An integrated approach to the study of biosignatures in mineralizing biofilms and microbial mats

In this thesis project, biomarkers, biomineralization processes and TREE (trace and rare earth elements) patterns in mineralizing microbial mats were established and tested as biosignatures in recent and fossil environments. To overcome limitations of conventional biomarker analysis, a comprehensive analytical approach was developed that accomplished the detection and the laterally resolved visualization of biomarkers on the same sample, and with minimal sample disruption. In a pilot experiment, the application of ToF-SIMS (time-of-flight secondary ion mass spectrometry) enabled the simultaneous analysis of major archaeal biomarker classes in calcifying microbial mats from the Black Sea. ToF-SIMS has a strong potential for molecule detection, identification and visualization at the microscopic range. However, because the method is still in its infancy with respect to the analysis of organic biomarkers, further evaluations of capabilities and limitations are required. To furt! her expand the range of biomarker reference standards, ToF-SIMS spectra of selected glycerolipids were obtained, and the formation of molecular ions and specific fragments was studied in detail. Based on the reference data, it was possible to identify lipids (diglycerides and phosphatidylglycerol) in microscopic sections of mineralizing microbial mats from Black Sea methane seeps, and from Gallionella ferruginea-dominated iron-oxidizing microbial mats from the Aspo Hard Rock Laboratory (HRL). G. ferruginea mats were also investigated to study biomineralization processes and corresponding TREE fractionations as potential biosignatures for microbially induced formation of iron oxyhydroxides. For that purpose, a long-term flow reactor experiment was established in the Aspo HRL. Biomineralization processes and concomitant TREE accumulation within theses microbial mats revealed different forms of biomineral formation during growth and aging of G. ferruginea and massive, up t! o 106 fold accumulations of individual metals. In a third experiment, a comprehensive analytical approach to biosignatures within fracture minerals in the ~1.8 Ga old Aspo Diorite enabled the reconstruction and integrated understanding of ancient environmental processes that occurred within the deep continental biosphere. ToF-SIMS, CRM (Confocal Raman Microscopy), LA-ICP-MS (laser ablation-inductively coupled mass spectrometry) and respectively electron microprobe and isotope sampling analyses were performed on two, 5 mm thick opposing rock sections, i.e. on a minute amount of fracture minerals, which enabled to retrace four different fracture mineral generations. One of them, an organic-rich amorphous layer, exhibited numerous functionalized organic molecules and accumulations and fractionations of distinct TREE and was interpreted as a fossilized biofilm. Biofilm formation was most probably induced by glacially induced fracture reactivation and water injections down to 450 m depth. Further fracture mineral formation ! terminated and entrapped the microbial activity that once occurred at depth. The integrated approach used in this study led to the successful establishment of source specific biosignatures, and offers a strong tool kit for the study of mineralizing microbial mats and their interaction with the environment. The techniques employed in this study may further help to link biosignatures in recent systems to their fossil analogues and ultimately, to early complex forms of life. It can be foreseen that high resolution techniques such as ToF-SIMS and CRM will grow in importance not only in geobiology, but in all fields of natural sciences, wherever the detection and precise localization of organic compounds in environmental materials is required.