Cyclodextringlucanotransferase of the Alkalophilic Strain Caldalkalibacillus mannanilyticus IB-OR17-B1

An extracellular cyclodextrin glucanotransferase (CGTase, EC 2.4.1.19) has been characterized for the first time in a strain of bacteria of the species Caldalkalibacillus mannanilyticus IB-OR17-B1. The enzyme was isolated from the culture supernatant using ultrafiltration and affinity adsorption on corn starch. The specific activity of the CGTase increased by 18 times as a result of purification with an enzyme yield of 56%. The molecular weight of the isolated enzyme was 70 kDa according to the denaturing electrophoresis in polyacrylamide gel. The CGTase of C. mannanilyticus IB-OR17-B1 demonstrated its maximum cyclizing activity at pH 8 and a temperature of 60°C, respectively, and it was stable in the pH range of 7–10 and temperatures of 70°C or less. The thermal stability of the enzyme under 70°C increased by 10–15% in the presence of 5–10 mM of calcium and magnesium salts. The cations of Ag⁺, Cu²⁺, Zn²⁺, Fe²⁺ and Fe³⁺ at a concentration of 5 mM inhibited CGTase activity by 90, 26, 23, 18, and 11%, respectively. Under the optimal conditions and enzyme-substrate ratio 1 U/g the isolated CGTase converted potato starch to mixture of α-, β-and γ-cyclodextrins with weight ratio 38.8 : 52.6 : 8.6 and a yield of 42% in 24 h.