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

A bacterial exopolysaccharide from Aphanothece halophytica GR02 (AH-EPS) so lubilised in buffered 1 M guanidine hydrochloride, GuHCl was studied using capillary viscometry, double gap viscometry, sedimentation velocity and sed imentation equilibrium using analytical ultracentrifugation. Results from c apillary 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 coefficient s) confirmed that the AH-EPS solution was reasonably homogeneous and a hype r-sharp boundary indicated that AH-EPS is a rigid/extra-rigid rod type poly saccharide. Sedimentation equilibrium confirmed the high molecular weight i ndicated by viscosity measurements. in order to ascertain whether the solut ion physical properties of AH-EPS are xanthan-like under the conditions stu died, all the above experiments were repeated on a similarly treated xantha n solution in the same solvent. Results indicate that AH-EPS is indeed xant han-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. (C) 2001 Elsevier Science Ltd. All rights reserved.