Factors affecting the production and molecular weight of levan in enzymatic synthesis by recombinant Bacillus subtilis levansucrase SacB-T305A

Levansucrase (EC 2.4.1.10) catalyzes both levan polymerization and sucrose hydrolysis. Levan production by recombinant Bacillus subtilis levansucrase SacB-T305A was investigated. The maximum conversion yield (33.09%) of sucrose to levan and levan yield (115.8 g L –1 ) were obtained as 30% (wt/vol) and 40% (wt/vol) initial sucrose, respectively. Under highly acidic conditions (pH 3.5 and below), the polymerization not only shifted distinctly to high molecular weight levan but also enlarged the size of low molecular weight levan. In particular, the proportion of high molecular weight levan to total products increased to 9-fold at pH 3.5. The presence of Fe 2+ , Mg 2+ , Mn 2+ and Zn 2+ ions at common ion strength (5 mmol L –1 ) increased only the size of low molecular weight levan from about 20 kDa to about 35 kDa. Our findings provide a supplementary view about the mechanism of levan molecular weight distribution in enzymatic synthesis and offer a possibility for producing levan of different molecular weights by modulating enzymatic reaction conditions. © 2020 Society of Industrial Chemistry