A novel continuous toxicity test system using a luminously modified freshwater bacterium

Impact of Anchoring Groups on the Photocatalytic Performance of Iridium(III) Complexes and Their Toxicological Analysis

Three different iridium(III) complexes, labelled as Ir1-Ir3, each bearing a unique anchoring moiety (diethyl [2,2'-bipyridine]-4,4'-dicarboxylate, tetraethyl [2,2'-bipyridine]-4,4'-diylbis(phosphonate), or [2,2'-biquinoline]-4,4'-dicarboxylic acid), were synthesized to serve as photosensitizers. Their electrochemical and photophysical characteristics were systematically investigated. ERP measurements were employed to elucidate the impact of the anchoring groups on the photocatalytic hydrogen generation performance of the complexes. The novel iridium(III) complexes were integrated with platinized TiO2 (Pt-TiO2) nanoparticles and tested for their ability to catalyze hydrogen production under visible light. A H2 turnover number (TON) of up to 3670 was obtained upon irradiation for 120 h. The complexes with tetraethyl [2,2'-bipyridine]-4,4'-diylbis(phosphonate) anchoring groups were found to outperform those bearing other moieties, which may be one of the important steps in the development of high-efficiency iridium(III) photosensitizers for hydrogen generation by water splitting. Additionally, toxicological analyses found no significant difference in the toxicity to luminescent bacteria of any of the present iridium(III) complexes compared with that of TiO2, which implies that the complexes investigated in this study do not pose a high risk to the aquatic environment compared to TiO2.

Development of an Improved Sulfur-Oxidizing Bacteria-Based Ecotoxicity Test for Simple and Rapid On-Site Application

Microbial toxicity tests are considered efficient screening tools for the assessment of water contamination. The objective of this study was to develop a sulfur-oxidizing bacteria (SOB)-based ecotoxicity test with high sensitivity and reproducibility for simple and rapid on-site application. To attain this goal, we developed a 25 mL vial-based toxicity kit and improved our earlier SOB toxicity test technique. The current study applied a suspended form of SOB and shortened the processing time to 30 min. Moreover, we optimized the test conditions of the SOB toxicity kit in terms of initial cell density, incubating temperature, and mixing intensity during incubation. We determined that 2 × 10⁵ cells/mL initial cell density, 32 °C incubating temperature, and 120 rpm mixing intensity are the optimal test conditions. Using these test conditions, we performed SOB toxicity tests for heavy metals and petrochemicals, and obtained better detection sensitivity and test reproducibility, compared to earlier SOB tests. Our SOB toxicity kit tests have numerous advantages, including a straightforward test protocol, no requirement of sophisticated laboratory equipment, and no distortion of test results from false readings of end-points and properties of test samples, making it suitable for simple and rapid on-site application.

Microbial fuel cell soft sensor for real-time toxicity detection and monitoring

Real-time toxicity detection and monitoring using a microbial fuel cell (MFC) is often based on observing current or voltage changes. Other methods of obtaining more information on the internal state of the MFC, such as electrochemical impedance spectroscopy (EIS), are invasive, disruptive, time consuming, and may affect long-term MFC performance. This study proposes a soft sensor approach as a non-invasive real-time method for evaluating the internal state of an MFC biosensor during toxicity monitoring. The proposed soft sensor approach is based on estimating the equivalent circuit model (ECM) parameters in real time. A flow-through MFC biosensor was operated at several combinations of carbon source (acetate) and toxicant (copper) concentrations. The ECM parameters, such as internal resistance, capacitance, and open-circuit voltage, were estimated in real time using a numerical parameter estimation procedure. The soft sensor approach proved to be an adequate replacement for EIS measurements in quantifying changes in the biosensor internal parameters. The approach also provided additional information, which could lead to earlier detection of the toxicity onset.

