Colonization with heterologous bacteria reprograms a Caenorhabditis elegans nutritional phenotype

Animals rely on the gut microbiome to process complex food compounds that the host cannot digest and to synthesize nutrients that the host cannot produce. New systems are needed to study how the expanded metabolic capacity provided by the gut microbiome impacts the nutritional status and health of the host. Here we colonized the nematode Caenorhabditis elegans gut with cellulolytic bacteria that enabled C. elegans to utilize cellulose, an otherwise indigestible substrate, as a carbon source. The nutritional benefits of colonization with cellulolytic bacteria were assayed directly, by incorporation of isotopic biomass, and indirectly, as host larval yield resulting from glucose release in the gut. As a community component in the worm gut, cellulolytic bacteria can also support additional bacterial species with specialized roles, which we demonstrate by using Lactobacillus to protect against Salmonella infection. As a model system, C. elegans colonized with cellulolytic bacteria can be used to study microbiome-host interactions. Engineered microbiome communities may provide host organisms with novel functions, such as the ability to use more complex nutrient sources and to fight against pathogen infections.