Drift and behavior of E. coli cells

TL;DR

This study investigates E. coli chemotaxis in steep gradients, revealing limits in drift velocity and a novel cell pinning phenomenon, combining simulations and microfluidic experiments.

Contribution

It provides new insights into E. coli behavior in steep gradients, highlighting limitations of existing theories and discovering cell pinning due to methylation site exhaustion.

Findings

Maximal drift velocities are limited in steep gradients.

Cells can become pinned at certain attractant concentrations.

Experimental validation confirms simulation predictions.

Abstract

Chemotaxis of the bacterium Escherichia coli is well understood in shallow chemical gradients, but its swimming behavior remains difficult to interpret in steep gradients. By focusing on single-cell trajectories from simulations, we investigated the dependence of the chemotactic drift velocity on attractant concentration in an exponential gradient. While maxima of the average drift velocity can be interpreted within analytical linear-response theory of chemotaxis in shallow gradients, limits in drift due to steep gradients and finite number of receptor-methylation sites for adaptation go beyond perturbation theory. For instance, we found a surprising pinning of the cells to the concentration in the gradient at which cells run out of methylation sites. To validate the positions of maximal drift, we recorded single-cell trajectories in carefully designed chemical gradients using microfluidics.