Whole cell biosensors are the focus of considerable and increasing interest worldwide as methods for detecting and quantifying environmental toxicity, including biochemical oxygen demand (BOD), heavy ...metals, antibiotics, pesticides and herbicides. This review follows the development of whole cell biosensors from attempts to utilise changes in cellular metabolism to determine BOD and general toxicity, through the exploitation of unique metabolic pathways to detect specific toxicants, to the increasingly widespread use of genetic engineering to build new, and modify existing, sensing pathways.
The measured response of rapid biochemical oxygen demand (BOD) biosensors is often not identical to those measured using the conventional 5-day BOD assay. This paper highlights the efficacy of using ...both glucose-glutamic acid (GGA) and Organisation for Economic Cooperation and Development (OECD) BOD standards as a rapid screen for microorganisms most likely to reliably predict real effluent BODs when used in rapid BOD devices. Using these two synthetic BOD standards, a microorganism was identified that produced comparable BOD response profiles for two assays, the MICREDOX® assay and the conventional 5-day BOD₅ test. A factorial experimental design systematically evaluated the impact of four factors (microbial strain, growth media composition, media strength, and microbial growth phase) on the BOD response profiles using GGA and OECD synthetic standard substrates. An outlier was identified that showed an improved correlation between the MICREDOX® BOD (BODsens) and BOD₅ assays for both the synthetic standards and for real wastewater samples. Microbial strain was the dominant factor influencing BODsens values, with Arthrobacter globiformis single cultures clearly demonstrating superior rapid BODsens response profiles for both synthetic and real waste samples. It was the only microorganism to approach the BOD₅ response for the OECD substrate (171 mg O₂ L⁻¹), and also reported BOD values for real waste samples that were comparable to those produced by the BOD₅ test, including discriminating between filtered and unfiltered samples.
Celotno besedilo
Dostopno za:
CEKLJ, DOBA, EMUNI, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK
While direct toxicity assessment (DTA) is now widely recognised as a useful tool for environmental risk assessment, many existing tests fail to meet end-user needs. This article describes the ...significant progress made to the MICREDOX® DTA assay, developed at Lincoln Ventures Ltd, brought about by miniaturising this assay to a multi-well plate format combined with limiting current microelectrode transduction. The benefits have been reduced: preparation time, reduced assay time, lower material costs and a higher level of replication achieved. To validate the precision of the miniaturised format, the concentrations required to cause a 50% decrease in signal (EC
50
) by an archetypal group of toxicants, the chlorophenols, were determined using two terrestrial bacterial strains, Escherichia coli K12 and Klebsiella oxytoca 13183. The assay time was then reduced by stepwise adjustment of the incubation time, from 60 down to 5 min, and the EC
50
s reported by E. coli to each of the toxicants after 45, 30, 15 and 5 min incubations were determined. The results obtained match closely with those reported by the Activated Sludge Respiration Inhibition Test and confirm the miniaturised multi-well plate MICREDOX® DTA assay reliably reports representative EC
50
values for these toxicants. The previously described trends of increasing toxicity with increasing chlorine substitution and the observation that meta-substituted chlorophenols are more toxic than their ortho-substituted counterparts are also confirmed. The ability to monitor toxicity using terrestrial organisms, in volumes amenable to multi-well microtitre plates and incubations requiring only a few minutes, facilitates the rapid generation of highly reproducible, easy to operate and inexpensive DTA measurements.
Two different bacteria gave different respiratory responses to the test analytes, tributyl tin (TBT) and cadmium as expressed by positive sigmoid responses by Halomonas sp. (slope, +1.71 TBT; +1.76 ...Cd) and negative sigmoid responses by Bacillus pumilis (slope, −1.06 TBT; −0.59 Cd). The EC50 values determined from Hill plots for the response of Halomonas sp. to the TBT and Cd were 1 and 8.5mM, respectively, which were lower by a factor of 10 than the corresponding values for B. pumilis. With protoplasts of B. pumilis there was a major shift in the signal from sigmoid negative to positive with TBT (+1.35) but not Cd (−0.5), while the signals with the remaining protoplast–analyte combinations remained unchanged. For all four protoplast–analyte combinations the EC50 values were in the order of 10–100-fold lower than those for their whole cell counterparts. When other analytes were tested the protoplasts gave a similar response to tin as for TBT, but detected copper and 2,4-dichlorophenol with similar signal profiles to Cd and with lower sensitivity. The difference in signal and higher sensitivity of the two species protoplast system towards TBT/tin compared to the other analytes tested, suggests that it may feasible to develop this approach for the detection of tin residues.
