The effect of temperature on the sensitivity of poikilothennic cells to toxicant exposure was investigated, with particular attention to the relationship between temperature induced changes in cellular activity, and cell sensitivity to toxicants. Temperature was shown to have a significant influence on the metabolic activity and sensitivity to toxicants ofthree types ofpoikilothenns: E. coli, a consortium of cells isolated from activated sludge (ASBC), and a genetically modified bioluminescent fish cell line (BF-2Ilucl). The influence of temperature on the ASBC and BF-21/ucl cell sensitivity to toxicants appeared to be related to its effects on toxicant uptake and reactivity. However temperature induced changes in E. coli metabolic activity were shown to have a pronounced influence on its sensitivity to toxicants. The increased metabolic rate supported by higher temperatures was associated with decreases in E. coli sensitivity to narcotic toxicants as were the increases in E. coli metabolic activity that resulted from changes in respiratory substrate solution composition. Subsequent biosensor and growth assays demonstrated that E. coli responded to low concentrations of phenolic toxicants by increasing it respiration rate at the expense of growth. This suggests that the protective effect ofincreased metabolic activity at higher temperatures was related to the energetic costs of toxicant exposure. Additionally an impedance spectroscopy assay was developed and showed that 3,5-DCP caused only limited disruption ofE. coli membrane integrity. This study demonstrated for the first time that temperature effects on E. coli metabolic activity and on E. coli sensitivity to toxicants are directly linked. Further work is needed to develop a fuller understanding ofhow E. coli metabolic activity influences its sensitivity to toxicants.

This thesis reports on the combined effects of toxicants and physicochemical factors on micro-organisms. The main objective of the project was to use multi-sensing systems such as mediated and non-mediated sensor systems, growth tests and physicochemical sensors to investigate novel stressor-toxicant-assay combinations. Screen-printed, disposable, developmental-phase, physicochemical sensor constructs (conductivity and dissolved oxygen) were validated under conditions compatible with microbial bioassays, to ascertain their potential role in toxicity testing. The conductivity sensor construct could be used to indirectly inform on the osmolality of the test samples, but the dissolved oxygen sensor construct was not found to give reproducible results. The results were thought to be compromised by in-house screen-printing using a complex carbon ink formulation for the working electrode. Escherichia coli and a consortium with ammonia oxidation capacity (CAOC) were used as the test species for the bioassays. The combined effects of four inorganic salts (NaCl, NaN03, KCl and KN03) and two toxicants (3,5-DCP and HgCh) on E. coli were investigated using the CellSense™ biosensor system, Clark oxygen electrode and microtitre plate growth assays. A variety of trends were observed with each salt-toxicantbioassay combination, emphasising a need for better understanding of the assay media and factors such as bioavailability, to interpret the toxicity data. The results also suggested the importance of using multiple bioassays with varied end points, for toxicity testing. The CAOC, which was isolated from the activated sludge, was tested for physicochemical stressor and toxicant effects using the mediated biosensors. The results were very different from those obtained with E. coli, indicating that each species reacts to toxicants and changes in physicochemical factors differently. Although the full potential of disposable, physicochemical sensors, at the point of toxicity testing was not achieved, the study did investigate previously uncharacterised, combined effects of salts and toxicants on microbial cells. It highlighted the need for development of hybrid systems and also offered a route towards integration of physicochemical and biological sensing systems for simultaneous monitoring of both environmental and biological elements.