Biosynthesis and Structural Characterization of Levan by a Recombinant Levansucrase From Bacillus Subtilis ZW019

Abstract

ObjectivesThe yield of levan extracted from microbial fermentation broth is low, so in vitro catalytic synthesis of levan by levansucrase is expected to be one of the industrial production approaches of levan. ResultsA recombinant plasmid Pet-28A-AcmA-Z constructed in the previous study was used to produce levansucrase. The recombinant levansucrase could be easily purified in one step and the purified enzyme had a single band clearly visible in SDS-PAGE. The conditions for enzymatic reactions was optimal at pH 5.2 and 40 ℃, and the activity of enzymes was stimulated by K+ and Ca2+. The yield of levan biosynthesis from 10% (w/v) sucrose with 6.45 U/g sucrose of levansucrase was 30.6 g/L. The molecular weight of the levan was about 1.56×106 Da, as measured by GPC. HPIC analysis showed that the monosaccharide composition of the levan was fructose and glucose. The results of FTIR and NMR analysis indicated that the polymer produced by the recombinant levansucrase was β-(2, 6) levan.ConclusionsThe results of this study provide a basis for large-scale production of levan by enzymatic method.