Isolation, structural characterization and immunological activity of an exopolysaccharide produced by Bacillus licheniformis 8-37-0-1

A strain of Bacillus licheniformis 8-37-0-1 with high exopolysaccharide (EPS) production ability was isolated and identified based on morphological and physiological characteristics and phylogenetic analysis of 16S rDNA sequences. A new type of EPS was isolated from the strain fermentation broth by enzymolysis, isopropanol precipitation, anion-exchange, and gel-filtration chromatography. The new EPS was determined as homogeneous, with a molecular weight of 2.826 × 104, as determined by High-Performance Size-Exclusion Chromatography Multi-Angle Laser Light Scattering analysis. Its structural characteristics were investigated and elucidated by methylation analysis, partial acid hydrolysis, gas–liquid chromatography mass spectrometry, Fourier transform infrared, and nuclear magnetic resonance spectroscopy. Based on obtained data, the EPS was found to be a levan containing a (2 → 6)-linked backbone with a single β-d-fructose at the C-1 position every seven residue, on average, along the main chain. Preliminary in vitro tests revealed that EPS could significantly stimulate the proliferation of spleen lymphocyte.