A simple and rapid algal assay kit to assess toxicity of heavy metal-contaminated water

This study presents a novel algal-based toxicity test suitable for simple and rapid assessment of heavy metal (Hg2+, Cr6+, Cd2+, Pb2+, or As3+)-contaminated water. A closed-system kit-type algal assay was developed using Chlorella vulgaris. Toxicity was assessed by oxygen evolution in the gaseous phase of the assay kits, which was measured via a needle-type oxygen sensor. Initial cell density, light intensity, and exposure time that enabled favorable test performance for the algal assay kits were 103 cells/mL, 250 μmol m-2s-1, and 18 h, respectively. Results from the heavy metal toxicity tests demonstrate that Hg2+, Cr6+, Cd2+, and Pb2+ are more toxic in inhibiting algal photosynthetic activity than As3+. The 18 h half-maximum effective concentrations (EC50) for Hg2+, Cr6+, Cd2+, Pb2+, and As3+ were determined to be 31.3 ± 0.5, 179.6 ± 7.5, 301.3 ± 6.1, 476.1 ± 10.5, and 2184.1 ± 31.1 μg/L, respectively. A strong correlation between oxygen concentrations in the headspace of the assay kits and chlorophyll a production indicates that oxygen evolution in the gaseous phase is able to represent algal photosynthetic activity and serve as the end-point in algal toxicity tests. High test sensitivity and reproducibility as well as an easy test protocol and rapid processing time make the algal assay kit a suitable tool for simple and rapid toxicity testing of heavy metal-contaminated water.

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.

Improved toxicity analysis of heavy metal-contaminated water via a novel fermentative bacteria-based test kit

The objective of this study was development of a simple and reliable microbial toxicity test based on fermentative bacteria to assess heavy metal (Hg²⁺, Cu²⁺, Cr⁶⁺, Ni²⁺, As⁵⁺, or Pb²⁺)-contaminated water. The dominant species of test organisms used in this study was a spore-forming fermentative bacterium, Clostridium guangxiense. Toxicity of water was assessed based on inhibition of fermentative gas production of the test organisms, which was analyzed via a syringe method. Overall, the fermentative bacteria-based test kits satisfactorily identified increased toxicity of water as water was contaminated with high amounts of heavy metals; however, levels of inhibition were dissimilar depending on the species of metals. Inhibitory effects of Hg²⁺, Cu²⁺, Cr⁶⁺, and Ni²⁺ were considerably greater than those of As⁵⁺ and Pb²⁺. The 24 h half-maximum effective concentrations (EC₅₀) for Hg²⁺, Cu²⁺, Cr⁶⁺, Ni²⁺, As⁵⁺, and Pb²⁺ were analyzed to be 0.10, 0.51, 1.09, 3.61, 101.33, and 243.45 mg/L, respectively, confirming that Hg²⁺, Cu²⁺, Cr⁶⁺, and Ni²⁺ are more toxic to fermentative gas production than As⁵⁺ and Pb²⁺. The fermentative bacteria-based toxicity test represents an improvement over other existing toxicity tests because of ease of end-point measurement, high reproducibility, and favorable on-site field applicability. These advantages make the fermentative bacteria-based test suitable for simple and reliable toxicity screening for heavy metal-contaminated water.

Ecotoxicity of phenol and cresols to aquatic organisms: A review

With the development of industrial production and continuous demand for chemicals, a large volume of wastewater containing phenols was discharged into the aquatic environment. Moreover, chemical leakage further increased the emission of phenols into aquatic systems. Phenol and its methylated derivative (cresols) were selected due to their extensive use in industry and ecotoxicity to freshwater and marine organisms. This review focused on the ecotoxicity of phenol and m-, o-, and p-cresol on aquatic systems. The mechanism of action of phenols was also discussed. The aim of this literature review was to summarise the knowledge of the behaviour, and toxicity on marine and freshwater organisms, of phenols as well as to try to select a series of sensitive biomarkers suitable for ecotoxicological assessment and environmental monitoring in aquatic environments.

