| dc.description.abstract | Chemotaxis is the ability of cells to sense their chemical environment and adjust their movement accordingly. In Escherichia coli, it has been extensively studied and has become a paradigm for signal transduction in biology. Despite its simplicity, it possesses many interesting network phenomena, most notably cooperative signal amplification and precise adaptation via a negative feedback. A fluorescence microscopy technique, Förster Resonance Energy Transfer (FRET), has proven to be a very effective experimental tool in characterizing the transfer functions of the signalling pathway in ensemble averaged measurements. While these functions provide a useful coarse-grained description in considering functional aspects, many open questions remain on the underlying molecular and cellular mechanisms. Therefore, we tailored the FRET technique to application at the single-cell level. We used this technique to characterise two different E. coli genotypes. First, in wild-type E. coli cells we measured the steady state kinase activity as well as the adaptation time scales to both repellent and attractant response. These parameters revealed earlier unnoticed differences between individual bacterial cells. Second, in E. coli cells lacking the genes necessary for adaptation we described the transfer functions of the receptor-ligand binding for individual cells. Counter-intuitively, we found that the parameters of the function describing this response varied significantly from cell to cell. This work forms a solid foundation for further investigations into cellular non-genetic variability in order to relate it to (i) heterogeneity of the motile behaviour of bacteria and (ii) differences in structural properties of cells. | |
