Characterisation of extracellular polysaccharides produced by Crypthecodinium cohnii

The valuable polyunsaturated fatty acid, docosahexaenoic acid, can be produ ced by cultivation of the heterotrophic microalga, Crypthecodinium cohnii. During batch growth of C. cohnii on glucose, sea salt and yeast extract for 5 days, so far unreported extracellular polysaccharides were produced. The se caused an increased viscosity and a strong drop in the maximum oxygen tr ansfer. The viscosity increased most markedly as cells entered the stationa ry phase. The polysaccharides varied in size (from 6 kDa to >1,660 kDa) and monomer distribution. A high molecular mass fraction (from 100 kDa to >1,6 60 kDa) and a medium molecular mass fraction (6-48 kDa) were prepared. The high molecular mass fraction contained (on a molar basis) 71.7% glucose, 13 .1% galactose and 3.8% mannose, whereas the medium molecular mass fraction contained 37.7% glucose, 19.8% galactose and 28.1% mannose. Other monomers present in both fractions were fucose, uronic acid and xylose. Monomers wer e coupled mainly via alpha-(1-3) links. Increased viscosity due to polysacc haride production complicates the development of commercial, high cell-dens ity processes for the production of docosahexaenoic acid.