Calcification of selected coccolithophore species: meabolic state and trace metal partitioning
Zusammenfassung der Projektergebnisse
Nitrogen is one of the most abundant nutrient after C and plays a critical role in physiology, being an essential component of protein and nucleic acids. The N availability substantially affects the acquisition of inorganic carbon (Ci) by algae by modulating the photosynthetic affinity for Ci and the activity of the CO2 concentrating mechanism (CCM). The N source and the availability of Ci have a strong influence on the way resources are partitioned and allocated in algal cells. In more detail, nutrient deprivation (especially N and C) can induce the allocation of resources towards specific metabolic pathways; these responses are regulated at both pre- and post-translational level. Some of the many questions are: What are the intracellular processes that define the C to N ratio in a common phytoplankton cell? What determines the relative composition of macromolecular pools within the cells? Can we find quantitative descriptions of the most relevant processes that can be used in mathematical models of the phytoplankton growth? For this project, the coccolithophore Emiliania huxleyi was chosen. This organism provides an important contribution to the marine primary production and it is considered to be one of the major producers of calcite in the ocean. The primary aim of this project was to contribute to the understanding of carbon and nitrogen metabolic interaction in Emiliania huxleyi and to provide new insights on the allocation of resources within the cells. In this project, we combined traditional biochemical methods with innovative spectroscopic methods (FTIR). In order to develop a process understanding of the regulation of particulate cellular chemical composition (C/N homeostasis), we determined the kinetic properties of a variety of key enzymes controlling the cellular nitrogen fluxes (nitrate reductase, nitrite reductase, glutamine synthase, glutamate oxoglutarate aminotransferase). The cellular carbon fluxes (Photosynthesis, Respiration, and the uptake rates of inorganic carbon species), we measured with a membrane inlet mass spectrometer. In order to understand how resources are allocated within the cells under the different growth conditions, the relative size of the macromolecular pools (protein, carbohydrates, lipids) were estimated with FTIR spectroscopy. The study of pool variations were complemented with traditional measurements of cell particulate C:N composition. The growth rates and C to N ratios seems to be not altered by the nitrate availability (range: 10 µM – 280 µM). This finding is surprising since the kinetic properties of the enzymes involved in the C and N assimilation pathway as well as the allocation of resources to the macromolecular pools were sensitive to a change in the growth conditions. The data suggest that a concerted regulation of the intracellular CO2 and NO3 concentrations is required to maintain balanced C and N metabolic fluxes resulting in a constant C to N ratio. In this project, the experiments have been planed and conducted in close communication with the needs of the modeller. With the data set developed in this project, it will be possible to apply detailed modelling to interpret experimental results and to predict the dynamic behaviour of cells under changing environmental conditions and in the consequences of specific genetic changes. This straightforward type of modelling means translating the biochemistry into mathematics. The limitation of this kind of approach for most systems, however, is the fact that complete data sets of good quality are more the exception than the rule. The overall aim of this project was to improve the data situation for Emiliania huxleyi.
Projektbezogene Publikationen (Auswahl)
- “Barium partitioning in coccoliths of Emiliania huxleyi”. (2009). Geochimica et Cocmochimica Acta, 73(10), 2899 - 2906
Langer, G., Nehrke, G., Thoms, S., Stoll, H.
- “Carbon and nitrogen fluxes in the marine coccolithophore Emiliania huxleyi grown under different nitrate concentrations”. (2010), PhD Thesis, Jacobs University Bremen
A. Kaffes
- “Carbon and nitrogen fluxes in the marine coccolithophore Emiliania huxleyi grown under different nitrate concentrations”. (2010). Journal of Experimental Marine Biology and Ecology, 393(1-2), 1-8
Kaffes, A., Thoms, S., Trimborn, S., Rost, B., Langer, G., Richter, K-U., Köhler, A., Norici, A., Giordano, M.
