Study On Different Cultivation Methods Of Nostoc Flagelliforme And Separation Of Its Polysaccharides

With different photobioreactors, Nostoc flagelliforme cells was liquid cultured in open, closed and cyclic culture ways. The effects of different culture conditions on N.flagelliforme growth and yield of extracellular polysaccharide (EPS) were studied. The isolation and purification of polysaccharide from mixotrophic, autotrophic and heterotrophic cultivation of N.flagelliforme cells were conducted. The results are as follows:(1) Simple air-lift photobioreactors were made using5L filtration bottles for open and close-end cultivation of N.flagelliforme cells in this study. The growth rate and polysaccharide production all increased with the increase of light intensity in10to60μmol·m-2·s-1of illumination intensity. Continuous light is more suitable to N.flagelliforme cell growth and polysaccharide accumulation. When the close-end culture was carried out in0.7vvm of ventilation,60μmol·m-2·s-1of light intensity and continuing light conditions, the biomass and the polysaccharide production reached1.7g/L and89.32mg/L respectively.(2) The results of25L open pond cultivation proved that stepwise increased light intensity and fed-batch culture is more helpful to N.flagelliforme cell growth and polysaccharide accumulation.(3) The20L photobioreactor was used for cyclic liquid cultivation of N.flagelliforme cells. The result showed that the highest biomass and chlorophyll a are1.608g·L-1and9.744μg·mL-1respectively and they all decreased with the increase of cultivation times. However, for EPS production, the second time was the highest. It raised by24.3%than the first time cultivation. Nostoc flagelliforme cells appear etiolated in the third culture because of serious lack of nutrients. When nutrients were replenished to the medium, the biomass, the growth rate and EPS came up to1.478g·L-1,0.048d-1and135.57mg·L-1respectively, which showed replenishing nutrients to the medium can make the biomass and EPS maintain at a high level.(4) The purification and comparison of the three different polysaccharides from mixotrophic, autotrophic and heterotrophic cultivation of N.flagelliforme cells were done by means of ion exchange chromatography and gel chromatography. The ion exchange chromatography showed one fraction for both the polysaccharides from mixotrophic and autotrophic cultivation, however, polysaccharide from heterotrophic culture showed two fractions. The eluting profile of gel chromatography revealed one fraction for each of the different EPS and the peaks were basically in the same range, which showed the molecular masses of all different EPS are very close.