Development of bespoke bioluminescent reporters with the potential for in situ deployment within a phenolic-remediating wastewater treatment system

Pseudomonas putida biofilm dynamics following a single pulse of silver nanoparticles

Pseudomonas putida mono-species biofilms were exposed to silver nanoparticles (Ag NPs) in artificial wastewater (AW) under hydrodynamic conditions. Specifically, 48 h old biofilms received a single pulse of Ag NPs at 0, 0.01, 0.1, 1, 10 and 100 mg L(-1) for 24 h in confocal laser scanning microscopy (CLSM) compatible flow-cells. The biofilm dynamics (in terms of morphology, viability and activity) were characterised at 48, 72 and 96 h. Consistent patterns were found across flow-cells and experiments at 48 h. Dose dependent impacts of NPs were then shown at 72 h on biofilm morphology (e.g. biomass, surface area and roughness) from 0.01 mg L(-1). The microbial viability was not altered below 10 mg L(-1) Ag NPs. The activity (based on the d-glucose utilisation) was impacted by concentrations of Ag NPs equal and superior to 10 mg L(-1). Partial recovery of morphology, viability and activity were finally observed at 96 h. Comparatively, exposure to Ag salt resulted in ca. one order of magnitude higher toxicity when compared to Ag NPs. Consequently, the use of a continuous culture system and incorporation of a recovery stage extends the value of biofilm assays beyond the standard acute toxicity assessment.

Toxicity Testing of Pristine and Aged Silver Nanoparticles in Real Wastewaters Using Bioluminescent Pseudomonas putida

Impact of aging on nanoparticle toxicity in real matrices is scarcely investigated due to a lack of suitable methodologies. Herein, the toxicity of pristine and aged silver nanoparticles (Ag NPs) to a bioluminescent Pseudomonas putida bioreporter was measured in spiked crude and final wastewater samples (CWs and FWs, respectively) collected from four wastewater treatment plants (WWTPs). Results showed lower toxicity of pristine Ag NPs in CWs than in FWs. The effect of the matrix on the eventual Ag NP toxicity was related to multiple physico-chemical parameters (biological oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS) pH, ammonia, sulfide and chloride) based on a multivariate analysis. However, no collection site effect was concluded. Aged Ag NPs (up to eight weeks) were found less toxic than pristine Ag NPs in CWs; evident increased aggregation and decreased dissolution were associated with aging. However, Ag NPs exhibited consistent toxicity in FWs despite aging; comparable results were obtained in artificial wastewater (AW) simulating effluent. The study demonstrates the potency of performing nanoparticle acute toxicity testing in real and complex matrices such as wastewaters using relevant bacterial bioreporters.

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

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

Detection of organic compounds with whole-cell bioluminescent bioassays

Natural and manmade organic chemicals are widely deposited across a diverse range of ecosystems including air, surface water, groundwater, wastewater, soil, sediment, and marine environments. Some organic compounds, despite their industrial values, are toxic to living organisms and pose significant health risks to humans and wildlife. Detection and monitoring of these organic pollutants in environmental matrices therefore is of great interest and need for remediation and health risk assessment. Although these detections have traditionally been performed using analytical chemical approaches that offer highly sensitive and specific identification of target compounds, these methods require specialized equipment and trained operators, and fail to describe potential bioavailable effects on living organisms. Alternatively, the integration of bioluminescent systems into whole-cell bioreporters presents a new capacity for organic compound detection. These bioreporters are constructed by incorporating reporter genes into catabolic or signaling pathways that are present within living cells and emit a bioluminescent signal that can be detected upon exposure to target chemicals. Although relatively less specific compared to analytical methods, bioluminescent bioassays are more cost-effective, more rapid, can be scaled to higher throughput, and can be designed to report not only the presence but also the bioavailability of target substances. This chapter reviews available bacterial and eukaryotic whole-cell bioreporters for sensing organic pollutants and their applications in a variety of sample matrices.

