Lactobacillus san franciscensis CB1 uses cellobiose and other beta-glucosides (methyl-beta beta-glucoside, arbutin, amygdalin and salicin) as carbon sources. A hexameric ca. 288 kDa beta-glucosidase was purified to homogeneity from Lact. sanfranciscensis CB1 by four chromatographic steps. The enzyme was optimally active at pH 7.5 and 40 degrees C. It had a pI of ca. 4.38 and a D-55 degrees C value of ca. 27 sec. Almost total inhibition was found with sulfhydryl-modifying agents and divalent cations such as Cu2+, Co2+, Hg2+, Ni2+ and Fe2+ at a concentration of 2 mM. The enzyme was active towards beta-(1 -> 4) substrates such as p-nitrophenyl-beta-D-glucoside, -D-galactoside and -L-rhamnoside, and cellobiose. The sequencing of four internal peptides showed an elevated identity with other bacterial P-glucosides of family 3. A PCR strategy with primers designed on the basis of conserved sequences was used to partially identify the gene. The deduced amino acid sequence showed 53, 48 and 45% identity with GHF3 from Ruminococcus albus, Clostridium thermocellum and Bifidobacterium longum, respectively.