Two alpha-glucosidase encoding genes (aglA and aglB) from Bifidobacterium adolescentis DSM 20083 were isolated and characterized. Both alpha-glucosidases belong to family 13 of the glycosyl hydrolases. Recombinant AglA (EC 3.2.1.10) and AglB (EC 3.2.1.20), expressed in Escherichia coli, showed high hydrolytic activity towards isomaltose and pnp-alpha-glucoside. The K,, for pnp-alpha-glucoside was 1.05 and 0.47 mM and the V-max was 228 and 113 U mg(-1) for AglA and AglB, respectively. Using pnp-a-glucoside as substrate, the pH optimum for AglA was 6.6 and the temperature optimum was 37degreesC. For AglB, values of pH 6.8 and 47degreesC were found. AglA also showed high hydrolytic activity towards isomaltotriose and, to a lesser extent, towards trehalose. AglB has a high preference for maltose and less activity towards sucrose; minor activity was observed towards melizitose, low molecular weight dextrin, maltitol, and maltotriose. The recombinant a-glucosidases were tested for their transglucosylation activity. AglA was able to synthesize oligosaccharides from trehalose and sucrose. AglB formed oligosaccharides from sucrose, maltose, and melizitose.