Microbial competition reduces metabolic interaction distances to the low μm-range

Metabolic interactions between cells affect microbial community compositions and hence their function in ecosystems. It is well-known that under competition for the exchanged metabolite, concentration gradients constrain the distances over which interactions can occur. However, interaction distances are typically quantified in two-dimensional systems or without accounting for competition or other metabolite-removal, conditions which may not very often match natural ecosystems. We here analyze the impact of cell-to-cell distance on unidirectional cross-feeding in a three-dimensional aqueous system with competition for the exchanged metabolite. Effective interaction distances were computed with a reaction-diffusion model and experimentally verified by growing a synthetic consortium of 1 mu m-sized metabolite producer, receiver, and competitor cells in different spatial structures. We show that receivers cannot interact with producers located on average 15 mu m away from them, as product concentration gradients flatten close to producer cells. We developed an aggregation protocol and varied the receiver cells' product affinity, to show that within producer-receiver aggregates even low-affinity receiver cells could interact with producers. These results show that competition or other metabolite-removal of a public good in a three-dimensional system reduces metabolic interaction distances to the low mu m-range, highlighting the importance of concentration gradients as physical constraint for cellular interactions.

Automated summary

Metabolic interactions between cells are influenced by the distance between cells, and in a three-dimensional system, these interactions are constrained by competition or removal of metabolites, reducing the metabolic interaction distances in the low micrometer range.