Raman spectroscopic study of biogenic crystals of sulphate and phosphate complexes with alkaline earth metals present in microorganisms

Annotation: Many microorganisms contain a variety of crystalline inclusions, including biogenic minerals. One important group is represented by the microcrystals of celestite (SrSO4) and barite (BaSO4) identified in some freshwater and marine microorganisms. Their function is not fully understood. Although the concentration of strontium and barium in the environment is significantly lower than the concentration of calcium, some microorganisms are able to selectively accumulate these elements in remarkable amounts, even in excess of calcium, and store them inside their cells as insoluble sulphates. Under artificial conditions, where it is possible to control the concentration of Ca, Ba and Sr, the formation of biogenic mixed crystals of different stoichiometry can be achieved, which can be characterized directly in the cells by Raman microscopy. The second interesting group is represented by insoluble complexes of some divalent metals with phosphates, especially pyrophosphates and polyphosphates. Polyphosphates are known to have a number of important biological functions. Pyrophosphates can be formed as a product of ATP cleavage. In both cases, information on the stoichiometry of cations in the complexes obtained spectroscopically in-situ could contribute to a better understanding of their functions. The subject of the diploma thesis will be to find spectral markers enabling to determine the chemical composition of these biogenic crystals by using Raman microscopy. The researcher prepares a series of synthetic samples with a known stoichiometric ratio, measures their Raman spectra and determines the relationship between spectral characteristics and stoichiometry. The results will be used to determine stoichiometry in biogenic microcrystals of microorganisms. Experimental equipment and necessary material are available. The diploma thesis will be a part of the grant project of the Czech Science dipFoundation, from which the researcher will be provided with financial support.