Noise characteristics of the Escherichia coli rotary motor

TL;DR

This study investigates how various sources of noise in the chemotaxis signaling pathway of E. coli influence the behavior of its rotary motor, providing insights into cellular variability and pathway optimization.

Contribution

We developed a comprehensive model of E. coli chemotaxis signaling that captures noise effects on motor behavior, offering a framework applicable to other two-component pathways.

Findings

Motor noise signatures reflect multiple signaling processes.

Cell-to-cell variation impacts motor switching behavior.

The model helps understand pathway design and noise influence.

Abstract

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. Here, 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. This 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.