Laboratory evidence for microbially mediated silicate mineral dissolution in nature

Bacteria may potentially enhance or inhibit silicate mineral dissolution in nature by a variety of mechanisms. In the laboratory, some microbial metabolites enhanced dissolution rates by a factor of ten above the expected proton-promoted rate by an additional ligand-promoted mechanism focussed principally at Al sites at the mineral surface. In investigations with bacteria, it was found that organic acids are produced in organic-rich/nutrient-poor cultures, resulting in increased mineral dissolution rates compared to abiotic controls. Alginate and poly-aspartate inhibited dissolution rates either by a reduction in surface reactivity or reactive surface area (or both). Bacteria may also influence dissolution rates by creating and maintaining microenvironments where metabolite concentrations are higher than in the bulk solution.