Butyrate is a preferred energy source for colonic epithelial cells and is thought to play an important role in maintaining colonic health in humans. In order to investigate the diversity and stability of butyrate-producing organisms of the colonic flora, anaerobic butyrate-producing bacteria were isolated from freshly voided human fecal samples from three healthy individuals: an infant, an adult omnivore, and an adult vegetarian. A second isolation 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. Butyrate-producing isolates were grouped by 16S ribosomal DNA (rDNA) PCR-restriction fragment length polymorphism analysis. The results indicate very little overlap between the predominant ribotypes of the three subjects; furthermore, the flora of each individual changed significantly between the two isolations. Complete sequences of 16S rDNAs were determined for 24 representative strains and subjected to phylogenetic analysis. [195][196][197][198][199] 1996), with the most abundant group (10 of 24 or 42%) clustering with Eubacterium rectale, Eubacterium ramulus, and Roseburia cecicola. Fifty percent of the butyrate-producing isolates were net acetate consumers during growth, suggesting that they employ the butyryl coenzyme A-acetyl coenzyme A transferase pathway for butyrate production. In contrast, only 1% of the 239 non-butyrate-producing isolates consumed acetate.The species diversity of the predominantly anaerobic bacterial communities from the human large bowel has been the subject of both conventional and molecular microbiological investigations (31,32,46,49). These communities are believed to contribute to healthy gut function in a variety of ways, including protecting against pathogens and producing nutrients for the colonic mucosa (3,11,12,15). We still know relatively little, however, about the contributions of individual anaerobic species to colonic fermentation and to the nutrition and health of the host.Diet-derived substrates, particularly undigested fiber and starch reaching the large intestine, have major effects upon bacterial community structure and metabolism in the colon. Short-chain fatty acids (SCFA) formed by microbial fermentation have an important effect on colonic health (10, 44). Butyrate in particular has an important role in the metabolism and normal development of colonic epithelial cells and has been implicated in protection against cancer and ulcerative colitis (21). Butyrate is preferentially transported by gut epithelial cells (36), serves as a preferred energy source for colonocytes (37,43), and has been shown to exert direct effects upon gene expression in mammalian cells through histone hyperacetylation and through interaction with butyrate response elements upstream of some genes (8, 45). Production of butyrate by mixed human fecal microflora in vitro is known to be strongly influenced by the growth substrate. Starch, for example, is strongly butyrogenic, whereas other polysaccharides such...

Seven strains of Roseburia sp., Faecalibacterium prausnitzii, and Coprococcus sp. from the human gut that produce high levels of butyric acid in vitro were studied with respect to key butyrate pathway enzymes and fermentation patterns. Strains of Roseburia sp. and F. prausnitzii possessed butyryl coenzyme A (CoA):acetateCoA transferase and acetate kinase activities, but butyrate kinase activity was not detectable either in growing or in stationary-phase cultures. Although unable to use acetate as a sole source of energy, these strains showed net utilization of acetate during growth on glucose. In contrast, Coprococcus sp. strain L2-50 is a net producer of acetate and possessed detectable butyrate kinase, acetate kinase, and butyryl-CoA:acetate-CoA transferase activities. These results demonstrate that different functionally distinct groups of butyrate-producing bacteria are present in the human large intestine.

Roseburia intestinalisFive strains of butyrate-producing, anaerobic, Gram-positive bacteria were isolated from human faecal material. These strains were slightly curved rods that showed motility by means of multiple subterminal flagella. The DNA G M C content of the strains was 29-31 mol %. A detailed investigation of the phenotypic and phylogenetic characteristics of the strains revealed that they represent a novel species of anaerobic, low-GMC-content, butyrate-producing bacterium that shows net acetate utilization during growth on media containing carbohydrates and short-chain fatty acids. The 16S rRNA gene sequences of the five isolates were determined and they confirmed that these strains were closely related to each other. Phylogenetic analysis indicated that the most closely related species are Eubacterium rectale, Eubacterium oxidoreducens and Roseburia cecicola, members of cluster XIVa of the Clostridium subphylum of Gram-positive bacteria, although they share less than 95 % sequence identity with the novel strains. It is proposed that a novel species, Roseburia intestinalis sp. nov., be created, with strain L1-82 T ( l DSM 14610 T l NCIMB 13810 T ) as the type strain.