Biochemical Characterization of a β-1,3-Glucanase from <i>Bacteroidetes</i> sp. Having Transglycosylase Activity Suitable to Synthesize β-Glucooligosaccharides

β-1,3-Glucanases have prospective applications in areas such as functional oligosaccharide preparation, plant protection, and breweries. In this study, a glycoside hydrolase (GH) family 17 β-1,3-glucanase (BbGlc17A) from <i>Bacteroidetes</i> bacterium from a microbial mat metagenome from the Great Salt Lake was identified. BbGlc17A catalyzed the hydrolytic conversion of laminarin into β-glucooligosaccharides with polymerization degrees of 3-8. The optimal catalytic conditions of BbGlc17A were pH 6.5 and 30 °C. In addition to its hydrolytic activity, BbGlc17A also exhibited transglycosidase activities, involving catalysis of the formation of new β-1,6-glycosidic bonds. BbGlc17A exhibits the classic (β/α)8 TIM-barrel structure and possesses an elongated catalytic groove, distinguishing it from other typical β-1,3-glucanases, which promote the forward direction of the transglycoside reaction. This effectively highlights the potential of the enzyme to convert β-1,3-glucan into mixed functional oligosaccharides. These results reveal the catalytic properties and the application potential of the GH family 17 β-1,3-glucanase and provide valuable information about the group of carbohydrate-active enzymes in biochemistry.