Towards the investigation of microbe-mineral interaction by means of Raman spectroscopy

The aim of this doctoral thesis is to gain more information about the interaction processes which take place in nature between the biotic and abiotic components. The ultimate goal is to be able to increase the bioremediation rate by modifying accordingly the factors which influence the bioremediation. To be able to reach this goal, detailed studies focused on biomineralization, biotransformation and biodissolution are required. The influences of various geochemical factors on the microbial communities of an environment, and the response of microorganisms to those factors have to be studied. Furthermore, information regarding the identity of the microorganisms forming the microbial consortium and their role played in the investigated environment is imperatively necessary. Previous investigations have shown that bulk and single cell bacterial identification is doable by means of Raman spectroscopy. In addition, Raman spectroscopy can be used for identification of minerals, organic matter, liquids or gases presented in the rocks. The high sensitivity, the minimal sample preparation and the possibility to investigate minerals instable at atmospheric conditions makes Raman spectroscopy a valuable tool for the investigation of the minerals. The interaction between the biotic and the abiotic components of an iron contaminated aquatic environment was the main topic of this doctoral thesis . The investigation of the bacterial-mineral interactions implies two studies: the influence of the microbial communities on the mineral phases of the pelagic aggregates, and the effect of the geochemical conditions of the aquatic environment on the microbial consortia. In addition to these studies, investigation of biologically mediated iron-rich sedimentary rocks was also performed, emphasizing the potential application of Raman spectroscopy in the field of microbe-mineral interaction

Exploratory Monitoring of the Quality and Authenticity of Commercial Honey in Ecuador

Honey is one of the oldest sweetening foods and has economic importance, making this product attractive to adulteration with cheap sugars. This can cause a critical problem in the honey industry and a possible health risk. The present work has the aim of evaluating the authenticity of honey commercialized in two different provinces of Ecuador (Pichincha and Loja) by performing physicochemical and spectroscopic analyses. For this study 25 samples were collected from different places and markets and characterized by water, sucrose, reducing sugars and electric conductivity measurement. Also, their Raman and Infrared (IR) spectra were recorded and analysed using a Principal Component Analysis (PCA) in order to verify the quality of the honeys. In addition, a screening of several pesticides was performed in order to verify possible chemical threats to human health and honey bees. It was found that 8 samples have a deviation from the Standard established parameters. Two of them have a high difference in the content of sucrose and reducing sugars, which are located deviated from all the other samples in the PCA of the applied vibrational spectroscopy (IR/Raman), shaping two clear clusters. The results show that Raman and IR spectroscopy is appropriate techniques for the quality control of honey and correlates well with the physicochemical analyses.Centro de Química Inorgánic

STXM and NanoSIMS Investigations on EPS Fractions before and after Adsorption to Goethite

Extracellular polymeric substances (EPS) are expected to be an important source for the formation of mineral-organic associations in soil. Because such formations affect the composition of mobile and immobile organic matter as well as the reactivity of minerals, we investigated the composition of EPS before and after adsorption to goethite. Raman measurements on EPS extracted from <i>Bacillus subtilis</i> distinguished four fractions rich in proteins, polysaccharides, lipids, or lipids and proteins. Scanning transmission X-ray microscopy identified three different EPS-fractions that varied in their composition in proteins, nonaromatic proteins, and polysaccharides. Reaction of EPS with goethite led to a preferential adsorption of lipids and proteins. The organic coverage was heterogeneous, consisting of ∼100 × 200 nm large patches of either lipid-rich or protein-rich material. Nanoscale secondary ion mass spectrometry showed a strong S enrichment in aggregates of ∼400 nm in the goethite adsorbed EPS. From our simplified model system, we learned that only a small portion (<10%) of EPS was immobilized via adsorption to goethite. This fraction formed a coating of subμm spaced protein-rich and lipid-rich domains, i.e., of two materials which will strongly differ in their reactive sites. This will finally affect further adsorption, the particle mobility and eventually also colloidal stability