Efficient constitutive expression of thermostable 4-alpha-glucanotransferase in Bacillus subtilis using dual promoters

Abstract

4-alpha-Glucanotransferases possess strong transglycosylation activity which has been used in various carbohydrate chemistry fields. Due to safety issues of the recombinant enzymes we chose Bacillus subtilis as an expression host to produce a thermostable 4-alpha-glucanotransferase from Thermus scotoductus (TS alpha GT). The HpaII promoter in the Gram-positive bacterial vector pUB110 was used first to express TS alpha GT gene in B. subtilis. However, the activity of TS alpha GT in B. subtilis was only 4% of that in our previous Escherichia coli system. Two expression systems constructed by sequential alignment of another constitutive promoter for either alpha-amylase from B. subtilis NA64 or maltogenic amylase from Bacillus licheniformis downstream of the HpaII promoter elevated the TS alpha GT productivity by 11- and 12-fold, respectively, compared to the single HpaII promoter system. In conclusion, the dual promoter systems in this study were much better than the single promoter system to express the TS alpha GT gene in B. subtilis.