Preprint volume - SIBM

Pre-print Volume – Introductory lectures
Topic 2: MARINE ORGANISMS AND ECOSYSTEMS AS MODEL SYSTEMS
machinery in bringing about the required fluxes? What are likely to be the effects of
decreased ocean pH on the calcification process? Changes in ocean pH will potentially
affect both the speciation of carbon in the ocean, the dissolution of calcite and the
ability of cells to remove protons. Only by acquiring more detailed knowledge of
transport processes and their regulation will we be able to address these fundamental
questions.
Results - We have adopted a combination of cell physiological, genomic and
molecular approaches to try to understand the mechanisms underlying calcification.
Our electrophysiological studies have shown some unique features of the coccolith
membrane physiology and the presence of unexpected ion channels (Taylor and
Brownlee, 2003). For example, coccolithophores have similar ion channels to those
involved in generating action potentials in animals and indeed we have shown the
occurrence of spontaneous action potentials in single coccolithophore cells (Taylor and
Brownlee, 2003). More recently we have shown the presence of an ion conductance
pathway in the plasma membrane that allows protons to efflux from the cell down their
electrochemical potential gradient. Recent combination of genomic, imaging and patch
clamp electrophysiology has shown for the first time in a non-animal cell the presence
of the molecular counterpart of the proton channel that is able to perform this function.
We have proposed that this is involved in short-term pH regulation and its activity is
essential for calcification.
We have also begun to characterize other transporters that genomics studies indicate
are involved in calcification since their expression levels are strongly dependent on
calcification. These include a putative calcium/proton exchanger and an anion
exchanger that may be involved in inorganic carbon transport.
Genomics studies are also beginning to allow an understanding of the genetic
variability in populations of coccolithophores that will be important in understanding
how these organisms may respond or adapt to changing seawater chemistry. One
particular gene (GPA) that encodes a protein that is intimately associated with the
coccolith crystals has been shown to vary in sequences that correlate with coccolith
morphology. We are beginning to map the occurrence of different coccolith
morphotypes at the molecular level to gain an understanding of the genetic variability
in existing coccolith populations. Collaborations with the Sir Alistair Hardy
Foundation for Ocean Science Continuous Plankton Recorder (CPR) are for the first
time enabling the molecular composition of past coccolithophore populations to be
reconstructed.
Conclusions – Understanding the mechanisms of calcification at the molecular and
cellular level, the variability between populations of the same species and, indeed,
between different species will allow us to construct population-scale models of the
fundamentally important geochemical processes of calcification. These will allow us to
understand how coccolithophore populations may adapt to predicted changes in ocean
chemistry that will inevitably occur over the coming decades to centuries.
References
BROWNLEE C., TAYLOR A.R. (2005) - Calcification in coccolithophores: a cellular perspective.
In: H. Thierstein, J. Young (eds), Coccolithophores: from molecular processes to global impact.
Springer, Berlin: 31-50.
41 st S.I.B.M. CONGRESS Rapallo (GE), 7-11 June 2010
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