Microplate freeze-dried cyanobacterial bioassay for fresh-waters environmental monitoring

Microorganisms have been very useful in environmental monitoring due to their constant sensing of the surrounding environment, their easy maintenance and low cost. Some freeze-dried toxicity kits based on naturally bioluminescent bacteria are commercially available and commonly used to assess the toxicity of environmental samples such as Microtox (Aliivibrio fischeri) or ToxScreen (Photobacterium leiognathi), however, due to the marine origin of these bacteria, they could not be the most appropriate for fresh-waters monitoring. Cyanobacteria are one of the most representative microorganisms of aquatic environments, and are well suited for detecting contaminants in aqueous samples. This study presents the development and application of the first freeze-dried cyanobacterial bioassay for fresh-water contaminants detection. The effects of different cell growth phases, cryoprotectant solutions, freezing protocols, rehydration solutions and incubation conditions methods were evaluated and the best combination of these parameters for freeze-drying was selected. The study includes detailed characterization of sensitivity towards reference pollutants, as well as, comparison with the standard assays. Moreover, long-term viability and sensitivity were evaluated after 3 years of storage. Freeze-dried cyanobacteria showed, in general, higher sensitivity than the standard assays and viability of the cells remained after 3 years of storage. Finally, the validation of the bioassay using a wastewater sample was also evaluated. Freeze-drying of cyanobacteria in 96-well plates presents a simple, fast and multi-assay method for environmental monitoring.

Comparison of chromium III and VI toxicities in water using sulfur-oxidizing bacterial bioassays

The toxicities of Cr (III) and Cr (VI) in water were evaluated using sulfur-oxidizing bacterial (SOB) bioassays both in batch and fed-batch conditions. Two days were enough for a quick buildup of SOB consortium in the master culture reactor (MCR). At concentrations up to 100 mg L(-1), Cr (III) was found to be nontoxic in both conditions, while Cr (VI) at very low concentrations (0.1-2 mg L(-1)) was very toxic to the SOB. Literature review suggested that the nontoxic nature of Cr (III) might be due to the absence of the iron uptake pathway in Acidithiobacillus caldus (the predominant bacteria in our reactors), which is required for Cr (III) uptake. The 2-h median effective concentration (EC50) values obtained for Cr (VI) in the batch and fed-batch tests were 2.7 mg L(-1) and 1.5 mg L(-1), respectively.

Photobiosensors containing luminescent bacteria

The scientific basis for producing luminescent biosensors containing free and immobilized luminescent bacteria is discussed. Modern technologies for engineering target objects, procedures used to immobilize bacteria in different carriers, as well as procedures for integral and specific biodetection of toxins are presented. Data regarding generation and application of biomonitoring for ecotoxicants derived from natural and genetically engineered photobacterial strains are analyzed. Special attention is given to immobilization of photobacteria in polyvinyl alcohol-containing cryogel. The main physicochemical, biochemical, and technological parameters for stabilizing luminescence in immobilized bacteria are described. Results of the application of immobilized photobacterial preparations both during discrete and continuous biomonitoring for different classes of ecotoxicants are presented.

Deacylated lipopolysaccharides inhibit biofilm formation by Gram-negative bacteria

The extracellular polysaccharides of Vibrio vulnificus play different roles during biofilm development. Among them, the effect of lipopolysaccharide (LPS), which is crucial for bacterial adherence to surfaces during the initial stage of biofilm formation, on the formation process was examined using various types of LPS extracts. Exogenously added LPS strongly inhibited biofilm formation in a dose-dependent manner. In addition, the exogenous addition of a deacylated form of LPS (dLPS) also inhibited biofilm formation. However, an LPS fraction extracted from a mutant not able to produce O-antigen polysaccharides (O-Ag) did not have an inhibitory effect. Furthermore, biofilm formation by several Gram-negative bacteria was inhibited by dLPS addition. In contrast, biofilm formation by Gram-positive bacteria was not influenced by dLPS but was affected by lipoteichoic acid. Therefore, this study demonstrates that O-Ag in LPS is important for inhibiting biofilm formation and may serve an efficient anti-biofilm agent specific for Gram-negative bacteria.

Adaptive use of a personal glucose meter (PGM) for acute biotoxicity assessment based on the glucose consumption of microbes

In this study, a new method for acute biotoxicity assessment was proposed by measuring the glucose consumption of microbes with a personal glucose meter (PGM).

