Vice-Principal External Affairs & Dean for Europe
Figure 1: In this experiment, Pseudomonas fluorescens were engineered to express the bacterial lux operon constitutively. The flask on the left has been photographed in the light and the flask on the right has been photographed in the dark and is seen due to emission of bioluminescence. We have exploited the phenomenon of bioluminescence to create a suite of whole cell biosensors. Using lux (prokaryotic) or luc (eukaryotic) reporter genes we have constructed bacterial, single celled eukaryotic and multicellular eukaryotic biosensors. As bioluminescence is a rapid and sensitive indicator of cell metabolic activity, we can use these biosensors to detect bioactive compounds (see Fig. 1). We have applied these biosensors to investigate factors which affect the activity of bacterial cells as well as developing a rapid toxicity test which enables contamination to be detected in environmental samples such as water, soil, sediment and sludge. Increasing levels of toxicity are seen as decreasing output of bioluminescence (see Fig. 2 - courtesy of H. Weitz, University of Aberdeen). We can also apply the biosensors in a novel application to determine the bioremediation potential of contaminated land and water.
Figure 2: This figure shows the bioluminescence of a culture of lux-marked bacteria in response to an increasing concentration of toxin. We have extended this work further to construct biosensors which respond to other toxins such as paralytic shellfish toxins and are developing these as an alternative to current animal tests for these toxins. In parallel with this we are investigating the molecular biology of paralytic shellfish toxin production. Microbial Diversity We have a large programme of research focussed on the study of microbial diversity. By applying molecular technologies such as PCR amplification of 16s rDNA and DGGE analysis we are determining the scale of microbial diversity (see Fig. 3 - courtesy G. Nicol, University of Aberdeen) and we are correlating microbial diversity to the impact of plant growth, input of fertiliser and pollution. We are trying to answer questions such as: does microbial diversity matter? how quickly can microbial diversity recover after disruption? does microbial diversity have an impact on plant growth/health is microbial diversity/community structure important in the human gut to protect against disease?
Figure 3: An example of total bacterial DGGE fingerprints obtained from 8 individual 0.1 g samples from a single site. Each sample was run in duplicate. This gel indicates that, in this case, there was relatively little variation between samples. We are extending this work to estimate microbial diversity in other environments such as the human gut and to determine the role of viable but non-culturable (VBNC) bacteria in cryptic infections. Microbial Signalling Bacteria can regulate their gene expression by sensing their population density through a luxI/R regulatory system. This gives them a mechanism to signal to each other, and possibly to other bacteria which may be important in establishing microbial communities. We are investigating microbial signalling in Pseudomonas corrugata, a biocontrol agent, and have identified a luxI homologue in this bacterium. We are trying to elucidate whether a density dependant signaling mechanism is important for effective biocontrol in this bacterium. We are also developing technologies to allow us to interfere with density dependant regulation of pathogenicity genes in bacterial pathogens so that we can develop alternative antibiotics for use therapeutically.