Laminarinase (beta-glucanase) activity in Bacteroides from the human colon

Laminarin, a beta(1 leads to 3)-glucan similar to those found in plant cell walls, is fermented by some species of anaerobic bacteria from the human colon. Laminarinase (EC 3.2.1.6) and beta-glucosidase (EC 3.2.1.21) activities were determined in strains representing Bacteroides thetaiotaomicron, Bacteroides distasonis, and an unnamed deoxyribonucleic acid homology group of Bacteroides fragilis. In all three species, laminarinase activity was inducible by laminarin and was predominantly cell bound. The products of laminarinase activity varied with each species. In the case of B. thetaiotaomicron, the major product of laminarin hydrolysis was glucose (70 to 90%), and there were small amounts of laminaribiose (G2) and oligomers of glucose as high as G4. In the case of group '0061-1,' glucose (40 to 50%) and oligomers of glucose as high as G6 were found. The laminarinase of B. distasonis differed from the laminarinases of the other two species in that it mainly produced oligomers of glucose (G2-G5). beta-Glucosidase activity was also found in all three species. beta-Glucosidase was induced by glucose-containing disaccharides as well as by laminarin. The beta-glucosidases of the three Bacteroides species differed with respect to level of activity, induction pattern, and sensitivity to inhibition by D-glucono-1,5-lactone.