METHANOBACTIN-PROMOTED DISSOLUTION OF CU-SUBSTITUTED BOROSILICATE GLASS

Mineral weathering processes play a major role in the global cycling of carbon and metals and there is an increasing realization that subsurface microbial activity may be a key factor regulating specific biogeochemical reactions and their rates. Methanobactin (mb) is an extracellular copper-binding compound excreted by methanotrophs who require copper to regulate methane oxidation. Cu that is available to the cell regulates the expression and activity of pMMO versus sMMO (particulate versus soluble methane monooxygenase, respectively), which are key enzymes responsible for methane oxidation. The primary focus of this study is to determine the effect of mb-promoted dissolution of Cu-substituted glass at low temperature and near neutral pH conditions, using batch dissolution experiments with and without the methanotroph, Methylonsinus trichosporium OB3b. Methanobactin promotes the weathering of Cu-substituted borosilicate glasses at rates faster than control experiments without methanobactin. Glasses with lower concentrations of copper (80 ppm) or no copper are dissolved more rapidly than those containing larger amounts of copper (800 ppm). Within the first 2 hours of reactivity, a greater quantity of mb appears to sorb onto the glass surface at higher copper concentrations and may limit mass transfer of Cu to solution.  Furthermore gene expression in M. trichosporium OB3b, using real-time RT-PCR techniques, indicate that pmoA expression is influenced by mb in presence of Cu containing solid phases. These findings demonstrate that this methanotroph can directly access mineral-bound Cu and suggests that methane oxidation rates may be directly linked to mineral weathering in near-surface geologic settings.