The SEACELLS project was funded from October 2015 to October 2020 by a €2.7m European Research Council (ERC) Advanced Grant. SEACELLS addressed fundamental questions in phytoplankton biology from cellular to population scales. A particular focus was to better understand mechanisms that allow key phytoplankton types (coccolithophores and diatoms) to respond to changes in their environment. These phytoplankton form biomineralised structures (calcite coccoliths in coccolithophores and silica frustules in diatoms) that form protective coats on the cell surface.
Major outcomes of the project include:
- Discovery of a new class of eukaryotic ion channels (EUKCATS) in coccolithophores and diatoms. These ion channels are related structurally to a class of bacterial ion channels but play similar roles to more complex ion channels that are found in many other eukaryotes. We showed that EUKCATS play important roles in electrical excitability in coccolithophores and contribute to calcium-based intracellular signalling in diatoms.
- Parallel studies showed that diatoms possess sophisticated intracellular calcium signalling machinery enabling the cells to generate rapid calcium elevations in different cellular regions. We showed that these calcium elevations play key roles in the cells’ ability to perceive and respond to external stimuli, including changes in their osmotic environment, temperature and nutrient availability
- We also investigated the role of a different type of ion channel in the coccolithophore cell membrane that is permeable to hydrogen ions (protons). Calcification in coccolithophores involves the precipitation of calcium carbonate coccoliths in a specialised compartment within the cell. The chemistry of calcification means that a proton is produced for every molecule of calcium carbonate precipitated. These protons have the potential to acidify the cell to lethal levels (acidosis). We showed that proton channels have an important role in removing these calcification-produced protons from the cell, so regulating intracellular pH. However we also showed that the activity of these channels is severely compromised at lower seawater pH levels likely to be encountered in future ocean acidification scenarios. This work provides a mechanistic understanding of the response of a major phytoplankton group to ocean acidification.
- A further aspect of the SEACELLS project was to carry our cell physiological studies on natural phytoplankton populations. By participation in research cruises to the Southern Ocean, we were able to test new approaches for monitoring photosynthetic activity of single phytoplankton cells in different ecological contexts. This data along with parallel population genetic data is currently undergoing analysis.