Methanobactin-promoted dissolution of Cu-substituted borosilicate glass

Mineral weathering plays an important role in the global cycling of carbon and metals and there is an increasing realization that subsurface microbial activity may be a key factor controlling specific biogeochemical reactions and their rates. Methanobactin (mb) is an extracellular copper-binding compound excreted by methanotrophs to acquire copper for the regulation of methane oxidation. Bioavailable Cu regulates the expression and activity of pMMO vs. sMMO (particulate vs. soluble methane monooxygenase, respectively), key enzymes responsible for bacterial methane oxidation. In this study, we investigate the effect of mb on the dissolution of Cu-substituted borosilicate glass at low temperature and near neutral pH conditions, using batch dissolution experiments. Methanobactin promotes the dissolution of Cu-substituted glasses at rates faster than control experiments. Glasses with lower concentrations of copper (80 p.p.m.) or no copper are dissolved more rapidly by mb than those with more abundant copper (800 p.p.m.). Within the first 2 h of reaction, mb sorption onto glass surfaces limits mass transfer of Cu into solution, and at higher concentrations (100 µmol) of the ligand, inhibits dissolution rates of all glass formulations. These results suggest that both the concentration of mb in solution and the solid phase Cu concentration impact silicate weathering rates and related cycling of carbon in near-surface geological settings.