Production and characterization of a new cyclodextrin glycosyltransferase from Bacillus firmus isolated from Brazilian soil

A new CGTase was obtained from Bacillus furmus, strain 713, isolated from oat soil culture, using a high alkaline pH medium containing 1% Na2CO3. The enzyme was characterized in soluble form, for pH 5-11, temperature from 30 to 85 degrees C, using a 1% maltodextrin substrate solution and appropriate buffers. It produced mainly P-CD and the cell-free supernatant had a precipitating activity measured by the trichloroethylene method that is a 100-fold greater than that of the enzyme of Bacillus firmus, strain 37, previously studied by our group. The molecular weight of the pure protein was measured as 56,230 Da with SDS-PAGE. The optimum temperature for the enzyme activity was 50 degrees C and it was most active at pH 6.0. Thermal deactivation was noticeable above 65 degrees C and the enzyme was highly stable below 60 'C. The influence of substrate or product concentration on the initial rate of CD production was studied and the kinetic parameters were determined. The enzyme showed cyclization activity on different raw and hydrolyzed starches and hydrolyzed cornstarch gave the highest activity. (C) 2007 Elsevier Ltd. All rights reserved.