Levan-type fructooligosaccharides synthesis by a levansucrase-endolevanase fusion enzyme (LevB 1 SacB).

•SacB synthesizes a fructan polymer which may be simultaneously hydrolyzed by LevB1.•SacB and LevB1 behave efficiently as a new enzyme in the single protein LevB1SacB.•Levan FOS structures with DP from 2 to 10 are synthesized by the new fusion enzyme.•The levan-type FOS include levanbiose, blastose and 6-kestose as main products.