Chemotactic response and adaptation dynamics in Escherichia coli

TL;DR

This study investigates the dynamics of chemotactic adaptation in Escherichia coli, combining experimental fluorescence measurements with a new dynamic model to understand how bacteria respond to chemical changes.

Contribution

The paper introduces a comprehensive dynamic model of chemotactic adaptation that incorporates receptor cooperativity, feedback regulation, and flow effects, validated by experimental data.

Findings

Imprecise adaptation for large attractant changes

Ultrafast adaptation upon attractant removal

Experimental confirmation of model predictions

Abstract

Adaptation of the chemotaxis sensory pathway of the bacterium Escherichia coli is integral for detecting chemicals over a wide range of background concentrations, ultimately allowing cells to swim towards sources of attractant and away from repellents. Its biochemical mechanism based on methylation and demethylation of chemoreceptors has long been known. Despite the importance of adaptation for cell memory and behavior, the dynamics of adaptation are difficult to reconcile with current models of precise adaptation. Here, we follow time courses of signaling in response to concentration step changes of attractant using in vivo fluorescence resonance energy transfer measurements. Specifically, we use a condensed representation of adaptation time courses for efficient evaluation of different adaptation models. To quantitatively explain the data, we finally develop a dynamic model for signaling and adaptation based on the attractant flow in the experiment, signaling by cooperative receptor complexes, and multiple layers of feedback regulation for adaptation. We experimentally confirm the predicted effects of changing the enzyme-expression level and bypassing the negative feedback for demethylation. Our data analysis suggests significant imprecision in adaptation for large additions. Furthermore, our model predicts highly regulated, ultrafast adaptation in response to removal of attractant, which may be useful for fast reorientation of the cell and noise reduction in adaptation.