Utilization of Macroalgal Carbohydrates By The Marine Amoeba Trichosphaerium Sieboldi

Abstract

Trichosphaerium sieboldi is a marine amoeba with a cosmopolitan distribution. The ability of three strains, from different geographical regions, to digest a range of macroalgae was investigated. Prior to these experiments, methods were developed for the axenic cultivation of T. sieboldi. Algae included Fucus vesiculosus, F. spiralis, Laminaria digitata, L. saccharina, Mastocarpus stellatus, Palmaria palmata, Porhyra sp., and Ulva sp. All were degraded with equivalent ease; typically 50% of the tissue biomass was removed within seven days. The wall of this amoeba was studied to obtain clues on how a protist could be digesting macroalgal tissue. The fibrous nature of the outer cell wall presumably allows the wall to part and remesh during consumption of large particles. It is suggested that during digestion of macroalgae, the wall is parted to enable digestive enzymes to be localized along the surface of the seaweed wall, effectively forming an ‘enzyme pocket’. Trichosphaerium has both polysaccharidases and glycosidases, notably glucosidase, cellobiosidase, mannosidase and fucosidase. These enzymes work in concert to facilitate the breakdown of the complex polysaccharides found across the range of seaweeds used. These studies suggest that T. sieboldi could be a primary invader of seaweeds in the field. They also suggest that some protistan groups may be important in the degradation and recycling of algal material in coastal waters.