Cheaters Impart Robustness to Cooperative Yeast Populations in Changing Environments

Natural as well as synthetic microbial communities are continually subjected to changes in environmental factors such antibiotics, temperature, pH, and nutrient availability, which directly impact their composition and function. While designing robust communities that maintain their composition and functionality in fluctuating environments is highly desirable, little is known about the nature of ecological interactions that render populations robust or sensitive to environmental changes. Here, using a phenomenological model of population dynamics we show that the population size of public good producing microbes (cooperators) can be rendered insensitive to changes in mortality rate via interactions with non-producing cheaters. Furthermore, we verify this prediction experimentally by demonstrating that the population size of glucose producing yeast cells is robust with respect to changes in the dilution rate in the presence of glucose non-producing cheater cells. Remarkably, our experiments reveal that in addition to maintaining a constant co-operator population size, the presence of cheaters also suppresses the variation in glucose concentration with dilution rate.