What can make a microbial community robust?

Multi-species microbial communities can perform useful functions (e.g. probiotics). For a microbial community to be useful, it must be “robust” – able to survive perturbations. Due to the complexity of microbial communities, current investigations are limited to being phenomenological or theoretical.

To gain mechanistic insights into community robustness, we will examine the robustness of a simplified engineered yeast community “CoSMO” (Cooperation that is Synthetic and Mutually Obligatory). CoSMO comprises two cooperating S. cerevisiae strains, each overproducing and releasing an essential metabolite to support the growth of the partner strain. We have constructed a mathematical model that quantitatively explains two types of community robustness: robustness against drastic population reductions (mimicking antibiotic treatments), and robustness against gentle dilutions (mimicking daily stool passage). During evolution via serial passaging of CoSMO, robustness against drastic dilutions rapidly improved in all communities, while robustness against gentle dilutions improved in some communities but declined in others. This suggests that these two types of robustness are impacted by distinct evolutionary mechanisms.

We will use the mathematical model to predict how phenotypic changes in mutant strains may impact community robustness, and experimentally test model predictions.