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Candida albicans, a successful human pathogen, displays the phenomenon of glucoseenhanced oxidative stress resistance (Rodaki et al., 2009), which is not observed in other yeast species tested. The molecular bases of the phenomenon are not clear. It was suggested that glucose signalling might play a major role. Therefore, the impact of specific C. albicans mutations was tested to determine which of three known major glucose signalling pathways are required for glucose-enhanced oxidative stress resistance. Two major glucose signalling pathways were found to contribute to the phenomenon (the glucose repression pathway and the cAMP pathway), and a third pathway (the SRR pathway) is not essential for this response. The next step was to identify targets of these pathways that might contribute to the phenotype. First, it was tested whether known oxidative stress systems contribute to the GEXSR. The selected targets represented almost all main systems involved in redox control and ROS detoxification (catalase, superoxide dismutases, thiredoxins, and glutathione peroxidases) which seemed to contribute not significantly to the GEXSR. The exceptions to this were glutathione reductase (Glr1) and glutaredoxin (Grx2/Ttr1), inactivation of which affected manifestation of the phenomenon. This reinforced the view that the GSH/GSSG balance plays a key role in the GEXSR. Second, comparative analyses of transcriptomic profiles of C. albicans glucose- and lactategrown cells in response to oxidative stress and glucose treatment correspondingly revealed a small set of commonly up-regulated genes: UCF1, RNR22, MOH1, orf19.3302, and HSP21/orf19.822 (Enjalbert et al., 2006; Rodaki et al., 2009). Each potential GEXSR-specific gene appeared to be regulated in a distinct manner by the major glucose signalling pathways. The ectopic expression of potential GEXSR targets did not provide any experimental evidence to support their roles in this response. That might be related to inefficient expression from ACT1 promoter under the experimental conditions tested, and also caused by other effects.

Approximately 450 000 people have diabetes in Sweden today, and the number of diabetics only rises. Monitoring blood sugar several times a day is a fundamental part of managing the disease, and reducing the risks of complications. Today’s glucose monitoring devices are invasive and require small needle sticks for a measurement. Providing a painless method of monitoring the blood sugar level would relieve the lives of diabetics world-wide.   The objective of this project was to investigate the absorption spectra of aqueous glucose concentrations (100 to 5000 mg/dl) in the mid infrared region with Fourier Transform spectroscopy (FTIR), and finally implementing a hand-held monochromatic spectrometer to demonstrate a non-invasive concept. The method chosen for implementing the hand-held demo is due to the commercial availability of diodes and detectors at those wavelengths.   The results from the FTIR showed a trend among concentrations in all wavelengths, in between 1180 to 980 cm-1, specifically at 1035 cm-1, but also in the region 2920 to 2850 cm-1. The hand-held spectrometer did not register any transmittance of the glucose samples. For future implementations, 1035 cm-1 should be investigated more in-depth for a hand-held device.

The evaluation, analysis and development of an oxygen-insensitive amperometric glucose biosensor and its application in microbial batch culture are described. The biosensor consisted of a graphite foil electrode modified with glucose oxidase and 1,1'-dimethylferrocene, and operated via mediated electron transfer from the enzyme to the electrode. Initial evaluations illustrated several operating characteristics which would be expected to cause problems in continuous monitoring applications, most notably sensor instability and a progressive increase in response time. The main underlying causes of these unfavorable characteristics were identified as enzyme loss, mediator loss and substrate diffusion limitation within the electrode. As a consequence of these insights, further development of the sensor was undertaken. A number of different electrode materials and enzyme immobilization techniques were tested, resulting in the development of a novel immobilization procedure using a hexadecylamine coating to bind 'the activated carbohydrate residues of periodate-oxidized glucose oxidase. This improved the sensor lifetime and response time under continuous operation. Strategies for the reliable application of the biosensor in fermentation monitoring were evaluated. In-line flow cell and in_§itu membrane probe approaches were considered, and the latter approach was preferred: Considerable attention was devoted to optimising the design of such probes. The best design accommodated a three electrode configuration with a multiple biosensor array. It was found necessary to allow for periodic on-line calibration within the aseptically operating probe. This configuration was successfully applied on-line to monitor glucose in batch cultures of Escherichia coli.

D.Phil. (Chemistry) / Please refer to full text to view abstract

Ng Shu Wing. / Bibliography: leaves 196-216 / Thesis (M.Ph.)--Chinese University of Hong Kong, 1985