Microbial mutualism at a distance: the role of geometry in diffusive exchanges

TL;DR

This study models how the geometry of diffusive channels influences microbial mutualism, revealing that spatial structure can significantly affect microbial interactions in natural habitats.

Contribution

The paper introduces a mathematical model linking geometry to diffusive exchanges in microbial mutualism, validated with experimental data from an algal-bacterial co-culture.

Findings

Diffusive channel geometry critically influences mutualism success.

Counterintuitive effects of diffusion distance on microbial interactions.

Analytical and numerical solutions predict conditions for mutualism establishment.

Abstract

The exchange of diffusive metabolites is known to control the spatial patterns formed by microbial populations, as revealed by recent studies in the laboratory. However, the matrices used, such as agarose pads, lack the structured geometry of many natural microbial habitats, including in the soil or on the surfaces of plants or animals. Here we address the important question of how such geometry may control diffusive exchanges and microbial interaction. We model mathematically mutualistic interactions within a minimal unit of structure: two growing reservoirs linked by a diffusive channel through which metabolites are exchanged. The model is applied to study a synthetic mutualism, experimentally parameterised on a model algal-bacterial co-culture. Analytical and numerical solutions of the model predict conditions for the successful establishment of remote mutualisms, and how this depends, often counterintutively, on diffusion geometry. We connect our findings to understanding complex behaviour in synthetic and naturally occurring microbial communities.