Production and characterization of an extracellular polysaccharide of antarctic marine bacteria Pseudoalteromonas sp. S-15-13

Twenty-seven antarctic bacteria producing extracellular polysaccharide (EPS) were selected from 57 strains by staining technology.The effects of major environmental factors on the growth and EPS production of Pseudoalteromonas sp.S-15-13 were investigated, and the EPS was separated and purified for characterization analysis.The results showed that the optimal conditions for the EPS production were culture period, 56 h; growth temperature, 8℃; carbon source, 1.0% glucose; NaCl concentration, 3.0%; pH 6.0~7.0.The EPS was purified by cold ethanol precipitation, proteins removal, ion exchange chromatography and gel chromatography technology.The molecular mass of EPS-Ⅱ was 62 kDa as determined by the high performance gel permeation chromatography.Its sugar composition was a homopolymer of mannose analyzed by gas chromatograph spectroscopy.After repeated freezing and thawing of the bacteria biomass in the presence of EPS, the bacterial growth was much higher than that observed after freezing in the absence of EPS and the difference augmented with the increase of freeze-thaw cycles.It is hypothesized that the adaptation of Pseudoalteromonas sp.S-15-13 to the antarctic marine conditions, characterized by low temperature, high NaCl concentration and repeated freeze-thaw cycles, might be related to the EPS production ability.