A stray field magnetic resonance study of water diffusion in bacterial exopolysaccharides

Nuclear (H-1) magnetic stray field gradient methods have been used to measu re the concentration dependence of the water self-diffusion coefficient (D- self) in the commercially available bacterial exopolysaccharide xanthan and a chemically derived deacetylated form. The D-self coefficient of water is interpreted to directly relate to the degree of water binding in the polys accharide gel. The removal of acetyl groups from xanthan has been shown to result in a reduction in D-self at any given polymer concentration. In addi tion, stray field magnetic resonance profiling (H-1) has been used to measu re the rate at which water diffuses through a polysaccharide gel at a range of polymer concentrations (D-mutual coefficient of water) in: xanthan; dea cetylated xanthan and polymers produced by the soil bacteria, Enterobacter cloacae and Azotobacter chroococcum. Samples with a reduced acetyl or uroni c acid content showed a lower D-mutual coefficient at a range of polymer co ncentrations. The lower D-self coefficient found for deacetylated xanthan i s believed to contribute to the lower D-mutual coefficient obtained relativ e to the native molecule. The observed link between the mobility (D-self) a nd transport (D-mutual) of water in bacterial exopolysaccharides furthers o ur understanding of the role(s) of these materials for bacteria and opens n ew opportunities for engineering bacteria for improved survival in wafer-st ressed environments. (C) 1999 Elsevier Science Inc.