A novel cyclodextrin glucanotransferase from alkaliphilic Bacillus pseudalcaliphilus 20RF: Purification and properties

A new cyclodextrin glucanotransferase (CGTase, EC 2.4.1.19) from the obligated alkaliphile Bacillus pseudalcaliphilus 20RF, isolated from Bulgarian soils, was purified up to 18-fold by ultrafiltration and starch adsorption with a recovery of 63% activity. The enzyme was a monomer with a molecular weight 70 kDa estimated by SDS-PAGE. The CGTase exhibited two pH optima at pH 6.0 and 9.0 and was optimally active at 60 °C. The enzyme could be effectively used for conversion of raw starch into cyclodextrins (CDs) in a wide pH range, from 5.0 to 10.0 and temperatures 60–70 °C. The enzyme was more heat resistant after its pretreatment in alkaline pH 9.0 at high temperatures 65–70 °C, than at pH 6.0 under the same reaction conditions. The CGTase showed a significant stability in the presence of 15 mM various metal ions and reagents after 30 min incubation at 25 °C. The purified CGTase could be used for an efficient cyclodextrin production without any additives which is of an industrial interest. The achieved high conversion of an insoluble raw commercial corn starch into cyclodextrins (47%) with production of only two types of cyclodextrins, β- and γ-CD (80%:20%) in alkaline pH 9.0, makes B. pseudalcaliphilus 20RF CGTase industrially desired for cyclodextrin manufacture.