Properties of a Highly Viscous Polysaccharide Produced by a<i>Bacillus</i>Strain Isolated from Soil

Abstract

Chemical and Theological properties of a highly viscous and acidic polysaccharide produced by a soil bacterium identified as Bacillus circulans are described. The molecular weight of the native polysaccharide was about 116 × 10(4) by gel filtration with HPLC. The molar ratio of D-galactose, n-mannose, and L-rhamnose contained in the polysaccharide as neutral sugar components was 1.3:1:2. The viscosity of 1% solution of the polysaccharide was about 5000 cp, which was higher than that of guar gum, a seed polysaccharide, used as a reference standard. The viscosity was affected by the pH of the polysaccharide solution, a maximum viscosity being observed at pH 5.5 for native and decationized polysaccharide solution. The viscosity of 0.3% solution was decreased to about 70% by heating at 100°C and 22% at 120°C for 30 min as compared to the viscosity before heating. The addition of sugars, especially sucrose and glucose, at 10-30% concentration brought about a 130-180% increase of the viscosity. The addition of CaCl2 at a low concentration markedly increased the viscosity, and a maximum viscosity was attained at 2% concentration of the salt.