Levan-type fructooligosaccharides synthesis by a levansucrase-endolevanase fusion enzyme (LevB1SacB)

We describe here the enzymatic production of levan type-fructooligosaccharides (L-FOS) with a DP from 2 to 10, through simultaneous synthesis and hydrolysis reactions. This was accomplished by LevB1SacB, a new enzyme resulting from the fusion of SacB, a levansucrase from Bacillus subtilis and LevB1, an endolevanase from B. licheniformis. In the fusion enzyme, SacB retains its catalytic behavior with a decrease in kcat from 164 to 108 s−1. LevB1 in LevB1SacB kinetic behavior improves considerably reaching saturation with levan and following Michaelis-Menten kinetics, quite differently from the previously reported first order kinetic behavior. We also report that LevB1SacB or both enzymes (LevB1 & SacB) at equimolar concentrations in simultaneous reactions result in an optimal, wide and diverse L-FOS profile, including 6-kestose, levanbiose and blastose among other L-FOS and 1-kestose, which accumulates as by-product of SacB levan synthesis. Yields of around 40% (w/w) were obtained from 600 g/l sucrose with either LevB1SacB or LevB1 & SacB. The reaction was successfully scaled up to a stirred 2 l bioreactor.