Enhancement of kaolinite dissolution by an aerobic Pseudomonas mendocina bacterium

This research focused on whether bacteria living in aerobic environments where Fe is often a limiting nutrient could access Fe associated with the clay mineral kaolinite. Kaolinite is one of the most abundant clays at the Earth's surface, and it often contains trace quantifies of Fe as surface precipitates, accessory minerals, and structural substitutions. We hypothesized that aerobic bacteria may enhance kaolinite dissolution as a means of obtaining associated Fe. To test this hypothesis, we conducted microbial growth experiments in the presence of an aerobic Pseudomonas mendocina bacteria that is incapable of using Fe as a terminal electron acceptor for oxidative phosphorylation and that requires only muM concentrations of Fe, for metabolism. We determined that the presence of kaolinite allowed the bacteria to grow above levels of nonkaolinite-containing controls, in Fe-limited conditions. We further demonstrated that the bacteria significantly enhanced Al- and Si-release from the kaolinite. These results indicate that clays that contain even trace quantities of Fe need to be considered as additional sources of Fe in aerobic environments and suggest that microbial processes may exert important, but until now largely overlooked. influences on the dissolution rates of clays.