Experimental Interactions Between Clay Minerals and Bacteria: A Review

Interactions between microbes and minerals have the potential to contribute significantly to global cycles of various processes and serve as a link between the geosphere and life. Clays and clay minerals occur commonly in agriculturally utilized soils, are naturally grown underground (soil and rock) and are used in construction material. Clay minerals serve as natural, geological and technical barriers in geotechnics and environmental geotechnics. Bacteria in turn are ubiquitous in natural soils, subsoils and rocks and are in permanent contact with clay minerals. There are numerous ways in which bacteria can interact with clay minerals and alter them: dissolution, refinement and transformation, reduction of trace elements incorporated in the clay minerals and uptake of trace elements from these minerals, e.g., by the production of siderophores and chelators and enhancement or reduction of adsorbance of trace elements on clay minerals. In addition, bacteria can influence layer charge, cation exchange capacity (CEC), exchangeable cations, Brunauer–Emmett–Teller surface, swelling and the rheological properties of clay minerals. The field of clay mineral–microorganism interaction is still wide open because of the large potential that the interactions of bacteria with clay minerals in soils and sediments may result in changes in clay mineral properties and behaviors. Further detailed studies on all these tentative changes and underlying mechanisms as well as broad surveys of quantifications of extents and rates of clay mineral–microorganism interactions, especially in mimicking natural systems, are highly required. This review summarizes the influences of various bacteria on the properties of different clay minerals as determined experimentally using viable bacteria.