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Open Access Research article

Noise characteristics of the Escherichia coli rotary motor

Diana Clausznitzer123 and Robert G Endres12*

Author Affiliations

1 Division of Molecular Biosciences, Imperial College London, SW7 2AZ London, UK

2 Centre for Integrative Systems Biology and Bioinformatics, Imperial College London, UK

3 BioQuant, Universit├Ąt Heidelberg, 69120 Heidelberg, Germany

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BMC Systems Biology 2011, 5:151  doi:10.1186/1752-0509-5-151

Published: 27 September 2011



The chemotaxis pathway in the bacterium Escherichia coli allows cells to detect changes in external ligand concentration (e.g. nutrients). The pathway regulates the flagellated rotary motors and hence the cells' swimming behaviour, steering them towards more favourable environments. While the molecular components are well characterised, the motor behaviour measured by tethered cell experiments has been difficult to interpret.


We study the effects of sensing and signalling noise on the motor behaviour. Specifically, we consider fluctuations stemming from ligand concentration, receptor switching between their signalling states, adaptation, modification of proteins by phosphorylation, and motor switching between its two rotational states. We develop a model which includes all signalling steps in the pathway, and discuss a simplified version, which captures the essential features of the full model. We find that the noise characteristics of the motor contain signatures from all these processes, albeit with varying magnitudes.


Our analysis allows us to address how cell-to-cell variation affects motor behaviour and the question of optimal pathway design. A similar comprehensive analysis can be applied to other two-component signalling pathways.