Phylogenetic distribution of genes encoding β-glucuronidase activity in human colonic bacteria and the impact of diet on faecal glycosidase activities

Bacterial beta-glucuronidase in the human colon plays an important role in cleaving liver conjugates of dietary compounds and xenobiotics, while other glycosidase activities are involved in the conversion of dietary plant glycosides. Here we detected an increase in beta-glucuronidase activity in faecal samples from obese volunteers following a high-protein moderate carbohydrate weight-loss diet, compared with a weight maintenance diet, but little or no changes were observed when the type of fermentable carbohydrate was varied. Other faecal glycosidase activities showed little or no change over a fivefold range of dietary NSP intake, although a-glucosidase increased on a resistant starch-enriched diet. Two distinct groups of gene, gus and BG, have been reported to encode beta-glucuronidase activity among human colonic bacteria. Degenerate primers were designed against these genes. Overall, Firmicutes were found to account for 96% of amplified gus sequences, with three operational taxonomic units particularly abundant, whereas 59% of amplified BG sequences belonged to Bacteroidetes and 41% to Firmicutes. A similar distribution of operational taxonomic units was found in a published metagenome dataset involving a larger number of volunteers. Seven cultured isolates of human colonic bacteria that carried only the BG gene gave relatively low beta-glucuronidase activity that was not induced by 4-nitrophenyl-beta-D-glucuronide. By comparison, in three of five isolates that possessed only the gus gene, beta-glucuronidase activity was induced.