LITHOSPHERE-BIOSPHERE INTERACTIONS: IMPACTS OF ANTARCTIC ENDOLITHIC MICROBIAL COMMUNITIES ON WEATHERING OF SEDIMENTARY ROCK

We have used environmental scanning electron microscopy (ESEM) together with Energy Dispersive X-ray Spectroscopy (EDS) to examine cross-sectional profiles of quartzite rocks hosting layered endolithic microbial communities. These techniques allowed us to determine textural alterations of minerals by the organisms, microbial morphology, and elemental distributions in host rock vs organisms and with depth. In addition, we examined the same transect of the same sample by fluorescence microscopy using deep-ultraviolet laser excitation of 224 nm. Our ESEM-EDS results showed that different regions of rock–the outer weathering rind, uncolonised mineral, microorganisms, formerly colonised and weathered mineral-- had unique elemental compositions which corresponded to unique morphological and textural features. Graphical profiles of physiologically vital elements (Ca, Cl, K) by EDS closely matched biomass measurements made of UV-induced fluorescence. The microbial cells, most obvious as filaments, were covered by extracellular polymers (“slime”) which served as a site for metal accumulation and formation of fine-grained minerals with a clay-like morphology. These coatings showed a high silicon content. As the amount of biomass trailed off with depth in the rock, microbial filaments were progressively more silicified until only “fossils” were left. Our study allowed us to have a unique insight into processes of mineral dissolution and redistribution of trace elements (i.e., weathering) in a setting where the spatial contact between minerals and biota is maximised relative to other settings such as soils and sediments.