Preservation of bacterial microfossils of Fe-oxidizing bacteria during diagenesis of sedimentary deposits, i.e. banded iron formations

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Precambrian sedimentary deposits such as banded iron formations (BIFs) are in the focus of researchers who aim to understand early life and its relevance for the evolution of the earth’s atmosphere. Iron-oxidizing bacteria are believed to be involved in the formation of Precambrian BIFs. The main goal of this project is to study on the laboratory scale diagenesis processes of cell-mineral aggregates and in particular to identify and quantitatively map structural and (organo-) chemical features on the micron- / submicronscale which are indicative of bacterial life. To this end experiments are planned with cellmineral aggregates of several model strains of laboratory cultures of Fe-oxidizing bacteria. Cell-mineral aggregates will be exposed to systematically increasing temperatures and pressures up to the conditions typically experienced by Precambrian BIFs. An appropriate set of correlative analytical microscopies will be determined. Samples will be prepared by conventional ultramicrotomy and focused-ion beam (FIB) milling for qualitative and quantitative analytical electron and soft X-ray spectromicroscopy studies to investigate both morphology and (organo-) chemical fingerprints of the bacterial residues. Additionally the 3D structure of the residues will be mapped by FIB-tomography. Infrared Spectromicroscopy and confocal Raman microscopy will provide further chemical information at moderate spatial resolution. The results from three different types of biogenic Fe-minerals (from encrusting, non-encrusting and stalk/sheath-forming bacteria) will be compared with regard to their potential for the preservation of bacterial microfossils.