High-level production of low-branched levan from Pseudomonas aurantiaca S-4380 for the production of di-beta-D-fructofuranose dianhydride IV

Abstract

The lscA gene, encoding a levansucrase of 424 amino acids (aa) residues, was cloned from the genomic DNA of Pseudomonas aurantiaca S-4380, and overexpressed in Escherichia coli. The recombinant levansucrase overexpressed in E. coli was then used to produce levan from sucrose. Levan crystals with 98% purity could be obtained from the reaction mixture with 62% yield using an alcohol precipitation method. The molecular weight of the levan was 7 x 10(5) daltons. Methylation studies showed that the levan was branched: main linkage C-2,6; branched linkage C-2,1; and degree of branching 6%. Three bacterial levans from different strains were incubated with levan fructotransferase (LFTase) from Arthrobacter ureafaciens K2032, which produced di-beta-D-fructofuranose dianhydride IV (DFA IV); final conversion yields from the levans to DFA IV were 39% in Zymomonas mobilis, 53% in Serratia levanicum, and 59% in P. aurantiaca S-4380 levansucrase. The levan from P. aurantiaca S-4380 levansucrase gave the highest conversion yield of levan to DFAIV so far reported.