Exploring reaction mechanisms of dissimilatory ferric reduction-coupled sulfur oxidation (DIRSO) by acidophilic prokaryotes and its relevance for bioleaching and acid mine drainage formation

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Bioleaching processes and acid mine drainage (AMD) generation are mainly driven by microbial aerobic iron and sulfur oxidation, and they are also greatly influenced by microbial dissimilatory iron reduction coupled to sulfur oxidation (DIRSO) which has been described for anaerobic as well as aerobic conditions at very low pH. Studies in DIRSO by acidophiles are rare, and these focused on mesophilic acidophiles but hardly on thermophilic acidophiles. Moreover, a lack of knowledge exists for DIRSO-related iron and sulfur speciation transformation, microbial community structure and function and the molecular mechanism of iron and sulfur metabolic pathways in acidophiles, especially in thermoacidphiles. The proposed research project aims to explore the physiology and (bio)chemistry of DIRSO by thermoacidophilic archaea and mesoacidophilic bacteria. Microbe mineral interactions with different ferric iron containing minerals and different sulfur compounds will be studied by well-defined laboratory experiments with pure cultures including novel isolates, defined mixed cultures as well as microbial communities from acidic environments. High-end analytic techniques such as synchrotron radiation-based techniques (XANES, SR-XRD, STXM), online Raman spectroscopy, HPLC among others, will be applied to identify and quantify intermediary, labile chemical compounds involved in the Fe-S-coupled redox reactions in solution and on mineral surfaces. By detecting the sulfur-compound intermediates we will be able to describe reaction pathways of DIRSO in described and novel meso- and thermoacidophiles. At the same time, we will explore the microbial community structure and functional succession during leaching process and elucidate the iron/sulfur metabolic pathways of thermophilic acidophiles by transcriptomics and comparative proteomics. Towards application, DIRSO will be investigated in aerobic-anaerobic coupling systems by varying pH, electron donor (reduced sulfur compounds) and different ferric iron minerals for studying reaction kinetics in order to improve bioleaching and to better predict AMD generation.