Cryoprotective exopolysaccharide produced by the antarctic bacterium Pseudoalteromonas arctica KOPRI 21653

Abstract

Among the seven bacterial strains isolated for the ability to secrete cryoprotective exopolysaccharides from King George Island, Antarctica, Pseudoalteromonas arctica KOPRI 21653 was selected for further study of an anti-ice-nucleating polysaccharide from a polar region. The exopolysaccharide (P-21653) was purified from KOPRI 21653 culture via column chromatography and protease treatment. The major sugar components of P-21653 were determined to be galactose and glucose at a ratio of 1:1.5 by GC-MS analysis. The cryoprotective activity of P-21653 was characterized using an E. coli viability test. In the presence of 0.1% P-21653, the survival ratio of E. coli cells was as high as 82.6% in three repeated freeze-thaw cycles. The survival ratio drastically decreased to 71.5 and 48.1%, respectively, in five and seven repeated cycle conditions

however, the survival ratios were greater during three (96.6-92.1%) to seven (100.5-91.6%) cycles in the presence of 0.5 and 1.0% P-21653. In addition, at much lower concentrations (0.1-1.0%), P-21653 resulted in survival ratios (83.1-98.4%) similar to those of two commercially available cryoprotectants (VEG plus X-1000, 92.9% and VM3, 95.3%), which were used at the recommended concentration of 90%. The biochemical characteristics suggests that P-21653 may be developed as a useful cryoprotectant in medical applications.