The world's oceans support vast populations of single-celled organisms (phytoplankton) that are responsible, through photosynthesis, for removing about half of the carbon dioxide that is produced by burning fossil fuels as much as the rainforests and all other terrestrial systems combined. One group of phytoplankton, known as the coccolithophores, are known for their remarkable ability to build chalk (calcium carbonate) scales inside their cells, which are secreted to form a protective armour on the cell surface. On a global scale this calcification process accounts for a very significant flux of carbon from the surface ocean, and hence coccolithophores are an important component of the global carbon cycle, as cells die and the calcium carbonate sinks to form ocean sediments.
In an article published in PLoS Biology on 21st June, a team of scientists from the Marine Biological Association and Plymouth Marine Laboratory in the UK and the University of North Carolina Wilmington, USA report the unexpected finding that coccolithophores use a similar mechanism to the one previously characterised in vertebrate cells, to facilitate calcification. They found that this process may be directly affected by the current increasing levels of dissolved carbon dioxide in the oceans.
The armour scales of coccolithophores are formed by transporting calcium and bicarbonate into the cell where they combine to form calcium carbonate. Calcification is a strongly pH-dependent process and is likely to be affected by the increase in carbon dioxide levels that are making the ocean increasingly acidic.
The researchers used a combination of single cell physiology and molecular biology to identify the molecular machinery that underlies calcification. A by-product of the calcification reaction is the formation of protons (H+) inside the cell. "These H+ ions can potentially accumulate in the cell causing it to become acidic - a process know
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