A three-strain synthetic community model whose rapid response to antagonism allows the study of higher-order dynamics and emergent properties in minutes

A fundamental question in the assembly of microbial communities is how complex systems arise from a few components. Synthetic communities allow addressing the dynamics and mechanisms of complex microbial interactions. Most studies on microbial interactions are done in lapses of hours and even days, but microbes must be able to sense danger in seconds. We assembled a three-strain synthetic community from the phylum Bacillota that, based on previously evaluated paired interactions, appear to have different ecological roles: resistant (R), antagonists (A), and sensitive (S). The BARS synthetic community ( Bacillota A + S + R) reproduces features of complex communities and exhibits higher-order interaction dynamics. The majority of the S strain population, Sutclifiella horikoshii 20a, dies within 5 min in a paired interaction with A strain, Bacillus pumilus 145. An emergent property appears upon adding the third interactor, as antagonism of strain A over S is not observed in the presence of the R strain, Bacillus cereus 111. After the first five min a change of state of the cells is observed, as the surviving population of the S strain seemed to have acquired tolerance to A. In summary, our model allows the study of the assembly dynamics of a three-species community and to evaluate the immediate outcome within a 30 min frame. The BARS has features of a complex system where the paired interactions do not predict the community dynamics. The model is amenable to mechanistic dissection and to modeling how the parts integrate to achieve collective properties. IMPORTANCE Microbial communities are of utmost importance, given their roles in health, agriculture, and all biogeochemical cycles on Earth. Synthetic ecology studies communities by reducing the number of variables. Microbial interactions are usually evaluated in hours or days, however, upon a first encounter, bacteria must respond in minutes, particularly when competition involves killing of neighboring cells. We generated a synthetic community of three species that allows the study of community dynamics in a 30 min frame. We denominated our model BARS as it comprises Bacillota strains that in paired interactions are Antagonist, Resistant, or Sensitive. Even though in paired interaction the antagonist kills the sensitive strain, in a triple interaction, the resistant strain provides stability to the community by neutralizing the antagonism. Therefore, BARS is a rapid response model with features of a complex system where the paired interactions do not predict the community dynamics and exhibit emergent properties. ### Competing Interest Statement The authors have declared no competing interest.