The stability and resilience of indigenous gut microbiota in determining host-symbiont specificity

Processes of coevolution describe the relationship between mammals and their gut microbial symbionts, as these relationships are remarkably stable and specific between individual species. However, while the interactions between hosts and their co-evolved gut microbial symbionts have been observed across the majority of mammals, little is known about the ecological, environmental and molecular processes which facilitate the selection of microbial symbionts. Here we show that coevolutionary microbiota selection in the gut is determined through the connectiveness and resilience of endogenous gut microbiota. Factors affecting connectiveness and resilience may also play an essential role in excluding exogenous microbe engraftment. When germ-free (GF) mice were colonized with human microbiota (HM) and mouse microbiota (MM), we found that priority effects, host adaptive or innate immune function (Rag1-/-, MyD88-/- and IL10-/- GF mice), high-fat human-component diet, and mouse genetic background did not alter the preferential composition of the host-specific microbiota, regardless of colonization order. These results indicate that microbial symbiosis in mammals can display a high level of host specificity regardless of diet, immune system function, genetics, and priority effects. 16s and metagenomic sequencing were used to study the community structure and changes of the host-specific murine microbiota. Our findings represent a step forward understanding the high-fidelity species-specific selection of bacteria in the mammalian gut, strengthening the notion that some relationships between mammals and their microbial symbionts are highly coevolved and exclusive.