Main Technological Advancements in Bacterial Bioluminescent Biosensors Over the Last Two Decades

Environmental quality assessment is an extensive field of research due to the permanent increase of the stringency imposed by the legislative framework. To complete the wide panel of measurement methods, essentially based on physicochemical tools, some scientists focused on the development of alternative biological methods such as those based on the use of bioluminescent bacteria biosensors. The first report dedicated to the development of such biosensors dates back to 1967 and describes an analytical system designed to address the problem of air toxicity assessment. Nevertheless the available technologies in the photosensitive sensors field were not mature enough and, as a result, limited biosensor development possibilities. For about 20 years, the wide democratisation of photosensors coupled with advances in the genetic engineering field have allowed the expansion of the scope of possibilities of bioluminescent bacterial biosensors, allowing a significant emergence of these biotechnologies. This chapter retraces the history of the main technological evolutions that bacterial bioluminescent biosensors have known over the last two decades. Graphical Abstract.

Anthropogenic Trace Compounds (ATCs) in aquatic habitats - research needs on sources, fate, detection and toxicity to ensure timely elimination strategies and risk management

Anthropogenic Trace Compounds (ATCs) that continuously grow in numbers and concentrations are an emerging issue for water quality in both natural and technical environments. The complex web of exposure pathways as well as the variety in the chemical structure and potency of ATCs represents immense challenges for future research and policy initiatives. This review summarizes current trends and identifies knowledge gaps in innovative, effective monitoring and management strategies while addressing the research questions concerning ATC occurrence, fate, detection and toxicity. We highlight the progressing sensitivity of chemical analytics and the challenges in harmonization of sampling protocols and methods, as well as the need for ATC indicator substances to enable cross-national valid monitoring routine. Secondly, the status quo in ecotoxicology is described to advocate for a better implementation of long-term tests, to address toxicity on community and environmental as well as on human-health levels, and to adapt various test levels and endpoints. Moreover, we discuss potential sources of ATCs and the current removal efficiency of wastewater treatment plants (WWTPs) to indicate the most effective places and elimination strategies. Knowledge gaps in transport and/or detainment of ATCs through their passage in surface waters and groundwaters are further emphasized in relation to their physico-chemical properties, abiotic conditions and biological interactions in order to highlight fundamental research needs. Finally, we demonstrate the importance and remaining challenges of an appropriate ATC risk assessment since this will greatly assist in identifying the most urgent calls for action, in selecting the most promising measures, and in evaluating the success of implemented management strategies.

An optical biosensor from green fluorescent Escherichia coli for the evaluation of single and combined heavy metal toxicities

A fluorescence-based fiber optic toxicity biosensor based on genetically modified Escherichia coli (E. coli) with green fluorescent protein (GFP) was developed for the evaluation of the toxicity of several hazardous heavy metal ions. The toxic metals include Cu(II), Cd(II), Pb(II), Zn(II), Cr(VI), Co(II), Ni(II), Ag(I) and Fe(III). The optimum fluorescence excitation and emission wavelengths of the optical biosensor were 400 ± 2 nm and 485 ± 2 nm, respectively. Based on the toxicity observed under optimal conditions, the detection limits of Cu(II), Cd(II), Pb(II), Zn(II), Cr(VI), Co(II), Ni(II), Ag(I) and Fe(III) that can be detected using the toxicity biosensor were at 0.04, 0.32, 0.46, 2.80, 100, 250, 400, 720 and 2600 μg/L, respectively. The repeatability and reproducibility of the proposed biosensor were 3.5%–4.8% RSD (relative standard deviation) and 3.6%–5.1% RSD (n = 8), respectively. The biosensor response was stable for at least five weeks, and demonstrated higher sensitivity towards metal toxicity evaluation when compared to a conventional Microtox assay.

Review of micro/nanotechnologies for microbial biosensors

A microbial biosensor is an analytical device with a biologically integrated transducer that generates a measurable signal indicating the analyte concentration. This method is ideally suited for the analysis of extracellular chemicals and the environment, and for metabolic sensory regulation. Although microbial biosensors show promise for application in various detection fields, some limitations still remain such as poor selectivity, low sensitivity, and impractical portability. To overcome such limitations, microbial biosensors have been integrated with many recently developed micro/nanotechnologies and applied to a wide range of detection purposes. This review article discusses micro/nanotechnologies that have been integrated with microbial biosensors and summarizes recent advances and the applications achieved through such novel integration. Future perspectives on the combination of micro/nanotechnologies and microbial biosensors will be discussed, and the necessary developments and improvements will be strategically deliberated.

