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Title: Bacterial chemotaxis: sensory adaptation, noise filtering, and information transmission
Author: Claubnitzer, Diana
ISNI:       0000 0004 2700 3017
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2011
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Chemotaxis is a fundamental cellular process by which cells sense and navigate in theirenvironment. The molecular signalling pathway in the bacterium Escherichia coli is experimentallywell-characterised and, hence, ideal for quantitative analysis and modelling.Chemoreceptors sense gradients of a multitude of substances and regulate an intracellularsignalling pathway, which modulates the swimming behaviour. We studied the chemotaxispathway in E. coli (i) to quantitatively understand molecular interactions in the signallingnetwork, (ii) to gain a systems view of the workings of the pathway, including the effectsof noise generated by biomolecular reactions during signalling, and (iii) to understandgeneral design principles relevant for many sensory systems. Specifically, we investigatedthe adaptation dynamics due to covalent chemoreceptor modification, which includes numerouslayers of feedback regulation. In collaboration with an experimental group, weundertook quantitative experiments using wild-type cells and mutants for proteins involvedin adaptation using in vivo fluorescence resonance transfer (FRET). We developeda dynamical model for chemotactic signalling based on cooperative chemoreceptors andadaptation of the sensory response. This model quantitatively explains an interestingasymmetry of the response to favourable and unfavourable stimuli observed in the experiments.In a whole-pathway description, we further studied the response to controlledconcentration stimuli, as well as how fluctuations from the environment and due to intracellularsignalling affect the detection of input signals. Finally, the chemotaxis pathwayis characterised by high sensitivity, a wide dynamic range and the need for informationtransmission, properties shared with many other sensory systems. Based on FRET data,we investigated the emergence, limits and biological significance of Weber?s law which predictsthat the system detects stimuli relative to the background stimulus. Furthermore, westudied the information transmission from input concentrations into intracellular signals.We connect Weber?s law, as well as information transmission, to swimming bacteria andpredict typically encountered chemical inputs.
Supervisor: Endres, Robert ; Barahona, Mauricio Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral