Potential contribution of microbial interaction to stochasticity of microbiota assembly.

Microbial interaction has been widely acknowledged as the deterministic factor for microbiota assembly. However, in the microbial environment, such interactions are highly variable and may lead to the random birth, death, and reproduction of neighboring microbes, potentially contributing to stochastic assembly processes. We have developed a Go-board model to simulate and investigate how microbiota assembly is affected by different types of interacting species, interaction strength, and community structure. The infer Community Assembly Mechanisms by Phylogenetic-bin-based null model analysis (iCAMP) shows that the strong inhibitory effect of deterministic species on stochastic species can lead to a switch of the dominant assembly process from heterogeneous selection to drift. On the other hand, the effects of the inhibition of stochastic species on their deterministic neighbors enhances the relative importance of dispersal limitation in communities with small deterministic populations. The mutual inhibition between deterministic and stochastic species further enhances the stochasticity of microbiota assembly, but this effect is canceled out by the effects of interspecific facilitation and deterministic species with large phylogenetic distance. Our study sheds novel light on the role of microbial interaction in stochastic assembly processes, which is contradictory to the traditional niche-based theory. These findings highlight the importance of assessing interspecific interaction for predicting the true roles of different assembly processes in future studies.