Structural and Functional Diversity of Acidic Polysaccharides from Various Species of Coocolithophorid Algae)

Coccolith is a calcified scale with species-specific fine structure produced by marine unicellular coccolithophorid algae and consists of CaCO3 crystals (calcite) and organic matrices. All calcifying strains of coccolithophorid algae, Emiliania huxleyi, Gephyrocapsa oceanica and Pleurochrysis carterae, contained acidic polysaccharides (APSs). These APSs are considered to play a regulatory function in CaCO3 crystallization. EDTA-soluble APSs from whole cells inihibited CaCO3 crystallization in a dose-dependent manner in vitro. The APSs completely inhibited at the concentrations of 1-10 µg/ml. The most active APS was obtained from P. carterae and induced vaterite formation in a CaCO3 supersaturated solution at 24 hr after the addition of APS. Structural diversity of APSs from coccoliths was found within the Pleurochrysis genus; P. carterae CCMP 645 contained APS, designated as PS-2, reported previously, while P. haptonemofera contained another APS, designated as CMAP, which was structurally related to PS-2. In contrast, P. carterae CCMP 646 and CCMP 648 contained both PS-2 and CMAP. CMAP completely inhibited CaCO3 crystallization at the concentration of 1µg/ml, while PS-2 did not show any inhibitory activity even at the concentration of 100 µg/ml.