Removal efficiency and toxicity reduction of 4-chlorophenol with physical, chemical and biochemical methods

Chlorophenols are well-known priority pollutants and many different treatments have been assessed to facilitate their removal from industrial wastewater. However, an absolute and optimum solution still has to be practically implemented in an industrial setting. In this work, a series ofphysical, chemical and biochemical treatments have been systematically tested for the removal of 4-chlorophenol, and their results have been compared in order to determine the most effective treatment based on removal efficiency and residual by-product formation. Chemical treatments based on advanced oxidation processes (AOP) produced the best results on rate and extent of pollutant removal. The non-chemical technologies showed advantages in terms of complete (in the case of adsorption) or easy (enzymatic treatments) removal of toxic treatment by-products. The AOP methods led to the production of different photoproducts depending on the chosen treatment. Toxic products remained in most cases following treatment, though the toxicity level is significantly reduced with combination treatments. Among the treatments, a photochemical method combining UV, produced with a KrCl excilamp, and hydrogen peroxide achieved total removal of chlorophenol and all by-products and is considered the best treatment for chlorophenol removal.

Silver nanotoxicity using a light-emitting biosensor Pseudomonas putida isolated from a wastewater treatment plant

The effect of silver ions, nano- and micro-particles on a luminescent biosensor bacterium Pseudomonas putida originally isolated from activated sludge was assessed. The bacterium carrying a stable chromosomal copy of the lux operon (luxCDABE) was able to detect toxicity of ionic and particulate silver over short term incubations ranging from 30 to 240 min. The IC(50) values obtained at different time intervals showed that highest toxicity (lowest IC(50)) was obtained after 90 min incubation for all toxicants and this is considered the optimum incubation for testing. The data show that ionic silver is the most toxic followed by nanosilver particles with microsilver particles being least toxic. Release of nanomaterials is likely to have an effect on the activated sludge process as indicated by the study using a common sludge bacterium involved in biodegradation of organic wastes.

Influence of phenolics on the sensitivity of free and immobilized bioluminescent Acinetobacter bacterium

In this work, the constructed bioluminescent Acinetobacter strain DF4/PUTK2 was employed to assess the toxicity of phenolic compounds and the 5 min EC50 values were calculated. The results of the DF4/PUTK2 assay were further evaluated by comparing with the results of the Vibrio fischeri luminescence inhibition assay. To develop a bioassay system appropriate to be used in continuous toxicity testing, strain DF4/PUTK2 was subjected for immobilization in microtiter plates into the matrices Ca-alginate, polyacrylamide, agar and agarose. After a choice of materials was tried, Ca-alginate was selected as the most suitable candidate material. Because, it could be stored at least 8 weeks at 4 degrees C, during which the ability of the bioreporter DF4/PUTK2 to detect the toxicity of phenolics was maintained. However, the stability of the bioluminescence for DF4/PUTK2 cells immobilized into agarose and agar was significantly less than that of cells stored in alginate suspensions. This study recommended that luxCDABE-marked Acinetobacter strain DF4/PUTK2 could be employed to assay the ecotoxicity of environmental samples contaminated with phenols. The host strain of the bioreporter DF4/PUTK2 is Acinetobacter strain DF4. It is known that members of the genus Acinetobacter are widespread in nature and also involved in biodegradation, leaching and removal of several organic and inorganic man-made hazardous wastes.

Inhibition of proliferation of Pseudomonas aeruginosa by KGF in an experimental burn model using human cultured keratinocytes

Experimental models showed the ability of Pseudomonas aeruginosa to interact with epidermal keratinocytes [Green H, Kehinde O, Thomas J. Growth of cultured human epidermal cells into multiple epithelia suitable for grafting. Proc Natl Acad Sci USA 1979;76(11):5665-8], stimulating these cells to produce specific peptides that start an immunological chain reaction in the epidermis [O'Connor NE, Mulliken JB, Banks-Schlegel S, Kehinde O, Green H. Grafting of burns with cultured epithelium prepared from autologous epidermal cells. Lancet 1981;(1):75-8]. The immune reaction causes the release of cytokines and growth factors. The objective of this study was to test whether the presence of keratinocyte growth factor (KGF) alters P. aeruginosa proliferation in an experimental burn model.

