6-Alpha-glucosyltransferase and 3-alpha-isomaltosyltransferase from Bacillus globisporus N75.

A bacterial strain, Bacillus globisporus N75, produced two glycosyltransferases, 6-alpha-glucosyltransferase (6GT) and 3-alpha-isomaltosyltransferase (IMT), jointly catalyzing formation of cyclo-->6)-alpha-D-Glcp-(1-->3)-alpha-D-Glcp-(1-->6)-alpha-D-Glcp-(1-->3)-alpha-D-Glcp-(1--> (CTS) from alpha-1,4-glucan. The N75 enzymes produced CTS from dextrin in a 43.8% yield at the reaction temperature of 50 degrees C, which was 10 degrees C higher than a critical temperature of CTS-forming by the enzymes from B. globisporus C11. The optimum temperatures for 6GT and IMT reactions were 55 degrees C and 50 degrees C, respectively. The thermal stability of both enzymes was 45 degrees C under the condition at pH 6.0 for 60 min. The genes for 6GT and IMT were cloned from the genomic DNA of N75. The amino acid sequences deduced from the 6GT and IMT genes showed 82% and 85% identities, respectively, to the sequences of the enzymes from C11. CTS yield was decreased by high concentrations of the substrate. It was found that the reaction yield was improved by adding cyclomaltodextrin glucanotransferase (CGTase). We demonstrated mass-production of CTS from starch by using the N75 enzymes and CGTase.