High-level expression of sucrose isomerase in Bacillus subtilis through expression element optimization and fermentation optimization

Abstract

Abstract Sucrose isomerase is an important food enzyme that catalyze the isomerization of sucrose into isomaltulose, a functional sugar widely used in food industrial, while the production level of sucrose isomerase in food safe host strains was much low than industrial requirement. Bacillus subtilis is an excellent host strain for recombinant protein expression, which own the characteristics of powerful secretory capability and generally recognized as safe state. In this study, the expression of sucrose isomerase in B. subtilis was improved through expression element optimization and fermentation optimization. Firstly, the extracellular chaperone PrsA was overexpressed to enhance extracellular folding of sucrose isomerase, which improved the recombinant expression level by 80.02%. Then, the protein synthesize level was optimized through promoter screening, improving the recombinant expression level by 60.40%. On the basis of strain modification, the fermentation conditions including nitrogen source, carbon source, metal ion, pH and temperature were optimized successively in shake-flask. Finally, the 3 L bioreactor cultivation condition was optimized and yielding a sucrose isomerase activity of 862.86 U/mL, the highest level reported to date. This study provides an effective strategy to improve the expression level of food enzymes in B. subtilis.