Promising Biological Indicator of Heavy Metal Pollution: Bioluminescent Bacterial Strains Isolated and Characterized from Marine Niches of Goa, India

In present study, several marine water samples collected from the North Goa Beaches, India for isolation of luminescent bacterial species. Isolates obtained labelled as DP1-5 and AB1-6. Molecular characterization including identification of a microbial culture using 16S rRNA gene based molecular technique and phylogenetic analysis confirmed that DP3 & AB1 isolates were Vibrio harveyi. All of the isolates demonstrated multiple metal resistances in terms of growth, with altered luminescence with variable metal concentration. Present investigations were an attempt towards exploring and reporting an updated diversity of bioluminescent bacterial species from various sites around the Goa, India which would be explored in future for constructing luminescence based biosensor for efficiently monitoring the level of hazardous metals in the environment.

Microencapsulated Aliivibrio fischeri in alginate microspheres for monitoring heavy metal toxicity in environmental waters

In this article a luminescence fiber optic biosensor for the microdetection of heavy metal toxicity in waters based on the marine bacterium Aliivibrio fischeri (A. fischeri) encapsulated in alginate microspheres is described. Cu(II), Cd(II), Pb(II), Zn(II), Cr(VI), Co(II), Ni(II), Ag(I) and Fe(II) were selected as sample toxic heavy metal ions for evaluation of the performance of this toxicity microbiosensor. The loss of bioluminescence response from immobilized A. fischeri bacterial cells corresponds to changes in the toxicity levels. The inhibition of the luminescent biosensor response collected at excitation and emission wavelengths of 287 ± 2 nm and 487 ± 2 nm, respectively, was found to be reproducible and repeatable within the relative standard deviation (RSD) range of 2.4-5.7% (n = 8). The toxicity biosensor based on alginate micropsheres exhibited a lower limit of detection (LOD) for Cu(II) (6.40 μg/L), Cd(II) (1.56 μg/L), Pb(II) (47 μg/L), Ag(I) (18 μg/L) than Zn(II) (320 μg/L), Cr(VI) (1,000 μg/L), Co(II) (1700 μg/L), Ni(II) (2800 μg/L), and Fe(III) (3100 μg/L). Such LOD values are lower when compared with other previous reported whole cell toxicity biosensors using agar gel, agarose gel and cellulose membrane biomatrices used for the immobilization of bacterial cells. The A. fischeri bacteria microencapsulated in alginate biopolymer could maintain their metabolic activity for a prolonged period of up to six weeks without any noticeable changes in the bioluminescence response. The bioluminescent biosensor could also be used for the determination of antagonistic toxicity levels for toxicant mixtures. A comparison of the results obtained by atomic absorption spectroscopy (AAS) and using the proposed luminescent A. fischeri-based biosensor suggests that the optical toxicity biosensor can be used for quantitative microdetermination of heavy metal toxicity in environmental water samples.

Fluorescent and bioluminescent cell-based sensors: strategies for their preservation

Luminescent whole-cell biosensing systems have been developed for a variety of analytes of environmental, clinical, and biological interest. These analytical tools allow for sensitive, rapid, simple, and inexpensive quantitative detection of target analytes. Furthermore, they can be designed to be nonspecific, semispecific, or highly specific/selective. A notable feature of such sensing systems employing living cells is that they provide information on the analyte bioavailability and activity. These characteristics, along with their suitability to miniaturization, make cell-based sensors ideal for field applications. However, a major limitation to on-site use is their "shelf-life." To address this problem, various methods for preservation of sensing cells have been reported, including freeze-drying, immobilization in different types of matrices, and formation of spores. Among these, the use of spores emerged as a promising strategy for long-term storage of whole-cell sensing systems at room temperature as well as in extreme environmental conditions.

