Structure-activity relationship of the exopolysaccharide from a psychrophilic bacterium : a strategy for cryoprotection

Microrganisms from sea ice, glacial and subglacial environments are currently under investigation due to their relevant ecological functions in these habitats, and to their potential biotechnological applications. The cold-adapted Colwellia psychrerythraea 34H produces extracellular polysaccharides with cryoprotection activity. We here describe the purification and detailed molecular primary and secondary structure of the exopolysaccharide (EPS) secreted by C. psychrerythraea 34H cells grown at 4°C. The structure was determined by chemical analysis and NMR. The trisaccharide repeating unit of the EPS is constituted by a N-acetyl quinovosamine unit and two residues of galacturonic acid both decorated with alanine. In addition, the EPS was tested in vitro showing a significant inhibitory effect on ice recrystallization. In-depth NMR and computational analysis suggest a pseudohelicoidal structure which seems to prevent the local tetrahedral order of the water molecules in the first hydration shell, and could be responsible of the inhibition of ice recrystallization. As cell cryopreservation is an essential tool in modern biotechnology and medicine, the observations reported in this paper could pave the way for a biotechnological application of Colwellia EPS