Metabolic switching promotes microbial coexistence under fluctuating resources

Resource fluctuations can facilitate microbial coexistence when species are sufficiently differentiated in their resource uptake strategies. However, past emphasis on the binary classification of species into equilibrium versus non-equilibrium resource specialists has obscured the potential range of temporal niches available to competitors. Here, we investigate whether microbes that switch between respiratory and fermentative metabolism can coexist with specialist competitors under fluctuations in a single resource. Based on simulations of consumer-resource models, we show that metabolic switching generates distinct growth responses to resource availability, allowing metabolically flexible organisms to exploit temporal variation in ways that differ from specialist strategies. As a result, metabolic switchers can coexist with both respiratory and fermentative specialists under intermediate regimes of resource fluctuation. The competitive ability of metabolic switchers is enhanced when transitions between metabolic states are faster and more responsive to changes in resource availability. Rather than constituting physiological constraints, our results suggest that the metabolic flexibility afforded by overflow metabolism may enable organisms to better exploit fluctuating resources environments.