Horizontal gene transfer can help maintain the equilibrium of microbial communities

Horizontal gene transfer and species coexistence are two focal points in the study of microbial communities. Yet, the evolutionary advantage of horizontal gene transfer has not been well understood and is constantly being debated. Here we propose a simple population dynamics model based on frequency-dependent genotype interactions to evaluate the influence of horizontal gene transfer on microbial communities. In particular, we examine the structural stability of coexistence (i.e., the capability of the system to maintain species coexistence in response to small changes in parameters), as well as the robustness (defined as the maximal degree of perturbation the system can sustain around a stable coexistence steady state) of microbial communities. We find that both structural stability of coexistence and robustness of the microbial community are strongly affected by the gene transfer rate and direction. An optimal gene flux can stabilize the ecosystem, helping it recover from disturbance and maintain the species coexistence.