Inhibition of CaCO₃ Precipitation by a Polysaccharide Associated with Coccoliths of Emiliania Huxleyi

Abstract

The coccolithophoridae are characterized by their ability to form a calcified cell cover consisting of calcite platelets called coccoliths. In Emiliania huxteyi the coccoliths are formed intracellularly under strict cellular control (De Jong et al., this volume). If the CaCO₃ of isolated coccoliths is dissolved in EDTA-NaOH pH 8.0, two macromolecular fractions can be obtained: an insoluble and a soluble fraction. When the insoluble fraction is submitted to acid hydrolysis (6 N HC1, 18 h, 100°C) monosaccharides and amino acids are released, indicating that the insoluble material contains polysaccharide and protein (1). Most of the insoluble fraction resists hydrolysis, however. The nature of this material remains to be investigated. The soluble fraction consists of a Ca²⁺-binding polysaccharide containing uronic acid and ester sulphate groups (2). Presumably part of the cellular control over calcification is mediated by this polysaccharide. Much of the work in our laboratory is focused on the question whether this polysaccharide plays a regulatory role in the nucleation, growth and/or termination of calcite crystallization.