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

Nuclear ( 1H) magnetic stray field gradient methods have been used to measure 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 polysaccharide 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 addition, stray field magnetic resonance profiling ( 1H) has been used to measure the rate at which water diffuses through a polysaccharide gel at a range of polymer concentrations ( D mutual coefficient of water) in: xanthan; deacetylated xanthan and polymers produced by the soil bacteria, Enterobacter cloacae and Azotobacter chroococcum. Samples with a reduced acetyl or uronic acid content showed a lower D mutual coefficient at a range of polymer concentrations. The lower D self coefficient found for deacetylated xanthan is believed to contribute to the lower D mutual coefficient obtained relative to the native molecule. The observed link between the mobility ( D self ) and transport ( D mutual ) of water in bacterial exopolysaccharides furthers our understanding of the role(s) of these materials for bacteria and opens new opportunities for engineering bacteria for improved survival in water-stressed environments.