Discovery and Enzymatic Screening of Genome-Mined Microbial Levanases to Produce Second-Generation β-(2,6)-Fructooligosaccharides: Catalytic Properties

Abstract

Evidence suggests that β-(2,6)-levan-type fructooligosaccharides (FOSs) possess higher prebiotic potential and selectivity than their β-(2,1)-inulin-type counterparts. The focus of the present work was to develop an enzymatic approach for the synthesis of levan-type FOSs, employing levanases (EC 3.2.1.65), specifically those performing endo-hydrolysis on levans. To identify new levanases, a selection of candidates was obtained via in silico exploration of the levanase family biodiversity through a sequence-driven approach. A collection of 113 candidates was screened according to their specific activities on low- and high-molecular-weight (MW) levan as well as thermal stability. The most active levanases were able to hydrolyze both types of levan with similar efficiency. This ultimately revealed 10 active, highly evolutionary distant and diverse candidate levanases, which demonstrated preferential hydrolysis of levan over inulin. The end-product profile differed significantly depending on levanase with levanbiose, levantriose, and levantetraose being the major FOSs. Among them, the catalytic properties of 5 selected potential new levanases (LEV9 from Belliella Baltica, LEV36 from Dyadobacter fermentans, LEV37 from Capnocytophaga ochracea, LEV79 from Vibrio natriegens, LEV91 from Paenarthrobacter aurescens) were characterized, especially in terms of pH and temperature profiles, thermal stability, and kinetic parameters. The identification of these novel levanases is expected to contribute to the production of levan-type FOSs with properties surpassing those of commercial preparations.