Defining cаusаtiоn fоr the rоle of gut microbes in either supporting heаlth or in development of disease processes can be challenging. A new immune disorder has been identified with a potential link to the microbiome, but so far only an association has been established. Outline what in vivo model system you would use to test whether the microbiome is causally required for disease development, and to test the effects of introducing either a single microbe or a defined microbial community. Justify your choice. Describe one positive and one negative aspect of using the model system you outlined in part 1.