Understanding the Effects of Diet upon Microbial Activities Relevant to Health in the Human Large Intestine

This project has defined the roles of a number of key groups of human gut bacteria in the metabolism of dietary carbohydrates that reach the large intestine. <P> The dominant bacterial groups involved in butyrate formation in the human gut were established by isolation and molecular tracking methods, and a new family of CoA transferases was shown to catalyse the final step in butyrate formation in most butyrate-producing gut bacteria. <P> In human dietary trials, faecal populations of the Roseburia/ Eubacterium rectale group in particular correlate with faecal butyrate concentrations and respond to the content of carbohydrate in the diet. Thus the health benefits of fermentable carbohydrates could in part be due to stimulation of this newly defined group of butyrate-producing bacteria. <P> A small number of species were also found to be able to convert lactate into butyrate, and could therefore play a role in metabolic cross-feeding with the gut community. In particular, when dietary resistant starch and fructo-oligosaccharides are used as prebiotics to stimulate lactic acid producers such as Bifidobacterium spp in the gut, we have shown that this could potentially have the secondary effect of promoting butyrate production via cross-feeding of lactate, and also of partial breakdown products from the carbohydrates. <P>
Using proteomic and genomic approaches, we have been able to provide the first information on cell surface organisation of protein complexes involved in substrate attachment and enzymatic breakdown in the fibre-degrading species, Ruminoccocus flavefaciens.