Overexpression of secreted sucrose isomerase in Yarrowia lipolytica and its application in isomaltulose production after immobilization

Isomaltulose production by bacterial fermentation was limited, due to generation of undesirable products and reduced yields. Isomaltulose production using sucrose isomerase (SIase) catalyzed methods was expected to be more applicable, but was hampered by low SIase activity and lack of a secreted SIase producer. Here, we aimed to obtain high levels of secreted SIase by overexpressing the SIase gene from Pantoea dispersa UQ68J in Yarrowia lipolytica, a successful host for efficient secretory expression, with a newly characterized strong constitutive promoter. After optimization of the culture medium, the engineered strain JD secreted SIase with an activity of 49.3 U/mL. The recombinant SIase was effectively immobilized onto polyvinyl alcohol-alginate, and the enzymatic activity recovery rate was up to 82.4%. The stability of the SIase was significantly improved by immobilization. Batch production of isomaltulose catalyzed by the immobilized SIase was performed under optimal conditions, generating 620.7 g/L isomaltulose with a yield of 0.96 g/g. The conversion rate of sucrose after 13 batches remained above 90%. These results demonstrated that the proposed SIase expression and immobilization method was promising in the industrial production of isomaltulose.