Structural analysis and characterization of dextran produced by wild and mutant strains of Leuconostoc mesenteroides

Abstract

An exopolysaccharide known as dextran was produced by Leuconostoc mesenteroides KIBGE-IB22 (wild) and L. mesenteroides KIBGE-IB22M20 (mutant). The structure was characterized using FTIR, (1)H NMR, (13)C NMR and 2D NMR spectroscopic techniques, whereas surface morphology was analyzed using SEM. A clear difference in the spectral chemical shift patterns was observed in both samples. All the spectral data indicated that the exopolysaccharide produced by KIBGE-IB22 is a mixture of two biopolymers. One was dextran in α-(1 → 6) configuration with a small proportion of α-(1 → 3) branching and the other was levan containing β-(2 → 6) fructan fructofuranosyl linkages. However, remarkably the mutant only produced dextran without any concomitant production of levan. Study suggested that the property of KIBGE-IB22M20, regarding improved production of high molecular weight dextran in a shorter period of fermentation time without any contamination of other exopolysaccharide, could be employed to make the downstream process more feasible and cost effective on large scale.

Keywords: (1)H NMR; (13)C NMR; 2D NMR; COSY; DQF-COSY; Dextran; EPS; Exopolysaccharide; FTIR; Fourier-transform infrared; HMBC; HSQC; KIBGE-IB22; KIBGE-IB22M20; Leuconostoc mesenteroides; Levan; Mutation; NOESY; ROESY; SEM; TOCSY; carbon nuclear magnetic resonance spectroscopy; double quantum-filtered phase-sensitive COSY; exopolysaccharide; heteronuclear multiple-bond correlation spectroscopy; heteronuclear single-quantum correlation spectroscopy; homonuclear correlation spectroscopy; mutant; nuclear Overhauser effect spectroscopy; proton nuclear magnetic resonance spectroscopy; rotating frame nuclear Overhauser effect spectroscopy; scanning electron microscopy; total correlation spectroscopy; two-dimensional nuclear magnetic resonance spectroscopy; wild type.