COMBINED STXM AND TEM STUDIES OF GEOMICROBIOLOGICAL SAMPLES

I started my postdoc with Gordon E. Brown Jr as an electron microscopist and a geomicrobiologist. I expanded significantly my skills in microscopy by using extensively Scanning Transmission X-Ray Microscopy on samples of environmental and geomicrobiological significance. I will review how the systematic combination we did of Scanning Transmission X-ray Microscopy (STXM) and Transmission Electron Microscopy (TEM) allowed to perform high spatial and energy resolution near-edge x-ray absorption fine structure (NEXAFS) and high resolution imaging on diverse samples of geomicrobiological interest. I will consider diverse samples including naturally and experimentally biomineralized bacteria, pathogenic calcification, metamorphosed fossils and bioweathered silicates. I will show how spectroscopy was performed at the C K-edge, Al K-edge, Ca L2,3-edge, Fe L3-edge, and N K-edge offering the possibility to characterize diverse biochemical compounds, unique bacterial spectroscopic signatures, and iron oxidation state at microorganism-mineral interfaces. Combination of TEM and STXM provides remarkably clear chemical state-specific images of fossilized microorganisms and microorganism-mineral interfaces at the nanometer scale and 0.1-0.3 eV energy resolution. The methodology presented here should be helpful in assessing the importance of microorganisms in the evolution of Earth's surface chemistry and in identifying them in early Earth and planetary materials.