Lecturer:   Jaime Lopez, Princeton University
Abstract:
Cross-feeding, the exchange of metabolites between organisms, is ubiquitous in the microbial world. Despite its importance in natural and engineered microbial systems, our understanding of how this metabolite exchange arises is incomplete, with existing theories limited to specific scenarios. Here, we introduce two novel mechanisms for the emergence of cross-feeding in microbial populations. The first mechanism, which we term noise-averaging cooperation (NAC), posits that noise in intracellular metabolism can promote cross-feeding. NAC is based on the idea that, due to their small size, bacteria are prone to noisy regulation of metabolism which limits their growth rate. To compensate, related bacteria can share metabolites with each other to “average out” noise and improve their collective growth. We show this mechanism can be beneficial in a simple ecological model and develop a generalized framework for predicting whether real bacteria can benefit from NAC. The second mechanism we propose is based on intracellular metabolite toxicity. In excess, the intracellular metabolites that cells require for metabolism can be detrimental to growth (e.g. due to osmotic stress). We show that such toxicity can lead to evolutionarily stable consortia of cross-feeding microbes with non-trivial population dynamics, such as a discontinuity in population size at the cross-feeding transition.