Abstract
Levan has wide applications in chemical, cosmetic, pharmaceutical and food industries. The free levansucrase is usually used in the biosynthesis of levan, but the poor reusability and low stability of free levansucrase have limited its large-scale use. To address this problem, the surface-displayed levansucrase in Saccharomyces cerevisiae were generated and evaluated in this study. The levansucrase from Zymomonas mobilis was displayed on the cell surface of Saccharomyces cerevisiae EBY100 using a various yeast surface display platform. The N-terminal fusion partner is based on a-agglutinin, and the C-terminal one is Flo1p. The yield of levan produced by these two whole-cell biocatalysts reaches 26 g/L and 34 g/L in 24 h, respectively. Meanwhile, the stability of the surface-displayed levansucrases is significantly enhanced. After six reuses, these two biocatalysts retained over 50% and 60% of their initial activities, respectively. Furthermore, the molecular weight and polydispersity test of the products suggested that the whole-cell biocatalyst of levansucrase displayed by Flo1p has more potentials in the production of levan with low molecular weight which is critical in certain applications. In conclusion, our method not only enable the possibility to reuse the enzyme, but also improves the stability of the enzyme.
Highlights
Levan is a polysaccharide with diverse probiotic functions that is currently receiving increasing attention
The efficiency of levansucrase utilization has been improved mainly by immobilization [5,6,7], e.g., Zymomonas mobilis levansucrae was immobilized in the chitin-binding domain to obtain 83 g/L levan [8], the cost of enzyme preparation via immobilization is still an major obstacle to the application of enzymatic synthesis of levan
The results demonstrate the two recombinant strains can be repeatedly used as whole-cell catalyst to produce levan from sucrose
Summary
Levan is a polysaccharide with diverse probiotic functions that is currently receiving increasing attention. Levan consists of fructose units mainly linked by β (2,6) glycosidic bonds, with β (2,1) linked side chains [2]. It can be obtained by chemical synthesis, microbial fermentation or enzymatic synthesis. The enzymatic synthesis of levan has more industrial prospects It is based on the direct polymerization of the fructose group of sucrose by transglycosylation using levansucrase (EC 2.4.1.10) [4]. The preparation efficiency, stability and reusability of levansucrase limits the application of levan enzymatic synthesis methods. The efficiency of levansucrase utilization has been improved mainly by immobilization [5,6,7], e.g., Zymomonas mobilis levansucrae was immobilized in the chitin-binding domain to obtain 83 g/L levan [8], the cost of enzyme preparation via immobilization is still an major obstacle to the application of enzymatic synthesis of levan
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