Enhancing the activity and thermostability of thermostable β-glucosidase from a marine Aspergillus niger at high salinity

To evaluate the effect of salinity on the catalyzing ability of beta-glucosidase in the marine fungus Aspergillus niger, the thermodynamic parameters of the beta-glucosidase were investigated at different salinities. At the optimum salinity of 6% NaCl (w/v) solution, the optimum temperature and pH of the beta-glucosidase activity was 66 degrees C and 5.0, respectively. Under these conditions, the beta-glucosidase activity increased 1.46 fold. The half-life of denaturation in 6% NaCl (w/v) solution was approximately twice as long as that in NaCl free solution. The Gibb's free energy for denaturation, Delta G, was 2 kJ/mol higher in 6% NaCl (w/v) solution than in NaCl free solution. The melting point (68.51 degrees C) in 6% NaCl (w/v) solution was 1.71 degrees C higher than that (66.80 degrees C) in NaCl free solution. Similarly, the activity and thermostability of the pure beta-glucosidase increased remarkably at high salinity. The thermostable beta-glucosidase, of which the activity and the thermostability are remarkably enhanced at high salinity, is valuable for industrial hydrolyzation of cellulose in high salinity environments. (C) 2012 Elsevier Ltd. All rights reserved.