METHODS

Human keratinocytes derived from neonatal foreskins were isolated and cultured following standard methods [Gallico III, GG, O'Connor NE, Compton CC, Kehinde O, Green H. Permanent coverage of large burn wounds with autologous cultured human epithelium. N Engl J Med 1984;311(7):448-51]. Some of these cells were genetically modified to produce KGF, and the other cells were supplemented with different KGF concentrations in the culture media. Both groups of keratinocytes were seeded in collagen matrices and cultured to form stratified epithelia. A hot plate was used to produce burn defects. Each matrix was inoculated with luminescent P. aeruginosa strain. Experiments were made using keratinocytes without KGF, keratinocytes supplemented with different concentrations of KGF, and keratinocytes genetically modified to produce KGF. Statistical analyses were made using Wilcoxon paired test.

RESULTS

When KGF was added to P. aeruginosa in the presence of keratinocytes, bacterial growth was inhibited, and the same was observed when genetically modified keratinocytes were used.

CONCLUSION

Many studies have been done on KGF, where its known properties were defined as a mitogen for keratinocytes [Munster AM. Cultured skin for massive burns: a prospective, controlled trial. Ann Surg 1996;224(3):372-7]. This method allows for a qualitative and quantitative evaluation in real time of the bacterial growth in wound sites after bacterial inoculation. KGF was involved in the reduction of bacterial viability. However, as KGF alone did not produce any effect on P. aeruginosa, it seems to modulate the skin innate immune response.

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.

Biosensor-based diagnostics of contaminated groundwater: assessment and remediation strategy

Shallow groundwater beneath a former airfield site in southern England has been heavily contaminated with a wide range of chlorinated solvents. The feasibility of using bacterial biosensors to complement chemical analysis and enable cost-effective, and focussed sampling has been assessed as part of a site evaluation programme. Five different biosensors, three metabolic (Vibrio fischeri, Pseudomonas fluorescens 10568 and Escherichia coli HB101) and two catabolic (Pseudomonas putida TVA8 and E. coli DH5alpha), were employed to identify areas where the availability and toxicity of pollutants is of most immediate environmental concern. The biosensors used showed different sensitivities to each other and to the groundwater samples tested. There was generally a good agreement with chemical analyses. The potential efficacy of remediation strategies was explored by coupling sample manipulation to biosensor tests. Manipulation involved sparging and charcoal treatment procedures to simulate remediative engineering solutions. Sparging was sufficient at most locations.

Calibration and deployment of custom-designed bioreporters for protecting biological remediation consortia from toxic shock

We have previously described the development of a panel of site-specific lux-based bioreporters from an industrial wastewater treatment system remediating coking effluents. The Pseudomonad strains carry a stable chromosomal copy of the luxCDABE operon from Photorhabdus luminescens and display proportional responses in bioluminescence decay with increasing phenol concentration up to 800 mg l-1. In this work we describe their deployment to provide a strategic sensing network for protecting bacterial communities involved in the biological breakdown of coking effluents. This evaluation demonstrated the utility of strategic placement of reporters around heavy industry treatment systems and the reliability of the reporter strains under normal operational conditions. Mono-phenol or total phenolic variation within the treatment system accounted for>65-80% of the luminescence response. The reporters exhibited stable luminescence output during normal operations with maximum standard deviations of luminescence over time of c. 5-15% depending on the treatment compartment. Furthermore, deployment of the bioreporters over a 5-month period allowed the determination of an operational range (OR) for each reporter for effluent samples from each compartment. The OR allowed a convenient measure of toxicity effects between treatment compartments and accurately reflected a specific pollution event occurring within compartments of the treatment system. This work demonstrates the utility of genetic modification to provide ecologically relevant bioreporters, extends the sensing capabilities currently obtained through marine derived biosensors and significantly enhances the potential for in situ deployment of reporting agents.

