An Approach for Lactulose Production Using the CotX-Mediated Spore-Displayed β-Galactosidase as a Biocatalyst
2016
Wang, H., Jiangnan University, Wuxi, China | Yang, R., Jiangnan University, Wuxi, China | Hua, X., Jiangnan University, Wuxi, China | Zhang, W., Jiangnan University, Wuxi, China | Zhao, W., Jiangnan University, Wuxi, China
Currently, enzymatic synthesis of lactulose, a synthetic prebiotic disaccharide, is commonly performed with glycosyl hydrolases. In this work, a new type of lactulose-producing biocatalyst was developed by displaying beta-galactosidase from Bacillus stearothermophilus IAM11001 (Bs-beta-Gal) on the surface of Bacillus subtilis 168 spores. Localization of beta-Gal on the spore surface as a fusion to CotX was verified by western blot analysis, immunofluorescence microscopy, and flow cytometry. The optimum pH and temperature for the resulting sporedisplayed beta-Gal was 6.0 and 75Celsius, respectively. Under optimal conditions, it showed maximum activity of 0.42 U/mg spores (dry weight). Moreover, the spore-displayed CotX-beta- Gal was employed as a whole cell biocatalyst to produce lactulose, yielding 8.8 g/l from 200 g/l lactose and 100 g/l fructose. Reusability tests showed that the spore-displayed CotX-beta- Gal retained around 30.3% of its initial activity after eight successive conversion cycles. These results suggest that the CotX-mediated spore-displayed beta-Gal may provide a promising strategy for lactulose production.
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