Extracellular polysaccharide production in Bacillus licheniformis SVD1 and its immunomodulatory effect

Abstract

Bacillus licheniformis SVD1 exhibited highest production of three different polysaccharides when sucrose was used as the carbon source for polysaccharide production and yeast extract was used as the nitrogen source. Polysaccharides were characterized using size exclusion chromatography (SEC), thin layer chromatography (TLC), gas chromatography with mass spectrometry (GCMS), and Fourier Transform Infrared (FTIR) analysis. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) were used to examine the topography of the cells and polysaccharides. The cell-associated polysaccharides were composed of galactose, while two different polysaccharides were present in the extracellular medium, one of 2,000 kDa (EPS1), consisting of fructose monomers and identified as a levan with (2→6)-linkages and (1→2)-branching linkages. The other extracellular polysaccharide (EPS2) consisted of mannose and galactose and had a range of sizes as identified through SEC. All three polysaccharides displayed an immune modulatory effect as measured using Interleukin 6 (IL6) and tumor necrosis factor alpha (TNFα).