Toxicity of metals and organic chemicals evaluated with bioluminescence assays

The development of a bioluminescent sensor organism (Shk1) that was created for assessing wastewater toxicity was reported several years ago. In order to establish a test battery to better characterize wastewater toxicity, additional luminescent sensor organisms were later created. The present study focused on one promising candidate (PM6), a Pseudomonas spp. strain, because of its high level of luminescence compared to that of other newly created organisms. Using a batch toxicity testing protocol, the toxicity of 7 metals and 25 organic compounds was evaluated with the PM6 and Shk1 assays. Results indicated that the toxicity data of the PM6 and the Shk1 assays were correlated, and no assay appeared to be particularly more sensitive to a group of toxicants than the other assay. The results of the PM6 and Shk1 assays were further evaluated by comparing with the results of the Vibrio fischeri luminescence inhibition assay and activated sludge inhibition assays. Data suggested that PM6 and Shk1 more closely represented activated sludge organisms than V. fischeri. The suitability of using PM6 and Shk1 for assessing wastewater toxicity on activated sludge, both individually and in a test battery, was discussed.

Biodegradation efficiency of functionally important populations selected for bioaugmentation in phenol- and oil-polluted area

Denaturing gradient gel electrophoresis of amplified fragments of genes coding for 16S rRNA and for the largest subunit of multicomponent phenol hydroxylase (LmPH) was used to monitor the behaviour and relative abundance of mixed phenol-degrading bacterial populations (Pseudomonas mendocina PC1, P. fluorescens strains PC18, PC20 and PC24) during degradation of phenolic compounds in phenolic leachate- and oil-amended microcosms. The analysis indicated that specific bacterial populations were selected in each microcosm. The naphthalene-degrading strain PC20 was the dominant degrader in oil-amended microcosms and strain PC1 in phenolic leachate microcosms. Strain PC20 was not detectable after cultivation in phenolic leachate microcosms. Mixed bacterial populations in oil-amended microcosms aggregated and formed clumps, whereas the same bacteria had a planktonic mode of growth in phenolic leachate microcosms. Colony hybridisation data with catabolic gene specific probes indicated that, in leachate microcosms, the relative proportions of bacteria having meta (PC1) and ortho (PC24) pathways for degradation of phenol and p-cresol changed alternately. The shifts in the composition of mixed population indicated that different pathways of metabolism of aromatic compounds dominated and that this process is an optimised response to the contaminants present in microcosms.

Assessing wastewater toxicity to activated sludge: recent research and developments

Toxicants in municipal sewage treatment plant (STP) influent wastewater may inhibit the biological activity of the activated sludge and cause treatment plant process upsets. Such process upsets may be avoided if influent wastewater is monitored for toxicity and protective actions are taken when toxicity is detected. A comprehensive review of the methods that can be used for assessing wastewater toxicity to biological treatment systems was conducted several years ago and the resultant report was published in 2000 by Water Environment Research Foundation (WERF). The WERF report also specified the criteria for influent wastewater toxicity monitoring methods and suggested research needs to be addressed. A significant amount of effort was made since the publication of the WERF report to develop new assays or devices and to improve existing ones. In this manuscript, recent research and developments in methods for assessing wastewater toxicity to activated sludge were reviewed. The literature indicates that bioluminescence- and respirometry-based methods received much attention in recent research. A comparison of the new/improved methods with the criteria described in the WERF report reveals that none of these methods has been shown to meet all the specified criteria. The present review also indicates that research efforts since 2000 have not fully taken into account the criteria for influent wastewater toxicity monitoring methods and have not addressed the research needs proposed in the WERF report.

Methods evaluating vanadium tolerance in bacteria isolated from crude oil contaminated land

Investigations into bacterial responses to vanadium are rare, and in this study were initiated by isolating cultures from crude oil contaminated soil from Russia and Saudi Arabia. Addition of vanadyl sulphate and vanadium pentoxide created acid conditions in the media whilst sodium metavanadate and sodium orthovanadate produced neutral and alkaline effects, respectively. Buffers were introduced for wider comparison of the sample set treatments and to distinguish between the effects of pH and compound toxicity. This study has resulted in the creation of protocols for the pH stabilisation of media containing vanadium compounds and revealed that, although vanadium salts demonstrated some toxic effects, as revealed by MIC and bioluminescence decay tests, the effects were mainly due to pH rather than inherent toxicity of the metal. Capacity for sorption of vanadium to biomass was also investigated.