Mapping calcium ion pools during calcification by the coccolithophore Gephyrocapsa huxleyi

Coccolithophores are unicellular marine algae capable of producing 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 the Earth’s atmosphere through the processes of photosynthesis and calcification. Calcite formation within coccolithophore cells is a fascinating process which is carried out within confined mineralisation vesicles and results in crystals displaying extraordinary morphologies with remarkable levels of hierarchical organisation. In order to produce coccoliths, a substantial quantity of calcium ions must be stored and transported, while keeping the cytosolic concentration of the ion low to avoid cytotoxicity and cell death. While calcium ion pools have been identified in coccolithophores, their precise roles in calcification still remain unclear.

The aim of this experiment is to is to use soft cryo-X-ray tomography of coccolithophore cells to characterize the mechanisms intracellular storage of calcium ions during calcification. This will be investigated by analyzing Gephyrocapsa huxleyi (formerly known as Emiliania huxleyi) cells at different stages of coccolith formation. The resulting 3D data will reveal 1) the location of the calcium ion pools with respect to the forming coccolith (e.g. if they are in close proximity); 2) the number, size and distribution of these ion pools; and 3) how their number, size and distribution change as calcification progresses. The recorded data will be used to build the understanding of biomineralisation processes and to predict the future behaviour of the marine carbon cycle in response to elevated atmospheric CO2 levels.