Biomineralization in cysts of flagellated microalgae

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Biomineralization the formation of complex inorganic materials by biological processes, is a widespread phenomenon. The minerals formed are inorganic/organic composite materials (biomaterials) with highly controlled macro- and nanostructured mineral phases that provide them with multifunctional properties. Beautiful examples of biomaterials occur in unicellular, eukaryotic microalgae; the focus of the proposal. Flagellated microalgae represent a major group of plankton. Among these, dinoflagellates with about 2000 living species constitute one of the largest groups. Many coastal species are associated with harmful algal blooms which occur in summer. Because of the production of neurotoxins these blooms may result in massive death of fish, mussels, and other forms of marine life. Humans may be poisoned by eating animals containing these toxins, what is called paralytic shellfish poisoning. For this reason there is a strong ecological interest in learning more about the complex life cycle of dinoflagellates. The life-cycle usually involves asexual cell division, but sexual reproduction also occurs. More than 10% of the dinoflagellate species produce (mineralized) resting stages, called dinoflagellate cysts, as part of their life cycle. Furthermore cysts of several dinoflagellate species exhibit organic walls or calcareous and sometimes even siliceous walls. Calcareous resting cysts are composed of calcite and an inner organic layer supports the calcareous ornamentation.Although dinoflagellate cyst structures are known to paleogeologists, the biomineralization processes in dinoflagellates have not been investigated despite the fact that dinoflagellates are the second most abundant calcareous phytoplankton group. Furthermore, dinoflagellates are an extremely promising model system for biomineralization since they can easily be cultivated or isolated from sediments. Cyst formation be easily induced in culture by nutrient depletion or change of temperature and light irradiation. Recently, fossilized calcite-cysts were shown to have extremely interesting, interwoven fibre-like structures. These very special, basket-like structures constitutes a novel type of calcite biomineral architecture. These structures so far observed only in fossil cysts raises numerous questions concerning biomineral formation in living dinoflagellate cysts. At the moment, neither the detailed structure/function relations, nor the formation and stabilization mechanism of the mineral phase are known. The aim of the planned research is therefore, to investigate the biomineralization processes in dinoflagellates during their complex life cycle, especially the structure formation mechanisms and the interactions between the organic material and the mineral phase, particularly the calcium carbonate. For the study of freshly cultured mineralized cyst structures the use of analytical methods like Cryo-SEM, FIB-SEM, FT-IR and Micro-Raman spectroscopy is proposed.