Biomineralisation in Coccolithophores

In Nature, organisms from all 5 kingdoms are well known to produce a wide range of organic-inorganic hybrid materials that fulfill a large number functions. Examples are shells and coral skeletons that give protection for the animals, and vertebrate bone that provide mechanical support and protection for the body. Coccolithophores are among the most striking examples of biomineralisation in nature. These organisms are unicellular marine algae that produce coccoliths – hierarchical, disk-shaped micro assemblies of calcite crystals – that play an important role in the global carbon cycle, allowing the excess greenhouse CO₂ to be removed from Earth atmosphere through the process of photosynthesis and calcification. Calcite formation within these organisms is a fascinating process which is carried out within confined mineralisation vesicles and results in crystals displaying extraordinary morphologies linked with remarkable levels of hierarchical organisation. Here, we will discuss the roles of the biochemical components within the mineralization vesicles – coccolith-associated polysaccharides and the organic scaffold onto which the crystals nucleate and grow – in controlling crystal, nucleation, growth and polymorph type.