Production of exopolysaccharides by selected Bacillus strains: Optimization of media composition to maximize the yield and structural characterization

Selected Bacillus strains were investigated for the production of exopolysaccharides (EPS) by fermentation in three different culture media: (i) mineral base-medium with added yeast extract (M1), (ii) succinate-containing mineral base-medium with added yeast extract (M2) and (iii) tryptone and yeast extract-containing base-medium (M3). Modest EPS yield of 6.7 g/L was recorded for Bacillus amyloliquefaciens 23350 grown on M1, where the EPS produced was characterized by a low MW (<5 kDa) and of being mainly glucans. The most significant yield (48.57 g/L) was obtained with Bacillus licheniformis 14580 in M2; the EPS produced was 5-30 kDa in size and characterized by an exceptionally heterogeneous monosaccharide profile with galactose, fructose and glucose as the predominating monomers. The use of M1 medium for the growth of B. licheniformis 14580 resulted in low yield; however, the obtained heteropolymers EPS were characterized by a higher MW 30-100 kDa. The effect of the concentrations of yeast extract, sodium succinate and sucrose on the EPS production by B. licheniformis 14580 were studied using response surface methodology analysis. Greater EPS yields were achieved with increased concentrations of sodium succinate and sucrose and with decreased concentrations of yeast extract in the mineral media.