Phytoplankton
Marine phytoplankton have major influences
on the oceanic carbon and nutrient cycles. We study the cell biology of
two major classes of phytoplankton, the diatoms and coccolithophores that
have very different physiological characteristics. This work aims
to provide a basic understanding of the specific adaptations of different
species to environmental conditions that allow them to grow and compete
in the fluctuating and seasonal marine environment. These differences are
manifest as dramatic seasonal succession patterns in temperate waters.
Phytoplankton growth may be limited by light, nutrients and inorganic carbon.
We are particularly interested in carbon and nutrient acquisition pathways
across the plasma membrane. With respect to carbon acquisition, different
species appear to have evolved different mechanisms for overcoming the
low levels of CO2 available for photosynthesis in the sea.
Coccolithophores
Coccolithophores represent a unique group of phytoplankton that produces calcium carbonate scales (coccoliths: visit the CODENET site for detailed taxonomic descriptions of coccolithophores within specialized intracellular compartments. These are secreted to the surface of the cell where they form an outer coat or coccosphere. We are currently studying two aspects of calcification. Firstly, the production of calcium carbonate results in the production of protons production of protons . We are investigating whether this production has a metabolic role such as facilitating CO2 production or whether protons represent a waste product that needs to be rapidly removed from the cell. Secondly, the large trans-cellular fluxes associated with calcification pose particular problems for maintaining calcium homeostasis in the cytoplasm while allowing calcium to be used as an intracellular signal. We are currently studying the pathway for calcium transport into the coccolith-forming compartment using a range of approaches. These include EM imaging and elemental analysis, biochemical studies of calcium-binding proteins, confocal fluorescence imaging of intracellular pH and measurements of photosynthesis and chlorophyll fluorescence. Electrophysiological studies of the coccolithophore plasma membrane carried out in collaboration with Dr. Alison Taylor are shedding light on the membrane transport processes involved in calcification and are beginning to uncover several unique features of membrane transport in coccolithophores.
We are making use of emerging genome sequence data for Emiliania huxleyi to identify membrane transporters, ion channels and other components of the calcification pathway and regulatory mechanism. Our longer term aim to achieve functional characterization of these components. Aspect of this work are being carried out in collaboration with partners in the Leverhulme International Academic Collaboration on Molecular Biology of Emiliania huxleyi.
Diatoms
In collaboration with Dr. A.R. Taylor we have begun to elucidate the molecular nature of specific diatom transporter proteins in the plasma membrane. This project is funded through the EU-funded DIATOMICS Strategic Targetted Research Programme. Our role in programme is the functional characterization of membrane transport and related genes involved in carbon and nutrient acquisition and intracellular signalling. The DIATOMICS programme comprises 14 European partners and is part of an international diatom genomics consortium which is using the data generated by diatom genome sequencing projects (Thalassiosira pheudonana and Phaeodactylum tricornutum) to gain an understanding of the key physiological processes that underlie diatom ecophysiology.