Environmental and process control applications have needs for sensors that operate continuously or repeatedly, making them applicable to batch measurement and flowing product stream measurement. ...Additionally, for lactose monitoring in dairy-processing plants, the sensors must have sufficient flexibility to handle a wide range of substrate concentration and be resilient to withstand wide pH excursions brought about by frequent exposure to clean-in-place chemicals that happen without any warning. This paper describes the development and trialling of an at-line lactose biosensor that meets the needs of the dairy industry for loss monitoring of lactose in dairy-processing plants by the combination of a third-generation enzyme biosensor with a sequential injection analyser. Results, both from grab sample analysis and an at-line factory prototype, are shown from their operation when installed at a Fonterra dairy factory (New Zealand) during the 2011–2012 season. Previous sensor fabrication methods were converted to a single-step process, and the flow-through cell was adapted to bubble-free operation. The lactose concentration in wastewater-processing streams was successfully monitored by taking and analysing samples every 2–3 min, semi-continuously, for 3 months by an unskilled operator. The Fonterra site flushes approximately 100–300,000 L of wastewater per hour from its lactose plant. In the 2011–2012 season, the daily mean lactose content of this wastewater varied significantly, from 0.0 to 8.0 %
w
/
v
(0–233,712 μM) and equated to substantial total losses of lactose over a 6-month period. These lactose losses represent lost saleable or useable product.
The combination of electrochemical, optical, acoustical and other measurement techniques with the specificity of biological recognition systems has resulted in a range of new analytical devices known ...as biosensors. Biosensors are under intensive development worldwide because they have a multitude of potential applications, in particular, clinical medicine, environmental monitoring and process control of industrial processes. Their basic principles, mode of operation, performance requirements and current trends will be reviewed. A brief description of a novel biosensor developed at Lincoln Technology, the MICREDOX method, is outlined and applications for rapid measurement of biochemical oxygen demand and toxicity measurements are described. Preliminary data obtained using the MICREDOX method are reported for three standard toxic materials, zinc sulphate, 3, 5-dichlorophenol and sodium lauryl sulphate.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Direct toxicity assessment (DTA) techniques seek to measure the impact of toxic chemicals on biological materials resident in the environment. This study features the use of freeze-dried bacterial ...cells in combination with a rapid DTA analyser, SciTOX™. The effects of three factors—cryoprotectant type, bacterial strain, and storage temperature—were tested in order to validate the shelf life of the freeze-dried cells. Three freeze-dried Gram-negative bacterial strains, Acinetobacter calcoaceticus, Escherichia coli and Pseudomonas putida, were tested by using the bacteria in the SciTox™ DTA assay and recording their responses to two standard toxicants: 2,4-dicholorophenol and 3,5-dichlorophenol. Each freeze-dried strain of bacteria was prepared in two forms—either pre-treatment with polyethylene glycol (PEG) or with sucrose/Tween 80—prior to storing at either 4 or −20 °C for three different storage periods (1, 2 or 3 months). While the sucrose/Tween 80 pre-treated freeze-dried cells exhibited better cell viability, we concluded that PEG was a more suitable cryoprotectant for the bacteria used in the DTA assay because of EC₅₀ parity with fresh cell and zero-time freeze-dried cell assays. The results showed that freeze-dried cells, with appropriate materials and conditions, can give reproducible DTA results for up to 3 months. The availability of a biocomponent that can be activated by simple rehydration makes the deployment of this technology much easier for an end user.
Celotno besedilo
Dostopno za:
CEKLJ, DOBA, EMUNI, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK
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