Fluid flow generates bacterial conjugation hotspots by increasing the rate of shear-driven cell-cell encounters

TL;DR

This study demonstrates that fluid shear flow can significantly enhance bacterial conjugation rates by increasing cell-cell encounters, with an optimal shear rate identified, suggesting environmental fluid flow influences bacterial gene transfer hotspots.

Contribution

The paper introduces a controlled experimental method to quantify how shear flow affects bacterial conjugation, revealing an optimal shear rate for maximum transfer efficiency.

Findings

Conjugation rate peaks at an optimal shear rate of 100 1/s.

Shear flow can increase conjugation rates up to five times compared to diffusion-driven encounters.

High shear regions in natural environments may serve as hotspots for bacterial gene transfer.

Abstract

Conjugation accelerates bacterial evolution by enabling bacteria to acquire genes horizontally from their neighbors. Plasmid donors must physically encounter and connect with recipients to allow plasmid transfer, and different environments are characterized by vastly different encounter rates between cells, based on mechanisms ranging from simple diffusion to fluid flow. However, how the environment affects the conjugation rate by setting the encounter rate has been largely neglected, mostly because existing experimental setups do not allow direct control over cell encounters. Here, we describe the results of conjugation experiments in E. coli in which we systematically varied the magnitude of shear flow using a cone-and-plate rheometer to control the encounter rate. We discovered that the conjugation rate increases with shear until it peaks at an optimal shear rate (100 1/s), reaching a conjugation rate five-fold higher than the baseline set by diffusion-driven encounters. This optimum marks the transition from a regime in which shear promotes conjugation by increasing the rate of cell-cell encounters to a regime in which shear disrupts conjugation. Regions of high fluid shear are widespread in aquatic systems, in the gut of host organisms, and in soil, and our results indicate that these regions could be hotspots of bacterial conjugation in the environment.