We previously reported that the oligosaccharide chains of hog gastric mucin were degraded by unidentified subpopulations numbering 1% of normal human fecal bacteria. Here we report on the enzyme-producing properties of five strains of mucin oligosaccharide chain-degrading bacteria isolated from feces of four healthy subjects. Four were isolated from the greatest fecal dilutions yielding mucin side chain-degrading activity in culture, and thus were the numerically dominant side chain-degrading bacteria in their respective hosts. Three were Ruminococcus strains and two were Bifidobacterium strains. Two Ruminococcus torques strains, IX-70 and VIII-239, produced blood group A-and H-degrading a-glycosidase activities, sialidase, and the requisite jl-glycosidases; these strains released >90% of the anthrone-reacting hexoses from hog gastric mucin during growth in culture. The Bifidobacterium strains lacked A-degrading activity but were otherwise similar, these released 60-80% of the anthrone-reacting hexoses but not the A antigenic structures from hog gastric mucin. Only Ruminococcus AB strain VI-268 produced blood group B-degrading a-galactosidase activity, but this strain lacked ,5-N-acetyl exosaminidases to complete degradation of B antigenic chains. When this strain was co-cultured with a strain that produced jl-N-acetylhexosaminidases, release of hexoses from blood group B salivary glycoprotein increased from 50 to >90%, and bacterial growth was enhanced. The glycosidases required for side chain degradation were produced by these strains in the absence of mucin substrate, and a substantial fraction of each activity in stationary phase cultures was extracellular. In contrast, none of 16 other fecal Bacteroides, Escherichia coli, Streptococcus faecalis, and Bifidobacterium strains produced ABH blood group-degrading enzymes; other glycosidases produced by these strains were predominantly cell bound except for extracellular j-N-acetylhexosaminidases produced by the five S. faecalis strains.We conclude that certain Bifidobacterium and Ruminococcus strains are numerically dominant populations degrading mucin oligosaccharides in the human colon due to their constitutive production of the requisite extracellular glycosidases including blood group antigen-specific a-glycosidases. These properties characterize them as a functionally distinct subpopulation of normal human enteric microflora comprised of An abstract of portions of this work was published in Gastroenterology 1983; 84:1191.

A B S T R A C T Recent work indicates that subpopulations of human fecal bacteria, averaging -1% of the total viable fecal flora, degrade the oligosaccharide side chains of hog gastric mucin, which structurally resembles human epithelial mucins. Here we report studies to determine whether degradation of mucin oligosaccharides is related to glycosidase production by bacteria growing in anaerobic fecal cultures. Triplicate cultures containing hog gastric mucin were inoculated with serially diluted feces from each of seven healthy subjects. When the stationary growth phase was attained, mucin oligosaccharide degradation and both cell-bound and extracellular activities of four glycosidases were measured in each culture. Cell-bound,j-D-galactosidase, ,B-N-acetylglucosaminidase, and sialidase were present in bacteria growing at all levels of fecal inocula, including 10-'1 g. In contrast, extracellular activities were present in every culture inoculated with 10-4-10-7 g feces, but were diminished or absent in cultures inoculated with 10-8_ 10-11 g feces.Bacterial autolysis was an unlikely cause of extracellular glycosidase activity, since p-nitrophenyl-a-Lfucosidase remained cell bound in cultures at every level of fecal inoculum. Degradation of mucin oligosaccharides was associated with extracellular, but not with cell-bound f3-D-galactosidase, 18-N-acetylglucosaminidase, and sialidase. Among the seven subjects, the estimated most probable numbers (MPN) of fecal bacteria producing extracellular 8-D-galactosidase, f8-N-acetylglucosaminidase, and sialidase ranged from 106_ 1010/g dry fecal wt, were comparable to the MPN of mucin-degrading bacteria, and were significantly smaller than the MPN of total fecal bacteria.Received for publication 30 June 1980 and in revised form 19 September 1980. We interpret these findings as evidence for the existence of bacterial subpopulations in the normal fecal flora that produce extracellular glycosidases, and that these subpopulations have a major role in degrading the complex oligosaccharides of mucin in the gut lumen.

A B S T R A C T Human feces contain enzymes producedby enteric bacteria that degrade the A, B, and H blood group antigens of gut mucin glycoproteins. We have studied their production in fecal cultures to determine if such cultures can be a source for enzyme purification and to explore how blood group antigen-degrading enzymes are adapted in individual human colon ecosystems. They were present in fecal cultures from each of 27 healthy subjects, including ABH nonsecretors. Heatsensitive obligate anaerobes are their major source. From 39 to 85% of the total enzyme activity produced by growing cultures was extracellular. Commercial hog gastric mucin and salivary glycoproteins, including Le' saliva which lacks A, B, and H antigens, enhance production of A-, B-, and H-degrading activity in anaerobic fecal cultures irrespective of the glycoprotein's blood group specificity. There is evidence that the host's ABO blood type and secretor status affects the specificity of blood group-degrading enzymes produced by his fecal bacteria in vitro. Thus, fecal inocula from B secretors incubated with hog gastric mucin (A and H specificity) or with Lea saliva produced greater levels of B-degrading than A-or H-degrading activity, and inocula from A secretors in similar media produced greater levels of A-degrading than B-or H-degrading activity. Blood group-degrading enzymes produced in fecal cultures are glycosidases and not proteases. The B-degrading enzyme cleaves the B antigenic determinant a-D-galactose A portion of this work was presented in abstract form in 1972. Clin. Res. 20: 728.

To cleave blood group A immunodeterminants from erythrocytes (Hoskins, L. C., Larson, G., and Naff, G. B. (1995) Transfusion 35, 813-821), we purified and characterized ␣-N-acetylgalactosaminidase (EC 3.2.1.49) activity from culture supernatants of the human fecal bacterium Ruminococcus torques strain IX-70. Three isoforms separated during hydrophobic interaction chromatography. Hydroxyapatite chromatography further resolved the most hydrophilic, isoform I, into isoforms IA and IB. The most hydrophobic, isoform III, differed from IA and IB by a more acidic pH optimum, greater heat resistance, greater sensitivity to alkylating agents, and anomalous retardation during gel filtration chromatography. Isoform IB differed from IA and III in N-terminal amino acid sequence and in sensitivity to EDTA inhibition. Each cleaved nonreducing ␣(133)-N-acetylgalactosamine residues from human blood group A and AB mucin glycoproteins, Forssman hapten, and blood group A lacto series glycolipids. The apparent molecular mass of denatured isoform subunits of IA, IB, and III-PII (158, 173, and 201 kDa, respectively) bore no integer relationship to the apparent molecular mass of the native isoforms (265, 417, and 530 kDa), but the latter bore a ratio of 1.96:3.09:3.93 to the weight-average apparent molecular mass of native IA (135 kDa), suggesting that the isoforms are multimers of a 135-kDa sequence. Isoforms IA and III-PII had an identical N-terminal amino acid sequence which showed homologies to the N-terminal sequence of sialidases produced by Bacteroides fragilis SBT3182, another commensal enteric bacterium.