Details of Award
NERC Reference : NE/T000848/1
Assessing how cell size constrains carbon uptake in diatoms using direct measurements of cell surface carbonate chemistry
Grant Award
- Principal Investigator:
- Dr G Wheeler, Marine Biological Association, Marine Biology
- Co-Investigator:
- Professor C Brownlee, Marine Biological Association, Marine Biology
- Co-Investigator:
- Professor T Mock, University of East Anglia, Environmental Sciences
- Grant held at:
- Marine Biological Association, Marine Biology
- Science Area:
- Earth
- Marine
- Overall Classification:
- Panel C
- ENRIs:
- Biodiversity
- Environmental Risks and Hazards
- Global Change
- Science Topics:
- Biochemistry & physiology
- Microbial photosynthesis
- Biogeochemical Cycles
- Environmental Microbiology
- Responses to environment
- Plant responses to environment
- Abstract:
- The diatoms are a group of unicellular algae that represent some of the most important photosynthetic organisms on our planet. Diatoms are particularly abundant in nutrient rich coastal regions where they form the base of the food web, supporting fishing and seafood industries. It is estimated that diatoms contribute up to 20 % of global photosynthesis. It is therefore surprising that there are major uncertainties relating to the form of carbon taken up by diatoms and how these mechanisms are influenced by the size of the cell. Diatoms range from very small to very large (5-200 micrometre diameter) and can even form colonies, in the form of chains of cells linked together. This huge diversity in size has a major influence on the ability of each species to acquire nutrients from its environment, with the supply to larger species potentially limited by their diffusive boundary layer. Understanding how cell size constrains nutrient acquisition is therefore central to our understanding of diatom ecology and the distribution of different species, although direct measurements of the diffusive boundary layer around cells are lacking. Although seawater contains a plentiful supply of dissolved inorganic carbon, only a small proportion of this is present as carbon dioxide (CO2). The supply of CO2 to the cell by diffusion is therefore not sufficient to support the high rates of photosynthesis observed in diatoms. This problem is much greater in large species, due to the significant diffusive boundary layer around the cell surface. Diatoms, and other marine phytoplankton, therefore have to utilise the pool of bicarbonate (HCO3-), either by actively transporting it across the membrane or by using an enzyme (extracellular carbonic anhydrase) to catalyse its conversion to CO2, which can then diffuse across the membrane. However, it is technically difficult to measure the proportion of carbon taken up by these different mechanisms and different diatom species show considerable variability. Moreover, the role of the enzyme extracellular carbonic anhydrase has been much disputed. Because of this uncertainty, we do not have a mechanistic understanding of how changes in CO2 supply can influence the composition of diatom communities. With the concentration of CO2 in seawater predicted to change dramatically in the coming centuries, this uncertainty hampers our ability to predict how different species may respond to the changing availability of CO2. Improved knowledge of the microenvironment around diatom cells is necessary if we are to understand how they acquire carbon from seawater. We have developed tiny ion-selective microelectrodes that can be placed at the surface of a single diatom cell. By measuring pH and carbonate (CO32-), we can calculate fluxes of carbon across the membrane and estimate to what extent the supply of CO2 to the cell surface may be limiting. This project will use these new techniques to address some of the major questions relating to carbon acquisition by diatoms. We wish to examine the extent to which CO2 supply is limiting to cells of different sizes and examine how mechanisms of carbon uptake are adjusted to cope with changes in carbon supply (e.g. elevated CO2) or carbon demand (e.g. a greater rate of carbon fixation is needed at high light). We will also examine whether the supply of CO2 influences the ability of certain species to form chains, in order to understand the environments where we might expect these species to be successful. These studies using microelectrodes will be complemented by a molecular genetic approach to study to the role of the enzyme, extracellular carbonic anhydrase, which appears to play a critical role in the supply of CO2 to some diatoms. Finally, we will also examine natural populations of diatoms to see how they are influenced by changes in the availability of carbon dioxide throughout the progression of a typical diatom bloom.
- NERC Reference:
- NE/T000848/1
- Grant Stage:
- Completed
- Scheme:
- Standard Grant FEC
- Grant Status:
- Closed
- Programme:
- Standard Grant
This grant award has a total value of £556,443
FDAB - Financial Details (Award breakdown by headings)
| DI - Other Costs | Indirect - Indirect Costs | DA - Investigators | DI - Staff | DA - Estate Costs | DI - T&S | DA - Other Directly Allocated |
|---|---|---|---|---|---|---|
| £78,791 | £124,570 | £78,613 | £189,877 | £73,252 | £10,650 | £689 |
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