Coexistence of competing metabolic pathways in well-mixed populations

TL;DR

This paper introduces a resource-based model explaining how two competing metabolic strains can coexist in well-mixed populations, emphasizing the role of toxin production and resource influx in maintaining diversity.

Contribution

It presents a novel model where toxin production by an inefficient strain enables coexistence with a more efficient strain, expanding understanding beyond spatial mechanisms.

Findings

Coexistence depends on toxin effects and resource influx rates.

Resource scarcity favors the inefficient strain.

Higher resource influx promotes stable coexistence.

Abstract

Understanding why strains with different metabolic pathways that compete for a single limiting resource coexist is a challenging issue within a theoretical perspective. Previous investigations rely on mechanisms such as group or spatial structuring to achieve a stable coexistence between competing metabolic strategies. Nevertheless, coexistence has been experimentally reported even in situations where it cannot be attributed to spatial effects [Heredity {\bf 100}, 471 (2008)]. According to that study a toxin expelled by one of the strains can be responsible for the stable maintenance of the two strain types. We propose a resource-based model in which an efficient strain with a slow metabolic rate competes with a second strain type which presents a fast but inefficient metabolism. Moreover, the model assumes that the inefficient strain produces a toxin as a byproduct. This toxin affects the growth rate of both strains with different strength. Through an extensive exploration of the parameter space we determine the situations at which the coexistence of the two strains is possible. Interestingly, we observe that the resource influx rate plays a key role in the maintenance of the two strain types. In a scenario of resource scarcity the inefficient is favored, though as the resource influx rate is augmented the coexistence becomes possible and its domain is enlarged.