Assessment of chromium-contaminated groundwater using a thiosulfate-oxidizing bacteria (TOB) biosensor

The effect of Cr(6+)-contaminated groundwater was assessed using thiosulfate-oxidizing bacteria (TOB). Electrical conductivity (EC), pH, and sulfate production were determined based on thiosulfate oxidation. Final pH values in the different test treatments of Cr(6+)-contaminated groundwater (50-1000 μg Cr(6+)L(-1)) ranged from 2.02 ± 0.09 to 7.76 ± 0.07 and EC ranged from 5.95 ± 0.03 to 3.63 ± 0.03 mS cm(-1). Inhibition of TOB due to Cr(6+) was between 16.7% and 100%, with higher levels of inhibition occurring at higher Cr(6+) concentrations. The median effective concentration (EC50) was 78.96 μg Cr(6+)L(-1). These data demonstrate that TOB can detect less than 100 μg L(-1) of Cr(6+) in the groundwater and can be used as an effective bioassay for toxicity assessment.

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.

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.

Altered toxicity of organic pollutants in water originated from simultaneous exposure to UV photolysis and CdSe/ZnS quantum dots

The paper reports unforeseen results of increased toxicity of water, subsequent to interactions between CdSe/ZnS quantum dots (QDs), phenol and toluene under UV irradiation. The consistent pattern of changes in measured toxicity (TU) was observed and correlated with degradation of phenol and/or toluene. Spearman rank coefficients (SRCs) for data pairs sum-parameters vs. TU were calculated. The highest correlation between toxicity and degradation by-products was observed for hydroquinone (0.86) and catechol (0.89). The presence of QDs in tested concentration range in the absence of UV has shown low toxicity and no interactions with phenol and/or toluene. The leak of constituent core and shell metal ions was observed. The minor differences in physical characteristics of tested QDs of the same chemical composition led to rather different degradation patterns of phenol and toluene, and the amount of leak of the metal ions as well.

Detection of Cr6+ by the sulfur oxidizing bacteria biosensor: effect of different physical factors

A biosensor based on sulfur-oxidizing bacteria (SOB) for detection of toxic chemicals in water was developed. SOB are acidophilic microorganisms that get their energy through the oxidation of reduced sulfur compounds in the presence of oxygen to produce sulfuric acid. The reaction results in an increase in electrical conductivity (EC) and a decrease in pH. The bioassay is based on the inhibition of SOB in the presence of toxic chemicals by measuring changes in EC and pH. The effect of different physical factors such as HRT, inorganic sulfur (S°) particle size, and temperature on detection of Cr(6+) was studied. The detection of Cr(6+) (50 ppb) was improved by decreasing the hydraulic retention time (HRT) from 30 to 10 min and increasing S° particle size from 1 to 4.75 mm. Detection time was shorter at 30 °C compared to 45 °C and the SOB were active over a wide range of temperatures with a maximum temperature for growth at 45 °C. This novel biosensor is simple, highly sensitive to low Cr(6+) concentrations (50 ppb), and also minimizes detection time. The present findings can be applied to the proper continuous screening of water ecosystem toxicity.

Detecting oxidized contaminants in water using sulfur-oxidizing bacteria

For the rapid and reliable detection of oxidized contaminants (i.e., nitrite, nitrate, perchlorate, dichromate) in water, a novel toxicity detection methodology based on sulfur-oxidizing bacteria (SOB) has been developed. The methodology exploits the ability of SOB to oxidize elemental sulfur to sulfuric acid in the presence of oxygen. The reaction results in an increase in electrical conductivity (EC) and a decrease in pH. When oxidized contaminants were added to the system, the effluent EC decreased and the pH increased due to the inhibition of the SOB. We found that the system can detect these contaminants in the 5-50 ppb range (in the case of NO(3)(-), 10 ppm was detected), which is lower than many whole-cell biosensors to date. At low pH, the oxidized contaminants are mostly in their acid or nonpolar, protonated form which act as uncouplers and make the SOB biosensor more sensitive than other whole-cell biosensors which operate at higher pH values where the contaminants exist as dissociated anions. The SOB biosensor can detect toxicity on the order of minutes to hours which can serve as an early warning so as to not pollute the environment and affect public health.

