The enemy of my enemy is my friend: a plausible defense mechanism against antagonism in bacterial communities

In a recent work we studied an artificial bacterial community where resistant bacteria assisted sensitive bacteria in surviving in the presence of antagonistic bacteria. Typically, this behavior is attributed to lateral gene exchange. However, we identified evidence of a distinct mechanism, which operates on the principle of “the enemy of my enemy is my friend”. Here, we explore the viability of this mechanism by means of a reaction-diffusion mathematical model. Our findings suggest that this mechanism is feasible under specific circumstances, particularly when bacteria undergo significant metabolic changes at high population densities. Author summary The importance of studying the formation of bacterial communities cannot be overstated. Initially, it was believed that the environment alone determined the assembly of these communities, but recent research has demonstrated that interactions among members of the community also have a crucial impact. For instance, it has been observed in some cases that, even when susceptible bacteria are confronted with antagonism, they can survive with the aid of resistant bacteria. Lateral gene exchange is typically considered the underlying mechanism responsible for this phenomenon. However, we identified in a recent work an alternative mechanism that does not involve gene exchange but operates on the principle of “the enemy of my enemy is my friend”. Using a mathematical model, we examine the plausibility of this mechanism in a small artificial bacterial community. Our results indicate that this mechanism alone cannot account for all the experimental observations, but including the assumption that bacteria undergo significant metabolic changes at high concentrations may suffice. ### Competing Interest Statement The authors have declared no competing interest.