Marine plankton uses animal-like gateway to maintain chemical
balance.
23rd June 2011
The production of calcium carbonate structures, such as
coral reefs and shells, by marine organisms plays a key role in the
Earth’s carbon cycle and can ultimately lead to the formation of
sedimentary deposits that, through time, become chalk and
limestone.
Major contributors to this marine calcification are the
coccolithophores, a family of single-celled algae that surround
themselves with calcified plates known as coccoliths. This
beautiful, plated armour is different to that of other calcifiers
in that it is produced inside the cell through a precisely
controlled process. But there is a down side, a by-product of the
lith formation is the production of hydrogen ions, which can raise
the acidity of the cell and lead to damage, if not regulated.
In order to avoid such damage the cell has to remove the
hydrogen ions before the cell is acidified. Understanding how the
coccolithophore achieves this life-saving activity could lead to a
greater understanding of how the alga and other organisms might
cope in the face declining pH values resulting from ocean
acidification, a result of increased quantities of anthropogenic
CO2 being emitted to the atmosphere and ultimately being
absorbed at the sea surface.
PML scientist Glen Wheeler, working with colleagues from
the Marine Biological Association and the University of North
Carolina, has discovered that coccolithophores have special
channels which allows the hydrogen ions to be removed. The channel
is opened via a ‘voltage-gate’ which draws the hydrogen ions out of
the cell, maintaining pH at a safe level and ensuring the health of
the organism. These channels are extremely sensitive to changes in
seawater pH and are therefore likely to play an important role in
the response of coccolithophores to ocean acidification. Until now
this voltage-gated mechanism had only been seen in multi-cellular
animals, such as vertebrates, the occurrence in algae raises the
tantalising possibility of an early common ancestor.