Phylogenetic relationships of butyrate-producing bacteria from the human gut

Butyrate is a preferred energy source for colonic epithelial cells and is t hought to play an important role in maintaining colonic health in humans. I n order to investigate the diversity and stability of butyrate-producing or ganisms of the colonic flora, anaerobic butyrate-producing bacteria were is olated from freshly voided human fecal samples from three healthy individua ls: an infant, an adult omnivore, and an adult vegetarian. A second isolati on was performed on the same three individuals 1 year later. Of a total of 313 bacterial isolates, 74 produced more than 2 mM butyrate in vitro. Butyr ate-producing isolates were grouped by 16S ribosomal DNA (rDNA) PCR-restric tion fragment length polymorphism analysis. The results indicate very littl e overlap between the predominant ribotypes of the three subjects; furtherm ore, the flora of each individual changed significantly between the two iso lations, Complete sequences of 16S rDNAs were determined fur 24 representat ive strains and subjected to phylogenetic analysis, Eighty percent of the b utyrate-producing isolates fell within the XIVa cluster of gram-positive ba cteria as defined by M. D. Collins et at. (Int. J. Syst. Bacteriol. 44:812- 826, 1994) and A. Willems et al. (Int. J. Syst. Bacterial. 46:195-199, 1996 ), with the most abundant group (10 of 24 or 42%) clustering with Eubacteri um rectale, Eubacterium ramulus, and Roseburia cecicola, Fifty percent of t he butyrate-producing isolates were net acetate consumers during growth, su ggesting that they employ the butyryl coenzyme A-acetyl coenzyme A transfer ase pathway for butyrate production, In contrast, only 1% of the 239 non-bu tyrate-producing isolates consumed acetate.