Stochastic Modeling of the Evolution of Antibiotic Production

In natural microbial ecologies, bacteria grow in diverse communities composed of multiple coexisting species. Competing over space and nutrients, these bacteria have evolved the ability to produce toxins, such as antibiotics, that inhibit or kill neighboring competitors. In return, the competitors can evolve resistance to these antibiotics, creating an evolutionary arms race of antibiotic production and resistance. Previous studies have shown that this arms race help create and maintain diversity in microbial communities. Less is known about the opposite process, that is of how population diversity affect the evolution of antibiotic production. Here, we developed a stochastic model to simulate the evolutionary arms-race between production and resistance in ecological communities with externally tunable diversity. We found that the average antibiotic production has increased dramatically with increasing diversity in the population. Following the evolution dynamics of production and resistance, we observe a pattern of production bursts followed by corresponding resistance bursts. When resistance overshoots the minimal resistance needed for survival, antibiotic production becomes disadvantageous and production rate quickly collapses. In a diverse set of competitors, the average resistance overshoots less frequently, thereby making it more likely for production to be maintained for a longer time. This result suggests that not only antibiotic production increases population diversity, but, in return, higher diversity boosts antibiotic production. This positive feedback loop can shed light on the intrinsic ecological mechanisms that lead to and maintain biodiversity in nature.