Metabolic Trade-Offs in Serial Dilution Culture

Microbial communities in nature typically exhibit a vast diversity of organisms. These observations clash with the predictions of resource-competition models, which allow only as many species as resources to coexist at steady state. One possible solution to this paradox is the idea that organisms are subject to trade-offs, which ensure no species has an absolute advantage over others. This concept was explored in the framework of a chemostat model by Posfai et al. (2017), who found that large regions of the nutrient supply space can support unlimited diversity if all organisms have the same fixed enzyme budget. However, while the chemostat provides a useful conceptual model, nutrient supply rates in nature are seldom steady. The other extreme corresponds to serial dilution or "seasonal" variation where nutrients are supplied periodically or even randomly in discrete packets. Here, we analyze how metabolic trade-offs influence diversity in such a serial dilution model. We characterize the effects of varying supply on the population dynamics, finding relationships that still permit unlimited diversity but differ qualitatively from those found in the chemostat case. We also examine connections between the chemostat and serial dilution models.