Dissolution of Fe(III)-rich basaltic glass in microbial cultures of iron-reducing microorganisms

The aim of this study was to investigate the contribution of Fe(III)-reducing microorganisms to the dissolution rates of Fe(III)-rich synthetic basaltic glass. Hyperthermophilic archaeon Pyrobaculum islandicum and thermophilic bacterium Thermus scotoductus were incubated for 7 or 15 days with basaltic glass, and the surface retreat of the glass was determined using vertical scanning interferometry. Pyrobaculum islandicum was shown to enhance basaltic glass dissolution rate two-fold compared to abiotic controls in 7-days incubations. However, this effect was only 1.3-fold in 15-days incubations. In contrast, Thermus scotoductus did not impact or slightly inhibited the dissolution. Accordingly, alteration microstructures of the surface were visible only with Pyrobaculum islandicum cultures which promoted the formation of (Al, P, S)-rich layers thickening with time at the surface of the glass as well as of (Fe, S)-bearing crystals. To identify the underlying mechanisms that could explain such differences, Fe(III) reduction assays were performed in cultures with Fe(III) citrate, revealing higher rates of Fe(III) reduction in incubations with Pyrobaculum islandicum compared to those with Thermus scotoductus. Collectively, these findings suggest that Fe(III)-reducing microorganisms can enhance basaltic glass dissolution, but that the process could be limited by the rate of Fe(III) reduction and by surface alteration products.