An Alternative Approach to Synthesizing Galactooligosaccharides by Cell-Surface Display of beta-Galactosidase on Yarrowia lipolytica

摘要

An alternative strategy for synthesizing galactooligosaccharides (GOS) from an erythritol-producing yeast Yarrowia lipolytica using surface display technology was demonstrated. The engineered strain CGMCC11369 was developed by fusion of the beta-galactosidase gene from Aspergillus oryzae to the YlPir1 gene, which codes for a cell wall protein. beta-Galactosidase was effectively displayed on the cell surface of Yarrowia lipolytica start strain CGMCC7326. This engineered strain with surface displayed beta-galactosidase efficiently synthesized GOS from lactose. An amount of 160 g/L GOS was produced within 6 h in a solution of 500 g/L lactose and 5 mg/mL cell (dry weight) at pH 5.5 and 60 degrees C, with a yield of 51% of consumed lactose monohydrate. This newly developed method was applied with waste yeast paste from erythritol industry at least 10 times. The optimal reaction temperature increased to 60 degrees C, about 20 degrees C higher than that of free beta-galactosidase, which was helpful for enhancing the reaction rate and GOS production.