Isolation and basic characterization of a beta-glucosidase from a strain of Lactobacillus brevis isolated from a malolactic starter culture.

To study glycosidase activities of a Lactobacillus brevis strain and to isolate an intracellular beta-glucosidase from this strain. Lactic acid bacteria (LAB) isolated from a commercially available starter culture preparation for malolactic fermentation were tested for beta-glycosidase activities. A strain of Lact. brevis showing high intracellular beta-D-glucosidase, beta-D-xylosidase and alpha-L-arabinosidase activities was selected for purification and characterization of its beta-glucosidase. The pure glucosidase from Lact. brevis has also side activities of xylosidase, arabinosidase and cellobiosidase. It is a homotetramer of 330 kDa and has an isoelectric point at pH 3.5. The K(m) for p-nitrophenyl-beta-D-glucopyranoside and p-nitrophenyl-beta-D-xylopyranoside is 0.22 and 1.14 mmol l(-1), respectively. The beta-glucosidase activity was strongly inhibited by gluconic acid delta-lactone, partially by glucose and gluconate, but not by fructose. Ethanol and methanol were found to increase the activity up to twofold. The free enzyme was stable at pH 7.0 (t(1/2) = 50 day) but not at pH 4.0 (t(1/2) = 4 days). The beta-glucosidase from Lact. brevis is widely different to that characterized from Lactobacillus casei (Coulon et al. 1998) and Lactobacillus plantarum (Sestelo et al. 2004). The high tolerance to fructose and ethanol, the low inhibitory effect of glucose on the enzyme activity and the good long-term stability could be of great interest for the release of aroma compounds during winemaking. Although the release of aroma compounds by LAB has been demonstrated by several authors, little information exists on the responsible enzymes. This study contains the first characterization of an intracellular beta-glucosidase isolated from a wine-related strain of Lact. brevis.