Quantitative mapping of toxic metals on the submicron-scale in cell-mineral aggregates formed by iron mineral precipitating and dissolving bacteria

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The distribution, mobility and bioavailability of toxic trace metals such as Cr, Co, Ni, Cu, Zn, As, Cd, Hg, and Pb in natural and contaminated environments are often controlled by the sorption to organic biomacromolecules and by the sorption to and co-precipitation with (bio-)minerals, in particular Fe-minerals. Chemical micro- and submicro-environments with steep geochemical gradients control speciation and stability of the involved phases. The influence of the submicron-size heterogeneity and chemical micro-niches of complex environmental biofilm-mineral aggregates on the speciation and partitioning of toxic trace metals will be studied in hydrated, close-to-natural environments at the spatially relevant scale using synchrotron-based scanning transmission X-ray microscopy (STXM) which combines near edge X-ray absorption fine structure (NEXAFS) based speciation sensitivity with ≤ 30 nm spatial resolution. 2D and 3D-tomographic STXM will be optimized to allow for the in-situ analysis of the speciation of major organic macromolecules and the associated metals and minerals. The speciation and partitioning of Ni, Cu and Zn between well-analyzed bacterial model strains, their exopolymers and associated Fe-biominerals will be studied under chemically well controlled conditions. Finally, metal speciation and partitioning will be quantified and mapped in both pristine and anthropogenically influenced environmental systems. The combination with confocal laser scanning microscopy using specific fluorescence dyes and probes will be used for up-scaling the STXM results and further characterizing the exopolymers.