Characterization of a heat-active archaeal β-glucosidase from a hydrothermal spring metagenome

• A thermostable archaeal β-glucosidase was recovered from a hot spring metagenome.
• The enzyme showed optimal activity at 90 °C with 40% activity at 105 °C.
• Pressure increased the stability of the highly active Bgl1 up to 7-fold at 90 °C.
• The presence of aluminum chloride enhanced the catalytic performance.

Thermostable enzymes are required for application in a wide range of harsh industrial processes. High stability and activity at elevated temperatures, as well as high tolerances toward various reagents and solvents, are needed. In this work, a glycoside hydrolase family 1 β-glucosidase (Bgl1) of archaeal origin was isolated from a hydrothermal spring metagenome. The enzyme showed a broad substrate spectrum with activity toward cellobiose, cellotriose and lactose. Compared to most enzymes, extremely high specific activity with 3195 U/mg was observed at 90 °C and pH 6.5. Bgl1 was completely stable at pH 4.5–9.5 for 48 h at 4 °C. More than 40% of activity was measured at 105 °C. A thermal activation was observed at 90 °C after 30 min. Enzyme stability was enhanced (5- and 7-fold) after applying pressure of 100 and 200 bar at 90 °C for 2 h, respectively. The affinity of the β-glucosidase to its substrate was significantly increased in the presence of AlCl3. The Ki value for glucose was 150 mM. These distinctive characteristics distinguish Bgl1 from other enzymes described so far and make this enzyme suitable for application in numerous processes that run at high temperatures.