Adsorption, immobilization, and activity of β-glucosidase on different soil colloids

Abstract For a better understanding of enzyme stabilization and the subsequent catalytic process in a soil environment, the adsorption, immobilization, and activity of β-glucosidase on various soil colloids from a paddy soil were studied. The calculated parameters maximum adsorption capacity ( q 0 ) for fine soil colloids ranged from 169.6 to 203.7 μg mg −1 , which was higher than coarse soil colloids in the range of 81.0–94.6 μg mg −1 , but the lower adsorption affinity ( K L ) was found on fine soil colloids. The percentages of β-glucosidase desorbed from external surfaces of the coarse soil colloids (27.6–28.5%) were higher than those from the fine soil colloids (17.5–20.2%). β-Glucosidase immobilized on the coarse inorganic and organic soil colloids retained 72.4% and 69.8% of activity, respectively, which indicated the facilitated effect of soil organic matter in the inhibition of enzyme activity. The residual activity for the fine soil clay is 79–81%. After 30 days of storage at 40 °C the free β-glucosidase retained 66.2% of its initial activity, whereas the soil colloidal particle-immobilized enzyme retained 77.1–82.4% of its activity. The half-lives of free β-glucosidase appeared to be 95.9 and 50.4 days at 25 and 40 °C. Immobilization of β-glucosidase on various soil colloids enhanced the thermal stability at all temperatures, and the thermal stability was greatly affected by the affinity between the β-glucosidase molecules and the surface of soil colloidal particles. Due to the protective effect of supports, soil colloidal particle-immobilized enzymes were less sensitive to pH and temperature changes than free enzymes. Data obtained in this study are helpful for further research on the enzymatic mechanisms in carbon cycling and soil carbon storage.