Hydrodynamic characterisation of the exopolysaccharide from the halophilic cyanobacterium Aphanothece halophytica GR02: a comparison with xanthan

A bacterial exopolysaccharide from Aphanothece halophytica GR02 (AH-EPS) solubilised in buffered 1 M guanidine hydrochloride, GuHCl was studied using capillary viscometry, double gap viscometry, sedimentation velocity and sedimentation equilibrium using analytical ultracentrifugation. Results from capillary viscometry indicate that the exopolysaccharide is xanthan-like in its shear thinning properties. This was confirmed by double gap viscometry. Sedimentation velocity (distribution of apparent sedimentation coefficients) confirmed that the AH-EPS solution was reasonably homogeneous and a hyper-sharp boundary indicated that AH-EPS is a rigid/extra-rigid rod type polysaccharide. Sedimentation equilibrium confirmed the high molecular weight indicated by viscosity measurements. In order to ascertain whether the solution physical properties of AH-EPS are xanthan-like under the conditions studied, all the above experiments were repeated on a similarly treated xanthan solution in the same solvent. Results indicate that AH-EPS is indeed xanthan-like in its physical properties at least in the system studied. Xanthan properties in GuHCl do not appear too different from those studied in more traditional solvents.