Chemotaxis is a fundamental cellular process by which cells sense and navigate in their
environment. The molecular signalling pathway in the bacterium Escherichia coli is experimentally
well-characterised and, hence, ideal for quantitative analysis and modelling.
Chemoreceptors sense gradients of a multitude of substances and regulate an intracellular
signalling pathway, which modulates the swimming behaviour. We studied the chemotaxis
pathway in E. coli (i) to quantitatively understand molecular interactions in the signalling
network, (ii) to gain a systems view of the workings of the pathway, including the effects
of noise generated by biomolecular reactions during signalling, and (iii) to understand
general design principles relevant for many sensory systems. Specifically, we investigated
the adaptation dynamics due to covalent chemoreceptor modification, which includes numerous
layers of feedback regulation. In collaboration with an experimental group, we
undertook quantitative experiments using wild-type cells and mutants for proteins involved
in adaptation using in vivo fluorescence resonance transfer (FRET). We developed
a dynamical model for chemotactic signalling based on cooperative chemoreceptors and
adaptation of the sensory response. This model quantitatively explains an interesting
asymmetry of the response to favourable and unfavourable stimuli observed in the experiments.
In a whole-pathway description, we further studied the response to controlled
concentration stimuli, as well as how fluctuations from the environment and due to intracellular
signalling affect the detection of input signals. Finally, the chemotaxis pathway
is characterised by high sensitivity, a wide dynamic range and the need for information
transmission, properties shared with many other sensory systems. Based on FRET data,
we investigated the emergence, limits and biological significance of Weber’s law which predicts
that the system detects stimuli relative to the background stimulus. Furthermore, we
studied the information transmission from input concentrations into intracellular signals.
We connect Weber’s law, as well as information transmission, to swimming bacteria and
predict typically encountered chemical inputs.