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Efficient production of levan using a recombinant yeast Saccharomyces cerevisiae hypersecreting a bacterial levansucrase

Ko, Hyunjun, Bae, Jung-Hoon, Sung, Bong Hyun, Kim, Mi-Jin, Kim, Chul-Ho, Oh, Baek-Rock, Sohn, Jung-Hoon
Journal of industrial microbiology & biotechnology 2019 v.46 no.11 pp. 1611-1620
Rahnella aquatilis, Saccharomyces cerevisiae, amino acids, batch fermentation, cost effectiveness, culture media, fermenters, fructose, industry, levan, levansucrase, membrane proteins, mitochondria, polymers, protein secretion, sucrose, yeasts
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.