Design and application of synthetic human gut microbial communities.

The gut microbiome shapes host health through a complex network driven by both host‒microbe and microbe‒microbe interactions. Disruption of these interactions, often referred to as dysbiosis, is associated with a range of infectious and chronic diseases. Owing to the success of fecal microbiota transplantation (FMT) for the treatment of recurrent Clostridioides difficile infection, FMT has been explored as a therapeutic option for a range of microbiota-associated conditions, including inflammatory bowel disease and obesity. However, the microbial diversity that is the greatest strength of FMT is also its greatest liability. Concerns relating to reliance on human donors, potential for transmission of multidrug-resistant organisms or undesirable phenotypes demonstrate a need for alternate approaches, including the generation of synthetic alternatives to FMT, which can be built in the laboratory from individual strains. Furthermore, these communities are powerful tools for conducting mechanistic research allowing for the generation of 'knockout' communities, which are not possible when working with undefined fecal transplants. This review examines strategies for designing synthetic microbial communities that represent a new generation of microbiome-derived therapies. We highlight how synthetic microbial communities are being used to answer mechanistic questions about host-microbiome interactions relevant to health and disease. Finally, we examine the current clinical translation of these communities as live biotherapeutic products (LBPs). While the regulatory frameworks for LBPs continue to evolve, early clinical successes illuminate the potential for synthetic microbial communities to treat complex human diseases through targeted manipulation and restoration of the gut microbiome.