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.

Applications of microbial cell sensors

Since the first microbial cell sensor was studied by Karube et al. in 1977, many types of microbial cell sensors have been developed as analytical tools. The microbial cell sensor utilizes microbes as a sensing element and a transducer. The characteristics of microbial cell sensors as sensing devices are a complete contrast to those of enzyme sensors or immunosensors, which are highly specific for the substrates of interest, although the specificity of the microbial cell sensor has been improved by genetic modification of the microbe used as the sensing element. Microbial cell sensors have the advantages of tolerance to measuring conditions, a long lifetime, and good cost performance, and have the disadvantage of a long response time. In this review, applications of microbial cell sensors are summarized.

Oxygen flux as an indicator of physiological stress in fathead minnow (Pimephales promelas) embryos: a real-time biomonitoring system of water quality

The detection of harmful chemicals and biological agents in real time is a critical need for protecting freshwater ecosystems. We studied the real-time effects of five environmental contaminants with differing modes of action (atrazine, cadmium chloride, pentachlorophenol, malathion, and potassium cyanide) on respiratory oxygen consumption in 2-day postfertilization fathead minnow (Pimephales promelas) eggs. Our objective was to assess the sensitivity of fathead minnow eggs using the self-referencing micro-optrode technique to detect instantaneous changes in oxygen consumption after brief exposures to low concentrations of contaminants. Oxygen consumption data indicated that the technique is indeed sensitive enough to reliably detect physiological alterations induced by four of the five contaminants. After 2 h of exposure, we identified significant increases in oxygen consumption upon exposure to pentachlorophenol (100 and 1000 microg/L), cadmium chloride (0.0002 and 0.002 microg/L), and atrazine (150 microg/L). In contrast, we observed a significant decrease in oxygen flux after exposuresto potassium cyanide (44 and 66 microg/L) and atrazine (1500 microg/L). No effects were detected after exposures to malathion (200 and 340 microg/L). Our work is the first step in development of a new technique for physiologically coupled biomonitoring as a sensitive and reliable tool for the detection of environmental toxicants.

Development of microbial sensors and their application

Many types of microbial sensors have been developed as analytical tools since the first microbial sensor was studied by Karube et al. in 1977. The microbial sensor consists of a transducer and microbe as a sensing element. The characteristics of the microbial sensors are a complete contrast to those of enzyme sensors or immunosensors, which are highly specific for the substrates of interest, although the specificity of the microbial sensor has been improved by genetic modification of the microbe used as the sensing element. Microbial sensors have the advantages of tolerance to measuring conditions, a long lifetime, and cost performance, and also have the disadvantage of a long response time. In this review, the long history of microbial sensor development is summarized.

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.

Chemical-specific continuous biomonitoring using a recombinant bioluminescent bacterium DNT5 (nagR-nagAa::luxCDABE)

The recombinant bioluminescent bacterium, DNT5, containing a nagR-nagAa::luxCDABE fusion, was tested in a multi-channel continuous monitoring system to evaluate its ability to detect benzoic acid derivatives. Seven chemicals, benzoic acid, salicylic acid, 2,5-dihydroxy benzoic acid, 3,5-dihydroxy benzoic acid, benzene, naphthalene and phenol, were used to characterize the responses of DNT5. This strain responded uniquely to each chemical, and these responses were then evaluated based upon the structures of each chemical. The greatest bioluminescent responses were to salicylic acid and benzoic acid, followed by 2,5-dihydroxy benzoic acid and 3,5-dihydroxy benzoic acid, but DNT5 was unresponsive when exposed to benzene, phenol and naphthalene, suggesting it has a strong preference for benzoic acid derivatives with few or no ring-substituted groups.

