A sennoside-hydrolyzing β-glucosidase from Bifidobacterium sp. strain SEN is inducible

Abstract

Bifidobacterium sp. strain SEN was isolated and characterized by hydrolytic conversion of sennosides to sennidins (Akao et al., Appl. Environ. Microbiol., 60, 1041 (1994)). The sennoside-hydrolyzing capacity of the strain SEN was disappeared following the addition of glucose to the media in spite of good bacterial growth and potent activity hydrolyzing p-nitrophenyl β-D-glucopyranoside (pNPG). In a fructose-containing medium, no such suppressing effect was shown. Following a 10 h incubation in 50 mM potassium phosphate buffer (pH 7.4), the sennoside-hydrolyzing activity of the bacterium increased, dose-dependently, with the addition of sennoside B. Inhibition of the substrate-induced increase in sennoside-hydrolyzing activity was observed following the addition of some antibiotics (chloramphenicol, streptomycin, and rifampicin). In particular, chloramphenicol completely inhibited the increase of sennoside-hydrolyzing activity while 38% pNPG-hydrolyzing activity remained. It is suggested that the strain SEN produces two different β-glucosidases of which the sennoside- hydrolyzing enzyme is inducible. In addition, the glucosides pNPG, esculin, salicin, or amygdalin stimulated the induction of the sennoside β- glucosidase, but less markedly than sennoside. Sennidin A or sugars (glucose, fructose, cellobiose, or maltose) did not induce the enzyme.