Osmotaxis in Escherichia coli through changes in motor speed

TL;DR

This study investigates how osmotic pressure changes influence E. coli motility, revealing a long-term increase in swimming speed and motor bias that could lead to bacterial accumulation, expanding understanding beyond chemotaxis.

Contribution

It demonstrates how nonspecific osmotic signals affect bacterial motility and motor behavior, providing new insights into bacterial response mechanisms beyond chemotaxis.

Findings

Long-term increase in swimming and motor speeds with osmotic shock

Motor bias scales with osmotic shock magnitude

Potential for bacterial accumulation due to speed changes

Abstract

Bacterial motility, and in particular repulsion or attraction towards specific chemicals, has been a subject of investigation for over 100 years, resulting in detailed understanding of bacterial chemotaxis and the corresponding sensory network in many bacterial species. For Escherichia coli most of the current understanding comes from the experiments with low levels of chemotactically-active ligands. However, chemotactically-inactive chemical species at concentrations found in the human gastrointestinal tract produce significant changes in E. coli's osmotic pressure, and have been shown to lead to taxis. To understand how these nonspecific physical signals influence motility, we look at the response of individual bacterial flagellar motors under step-wise changes in external osmolarity. We combine these measurements with a population swimming assay under the same conditions. Unlike for chemotactic response, a long-term increase in swimming/motor speeds is observed, and in the motor rotational bias, both of which scale with the osmotic shock magnitude. We discuss how the speed changes we observe can lead to steady state bacterial accumulation.