Efficient production of levan using a recombinant yeast Saccharomyces cerevisiae hypersecreting a bacterial levansucrase
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Levan is a fructose polymer with diverse applications in the food and medical industries. In this study, levansucrase from Rahnella aquatilis (RaLsrA) was hyper-secreted using a Saccharomyces cerevisiae protein secretion system. An optimal secretion signal, a translation fusion partner (TFP) containing an N-terminal 98 amino acid domain from a mitochondrial inner membrane protein, UTH1, was employed to secrete approximately 50 U/mL of bioactive RaLsrA into culture media with 63% secretion efficiency by fed-batch fermentation. Although the purified RaLsrA was useful for enzymatic conversion of high-molecular-weight levan of approximately 3.75 × 106 Da, recombinant yeast secreting RaLsrA could produce levan more efficiently by microbial fermentation. In a 50-L scale fermenter, 76-g/L levan was directly converted from 191-g/L sucrose by recombinant yeast cells, attaining an 80% conversion yield and 3.17-g/L/h productivity. Thus, we developed a cost-effective and industrially applicable production system for food-grade levan.
KeywordsLevan Saccharomyces cerevisiae Levansucrase Recombinant protein expression Direct fermentation
This work was supported by the Advanced Biomass R&D Center, Global Frontier Program of Korea Ministry of Science and ICT (2010-0029737), the Technology development Program (S2667724) funded by the Korea Ministry of SMEs and Startups and the Research Initiative Program of KRIBB.
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