An inventory of factors that affect polysaccharide production by Phaeocystis globosa

Phaeocystis material contains polysaccharides that are built from at least eight different monosaccharides. Differences have been reported between the carbohydrate composition of different Phaeocystis species, and also betwee n samples taken from Phaeocystis globosa blooms in different areas. In orde r to elucidate factors that could play a role in determining Variation in c arbohydrate composition and production, a number of Phaeocystis globosa str ains were studied under laboratory conditions. Although there was a clear d istinction of a northern and a southern cluster in the Phaeocystis globosa strains based on RAPD analysis, the differences in the composition of the m ucopolysaccharides were relatively small. The contribution of glucose, howe ver, ranged from 7-85% of total sugars. A strain that was cultured in seawa ters of diverse origin produced polysaccharides of a different composition, suggesting the effect of environmental factors. The presence of bacteria a ffected neither the amount, nor the composition of the carbohydrates that w ere produced by Phaeocystis globosa. Glucose is part of both the intracellu lar polysaccharide pool and of the mucopolysaccharides in the colony matrix . Using specific digestion of the intracellular chrysolaminaran by laminari nase, the distribution of polysaccharides over different pools could be ass essed. During growth of an axenic, mucus-producing strain, the portion of g lucose present as chrysolaminaran appeared to increase. The polyglucose tha t was not digested by laminarinase remains unidentified. This study shows t hat environmental factors rather than strain differences determine differen ces in the sugar composition of Phaeocystis globosa, especially with respec t to the glucose content of the material. A difference in the contribution of glucose could be correlated to the portion of cells in the culture that are not in the colonies. Our study emphasises that for studying polysacchar ide dynamics in Phaeocystis globosa it is important to be able to discrimin ate between the different polysaccharide pools. Preliminary results of an e nzymatic approach were promising (C) 2000 Elsevier Science B.V. All rights reserved.