sediment assessment, a complex triad approach consisting of chemical analysis, sediment toxicity tests and macrozoobenthos community analysis was applied. In toxicity tests on sediment elutriates, the following responses were registered - stimulatory effect in algal bioassay, no effect in acute test with Daphnia magna, and low to moderate toxicity in the conventional Vibrio fischeri test. Moderate to high toxicities were recorded in solid phase tests on Myriophyllum aquaticum and V. fischeri. High content of Hg, certain PAHs and noncharacterised sediment contaminants accumulated over years contribute not only to the registered toxicity, but also to the complete absence of macrozoobenthos. The obtained results proved that regularly measured conventional and priority pollutants are hardly ever the only toxic contaminants present in sediments. Toxicity tests, in particular the contact test, might guide towards a better selection of parameters to be regularly or occasionally monitored. In addition, complete sediment toxicity tests proved to be an appropriate method for assessing the bioavailability of the chemically detected contaminants. The analysis of the macrozoobenthos composition and structure as inevitable part of sediment risk assessment procedures integrates the effects of multiple stressors and gives a realistic insight into not only sediment contamination by toxic pollutants, but also the sediment status in general.

Interactive effects of cadmium and hypoxia on metabolic responses and bacterial loads of eastern oysters Crassostrea virginica Gmelin

Pollution by toxic metals including cadmium (Cd) and hypoxia are important stressors in estuaries and coastal waters which may interactively affect sessile benthic organisms, such as oysters. We studied metabolic responses to prolonged hypoxic acclimation (2 weeks at 5% O2) in control and Cd-exposed (30 d at 50 μg L(-1) Cd) oysters Crassostrea virginica, and analyzed the effects of these stressors on abundance of Vibrio spp. in oysters. Hypoxia-acclimated oysters retained normal standard metabolic rates (SMR) at 5% O2, in contrast to a decline of SMR observed during acute hypoxia. However, oysters spent more time actively ventilating in hypoxia than normoxia resulting in enhanced Cd uptake and 2.7-fold higher tissue Cd burdens in hypoxia. Cd exposure led to a significant decrease in tissue glycogen stores, increase in free glucose levels and elevated activity of glycolytic enzymes (hexokinase and aldolase) indicating a greater dependence on carbohydrate catabolism. A compensatory increase in activities of two key mitochondrial enzymes (citrate synthase and cytochrome c oxidase) was found during prolonged hypoxia in control oysters but suppressed in Cd-exposed ones. Cd exposure also resulted in a significant increase in abundance of Vibrio parahaemolyticus and Vibrio vulnificus levels during normoxia and hypoxia, respectively. Overall, Cd- and hypoxia-induced changes in metabolic profile, Cd accumulation and bacterial flora of oysters indicate that these stressors can synergistically impact energy homeostasis, performance and survival of oysters in polluted estuaries and have significant consequences for transfer of Cd and bacterial pathogens to the higher levels of the food chain.

Isolation of Photobacterium sp. LuB-1 and its application in rapid assays for chemical toxicants in water

AIMS

To isolate marine bacteria with strong bioluminescence in a wide range of NaCl concentration, especially at low salt conditions.

METHODS AND RESULTS

A luminous bacterium named LuB-1 was isolated from China. It was identified by biochemical analysis and phylogenetic analysis based on the 16S rRNA gene and designated as Photobacterium sp. The isolate is capable of emitting strong and stable luminescence in a wide range of NaCl concentration from 0.2 to 5% (w/v). For most toxic agents tested in this study, the response of LuB-1 was better than that of MicrotoxVibrio fischeri under both low salt (0.9% NaCl) and high salt (2.0% NaCl) conditions.

CONCLUSION

The strain LuB-1 had an obvious predominance of bioluminescence in a wide range of NaCl concentration and better response for heavy metal pollutants and some organic toxicants in both low and high salt toxicity test systems.

SIGNIFICANCE AND IMPACT OF THE STUDY

Because of its good sensitivity in a wide range of salt concentration, the strain LuB-1 should have its unique advantage in rapid assay for toxicants in water with different salt concentrations.

Sensitivity of bacterial vs. acute Daphnia magna toxicity tests to metals

The objectives of this study were to evaluate the sensitivity of two bacterial tests commonly used in metal toxicity screening — the Vibrio fischeri bioluminescence inhibition test and the Pseudomonas putida growth inhibition test — in comparison to the standard acute Daphnia magna test, and to estimate applicability of the selected methods to the toxicity testing of environmental samples. The D. magna acute test proved to be more sensitive to cadmium (Cd), zinc (Zn) and manganese (Mn) than the two bacterial assays, whereas P. putida seems to be the most sensitive species to lead (Pb). Manganese appears to be slightly toxic to D. magna and non-toxic to the two selected bacteria. This leads to the conclusion that even in regions with high background concentrations, manganese would not act as a confounding factor. Low sensitivity of V. fischeri to heavy metals questions its applicability as the first screening method in assessing various environmental samples. Therefore, it is not advisable to replace D. magna with bacterial species for metal screening tests. P. putida, V. fischeri and/or other bacterial tests should rather be applied in a complex battery of ecotoxicological tests, as their tolerance to heavy metals can unravel other potentially present toxic substances and mixtures, undetectable by metal-sensitive species.

