Chain conformation and rheological behavior of exopolysaccharide from Bacillus mucilaginosus SM-01

The chain conformation and rheological behavior of an acidic hetero-exopolysaccharide from Bacillus mucilaginosus (BMPS) in aqueous solution were evaluated by using static and dynamic light scattering, viscometry and atomic force microscopy (AFM). BMPS displayed typical polyelectrolyte behavior in pure water and the intrinsic viscosity dramatically decreased with the addition of NaNO3. The Huggins constants k' of 0.303 and the positive second virial coefficient A(2) of BMPS in 0.1 M NaNO3 aqueous solution at 25 degrees C suggested that 0.1 M NaNO3 aqueous solution was a good solvent for BMPS. The relative stiffness parameter (B-value) was estimated to be 0.018, indicating the semi-flexibility of the BMPS backbone. The dependences among the intrinsic viscosity ([eta]) and the radius of gyration ((1/2)) on molecular weight (M-w) in the range of M-w from 265 x 10(4) to 37.3 x 10(4) g mol(-1), as well as the ratio of geometric to hydrodynamic radius revealed that BMPS exhibited an extended coil geometry in 0.1 M NaNO3 aqueous solution. The molecular size and shape of BMPS was further characterized by a wormlike cylinder model and observed directly by using AFM. The rheological results indicated that BMPS in pure water exhibited strong shear thinning property, and viscoelastic behavior was observed with solutions within 1.4-2.7% (w/v) consistent with the formation of entangled macromolecules in solution. (C) 2016 Elsevier Ltd. All rights reserved.