Abstract

Regions of the mammalian gut harbour dense microbial communities that derive most of their energy from the anaerobic breakdown of dietary carbohydrates that are not digested by host enzymes. Especially in herbivores, the organic acids produced by microbial fermentation in turn provide a major supply of energy for the host, while in the human colon they have an important impact on health. It is of key interest therefore to understand how the microbial communities of the rumen and human large intestine respond to dietary change and how this affects the production of alternative metabolic products. While some metabolic and degradative capabilities are widespread among the microbiota, many (eg. methanogenesis, degradation of crystalline cellulose, lactate utilization) appear to be restricted to a small number of phylogenetic groups. Information from cultured isolates, defined consortia, experimental models, metagenomics and in vivo studies is helping to define functional group s of human gut bacteria whose characteristics can be incorporated into theoretical models that explore inter-group interactions and community responses.