Starvation drives co-existence in cross-feeding bacterial populations

Cross-feeding is a universal feature of natural microbial communities that extends even into subpopulation structures, generating cooperative ecotypes. However, we still lack an understanding of the ecological parameters that support the ecotype co-existence necessary for co-evolution between partners within populations. Here, we show that repeated moderate starvation – conditions that mimic the fluctuations experienced by microbes in nature – can drive frequency-dependent co-existence for hundreds of generations, providing a new mechanism for the origin of cooperation and the maintenance of population-level diversity in natural microbial communities.