A set up of a modern analytical laboratory for wastewaters from pulp and paper industry

The introduction of analytical techniques allowing rapid, selective, sensitive, and reliable determination of aqueous pollutants is of crucial importance for the protection of the environment. This critical review summarizes the advanced analytical techniques suggested over the last ten years together with already established methods, and evaluates whether they are fit for wastewater quality assessment considering the area of application, interferences, limit of detection, calibration function, and precision. The key parameters of wastewater quality assessment are: total organic carbon (TOC), chemical oxygen demand (COD), biochemical oxygen demand (BOD), organochlorines (AOX), nitrogen, phosphorus, sulfur, and toxicity. Chromatography and capillary electrophoresis, photocatalytic oxidation with semiconductor nanofilms and atomic emission spectrometry, optical fibre sensors and chemiluminescence, amperometric mediated biosensors and microbial fuel cells, respirometry and bioluminescence measurements are just part of the proposed wastewater analyst's toolkit. The diversity of fundamental phenomena and the captivating elegance of interdisciplinary applications involved in the development of wastewater analytical techniques should attract the interest of a wide scientific audience including analytical chemists, chemical physicists, microbiologists and environmentalists. To conclude, we suggest a laboratory set up for the analysis of wastewaters from the pulp and paper industry.

Rapid and onsite BOD sensing system using luminous bacterial cells-immobilized chip

A BOD monitoring system based on a bio-chip which immobilized luminous bacterium in micrometer-order holes were arrayed and fabricated by micro-machine techniques, was developed. The acrylic chip (3 cmx3 cm) comprises nine micro-holes (diameter: 700 microm or 1 mm, depth: 100 microm) arranged in a three by three array. Cells of the marine luminous bacterium, Photobacterium phosphoreum IFO 13896, which was grown at 15 degrees C for 15 h, were immobilized with 3% or 15% sodium alginate gel. BOD standard solutions or actual sample solution (approximately 10 microl) was fallen onto the cell-arrayed chip, and then the chip was incubated at 25 degrees C for 25 min. After incubation, bioluminescence from the each hole was gray-scaled and measured by a chemi-imager or newly developed onsite-type-monitoring system using a digital camera and a mobile-type personal computer. BOD values less than 16 ppm could detect by the chip, in particular, linear relationship at the concentrations between 0 and 16 ppm could be observed when luminous cells were immobilized with 3% sodium alginate gel. Steady bioluminescence was observed on the chip in the presence of BOD standard solution (GGA solution) which contained mineral elements. Furthermore, simultaneous detection of BOD values in various samples could be employed in the single chip. These results showed that the monitoring system with bio-chip could achieve high-through-put and onsite BOD detection. Our newly developed onsite-type BOD detection system which was used a digital camera and a (mobile) laptop computer was applied to measure and detect organic pollution due to biodegradable substances in wastewater treatment system. The same performance as the chemi-imager system was obtained for data of bioluminescence. The obtained BOD values showed a similar correlation with that of the conventional method for BOD determination (BOD5). These results suggested for successful achievement of high-though-put and onsite detection of BOD in practical.

Recent advances in biosensor techniques for environmental monitoring

Biosensors for environmental applications continue to show advances and improvements in areas such as sensitivity, selectivity and simplicity. In addition to detecting and measuring specific compounds or compound classes such as pesticides, hazardous industrial chemicals, toxic metals, and pathogenic bacteria, biosensors and bioanalytical assays have been designed to measure biological effects such as cytotoxicity, genotoxicity, biological oxygen demand, pathogenic bacteria, and endocrine disruption effects. This article is intended to discuss recent advances in the area of biosensors for environmental applications.

Making bio-sense of toxicity: new developments in whole-cell biosensors

Bacterial whole-cell biosensors are very useful for toxicity measurements of various samples. Semi-specific biosensors, containing fusions of stress-regulated promoters and reporter genes, have several advantages over the traditional, general biosensors that are based on constitutively expressed reporter genes. Furthermore, semi-specific biosensors are constantly being refined to lower their sensitivity and, in combination, are able to detect a wide range of toxic agents. However, the requirement for a positive response of these biosensors to toxicants can result in false-negative responses. The application of in situ inoculation and single-cell detection, combined with the introduction of new reporter genes and refined detection equipment, could lead to the extensive use of semi-specific, stress-responsive biosensors for toxicity estimations in the future.