Extremely Thermoacidophilic Metallosphaera Species Mediate Mobilization and Oxidation of Vanadium and Molybdenum Oxides

Certain species from the extremely thermoacidophilic genus directly oxidize Fe(II) to Fe(III), which in turn catalyzes abiotic solubilization of copper from chalcopyrite to facilitate recovery of this valuable metal. In this process, the redox status of copper does not change as it is mobilized. species can also catalyze the release of metals from ores with a change in the metal's redox state. For example, catalyzes the mobilization of uranium from the solid oxide U O , concomitant with the generation of soluble U(VI). Here, the mobilization of metals from solid oxides (V O , Cu O, FeO, MnO, CoO, SnO, MoO , Cr O , Ti O , and Rh O ) was examined for and at 70°C and pH 2.0. Of these oxides, only V and Mo were solubilized, a process accelerated in the presence of FeCl However, it was not clear whether the solubilization and oxidation of these metals could be attributed entirely to an Fe-mediated indirect mechanism. Transcriptomic analysis for growth on molybdenum and vanadium oxides revealed transcriptional patterns not previously observed for growth on other energetic substrates (i.e., iron, chalcopyrite, organic compounds, reduced sulfur compounds, and molecular hydrogen). Of particular interest was the upregulation of Msed_1191, which encodes a Rieske cytochrome fusion protein (Rcbf, referred to here as V/MoxA) that was not transcriptomically responsive during iron biooxidation. These results suggest that direct oxidation of V and Mo occurs, in addition to Fe-mediated oxidation, such that both direct and indirect mechanisms are involved in the mobilization of redox-active metals by species. In order to effectively leverage extremely thermoacidophilic archaea for the microbially based solubilization of solid-phase metal substrates (e.g., sulfides and oxides), understanding the mechanisms by which these archaea solubilize metals is important. Physiological analysis of species growth in the presence of molybdenum and vanadium oxides revealed an indirect mode of metal mobilization, catalyzed by iron cycling. However, since the mobilized metals exist in more than one oxidation state, they could potentially serve directly as energetic substrates. Transcriptomic response to molybdenum and vanadium oxides provided evidence for new biomolecules participating in direct metal biooxidation. The findings expand the knowledge on the physiological versatility of these extremely thermoacidophilic archaea.