Microbial breakdown of Phaeocystis mucopolysaccharides

Mucus from the microalga Phaeocystis was partially purified and used as the C source in various stable enrichment cultures wherein the mucus carbohydr ates were degraded under oxic as well as anoxic conditions. The breakdown o f mucopolysaccharides (initially at a rate of 50% in 11 d at 12 degrees C) markedly slowed after about 15 d, leaving a fraction nondegraded. The carbo hydrate composition of the residual fraction did not change during breakdow n. It was shown that the incomplete degradation of mucopolysaccharides was not due to inherent resistance to breakdown in parts of the mucus carbohydr ates but to the release of inhibitors produced during breakdown. The (poten tially high) overall degradability of mucopolysaccharides has important con sequences for the fate of C fixed by Phaeocystis. The balance between recyc ling of Phaeocystis biomass in surface waters and its accumulation, sedimen tation, and burial in the sediment will greatly depend on factors such as n utrient availability, presence of inhibiting agents, and composition of the microbial community, rather than on structural impediments inhibiting muco polysaccharide degradation.