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

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 β-galactosidase gene from Aspergillus oryzae to the YlPir1 gene, which codes for a cell wall protein. β-Galactosidase was effectively displayed on the cell surface of Yarrowia lipolytica start strain CGMCC7326. This engineered strain with surface-displayed β-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 °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 °C, about 20 °C higher than that of free β-galactosidase, which was helpful for enhancing the reaction rate and GOS production.