The gut microbiota of termites plays important roles in the symbiotic digestion of lignocellulose. However, the factors shaping the microbial community structure remain poorly understood. Because termites cannot be raised under axenic conditions, we established the closely related cockroach Shelfordella lateralis as a germ-free model to study microbial community assembly and host-microbe interactions. In this study, we determined the composition of the bacterial assemblages in cockroaches inoculated with the gut microbiota of termites and mice using pyrosequencing analysis of their 16S rRNA genes. Although the composition of the xenobiotic communities was influenced by the lineages present in the foreign inocula, their structure resembled that of conventional cockroaches. Bacterial taxa abundant in conventional cockroaches but rare in the foreign inocula, such as Dysgonomonas and Parabacteroides spp., were selectively enriched in the xenobiotic communities. Donor-specific taxa, such as endomicrobia or spirochete lineages restricted to the gut microbiota of termites, however, either were unable to colonize germ-free cockroaches or formed only small populations. The exposure of xenobiotic cockroaches to conventional adults restored their normal microbiota, which indicated that autochthonous lineages outcompete foreign ones. Our results provide experimental proof that the assembly of a complex gut microbiota in insects is deterministic.
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