Bioreactivity of municipal solid waste landfill leachates-Hormesis and DNA damage

The issue of domestic waste is recognised as one of the most serious environmental problems facing the nation. With the UK producing 35 million tonnes of municipal solid waste per annum, an understanding of the ranges of toxicity of landfill emissions is crucial to determine the degree of concern we should have about the potential effects these waste sites could have upon nearby populations and the surrounding environment. The aim of this study was to evaluate the bioreactivity of landfill leachates in terms of their capacity to damage ROS-sensitive bacteriophage plasmid DNA and induce toxicity in a commercial photobacterium toxicity assay, based on the light emission of Vibrio fischeri bacteria (ROTAS). The bacterial assay revealed widespread biostimulation and a hormesis response in the bacteria, with alpha-, beta- and gamma-response curves observed following exposure to the different landfill leachates. Different biological mechanisms lead to variations in bioreactivity, as seen in the plasmid DNA scission and ROTAS assays.

Monitoring of environmental pollutants by bioluminescent bacteria

This review deals with the applications of bioluminescent bacteria to the environmental analyses, published during the years 2000-2007. The ecotoxicological assessment, by bioassays, of the environmental risks and the luminescent approaches are reported. The review includes a brief introduction to the characteristics and applications of bioassays, a description of the characteristics and applications of natural bioluminescent bacteria (BLB), and a collection of the main applications to organic and inorganic pollutants. The light-emitting genetically modified bacteria applications, as well as the bioluminescent immobilized systems and biosensors are outlined. Considerations about commercially available BLB and BLB catalogues are also reported. Most of the environmental applications, here mentioned, of luminescent organisms are on wastewater, seawater, surface and ground water, tap water, soil and sediments, air. Comparison to other bioindicators and bioassay has been also made. Various tables have been inserted, to make easier to take a rapid glance at all possible references concerning the topic of specific interest.

Non-linear effects in the formation of DNA damage in medaka fish fibroblast cells caused by combined action of cadmium and ionizing radiation

Ionizing radiation-induced formation of genomic DNA damage can be modulated by nearby chemical species such as heavy metal ions, which can lead to non-linear dose response. To investigate this phenomenon, we studied cell survival and formation of 8-hydroxyguanine (8-OHG) base modifications and double strand breaks (DSB) caused by combined action of cadmium (Cd) and gamma radiation in cultured medaka fish (Oryzias latipes) fibroblast cells. Our data show that the introduction of Cd leads to a significant decrease in the fraction of surviving cells and to increased sensitivity of cells to ionizing radiation (IR). Cd also appears to cause non-linear increases in radiation-induced yields of 8-OHG and DSB as dose-yield plots of these lesions exhibit non-linear S-shaped curves with a sharp increase in the yields of lesions in the 10-20 microM range of Cd concentrations. The combined action of ionizing radiation and Cd leads to increased DNA damage formation compared to the effects of the individual stressors. These results are consistent with a hypothesis that the presence of Cd modulates the efficiency of DNA repair systems thus causing increases in radiation-induced DNA damage formation and decreases in cell survival.

Cr(VI) reduction into Cr(III) as a mechanism to explain the low sensitivity of Vibrio fischeri bioassay to detect chromium pollution

Vibrio fischeri bacteria, used as a biological target in either acute or chronic toxicity tests, display a low sensitivity to Cr(VI). This phenomenon could be due to the capacity of these bacteria to reduce Cr(VI) into Cr(III). This reducing capacity was found to depend on culture medium composition, pH value, incubation time and the presence of a carbon source. It also depends on the nature of the carbon source, glucose being more efficient than glycerol. This is probably related to differences in bacterial metabolism when given either glucose or glycerol. The thermostable Cr(VI)-reducing activity found in the supernatants of V. fischeri cultures grown on glucose suggests that, under these conditions, the bacteria release non-proteic reducing substances which have not been identified yet.

Bioluminescent bacteria assay of veterinary drugs in excreta of food-producing animals

The residues of pharmacological treatments on food-producing animals, present in the manure dispersed on agricultural land, can impact environmental and human health through toxic, genotoxic, and drug-resistance development effects. Biotoxicity assays can easily reveal the presence of noxious substances and those based on bioluminescent bacteria (BLB) are particularly simple and rapid. A BLB assay was developed as microplate format by using various strains of Vibrio sp. and was employed to evaluate their response to pure antibiotic solutions and to residues extracted from excreta of antibiotic treated pigs and turkeys. The residues were quantified by HPLC analysis. The BLB assay can be proposed as an easy-to-perform screening tool to assess the presence of residues due to undeclared current, or recently ended, pharmacological treatments, as well as to evaluate their permanence in manure.

Effects of chromium(VI) and vanadium(V) on the lifespan of fish

The effect of chromium(VI) on the lifespan of laboratory-reared guppies (Poecilia reticulata) has been studied both in the absence and in the presence of the antioxidant D-mannitol, and it has been compared with that produced by vanadium(V). The three substances used as additives exhibited either a weak (D-mannitol), a moderate (chromate) or an acute (vanadate) toxicity to fish. Vanadate, with LC50 (7 days) = 3.84 x 10(-5) mol/L, was about ten times more toxic than chromate, with LC50 (7 days) = 3.42 x 10(-4) mol/L as a single additive and 4.27 x 10(-4) mol/L in the presence of d-mannitol. An increasing effect on the maximum lifespan of males was observed when the additives studied were used at low concentrations, either alone or in a binary combination, following the sequence: vanadate (14%) < D-mannitol (41%) < chromate + D-mannitol (57%) < chromate (69%). Of these substances, only chromate increased also the maximum lifespan of females (72%). The maximum lifespan showed a strong, positive correlation with the concentration of chromate for males (P = 0.00008) and a weaker, positive correlation (P = 0.116) for females. These results suggest the existence of a chemical-hormesis phenomenon that might be subjected to sexual-genre variability. Both the toxicity and the chemical-hormetic effect provoked by chromate were substantially decreased when it was used in combination with d-mannitol, and the possible causes for this double inhibition are briefly discussed.