Chapter 12 : Bacterial Surface-Mediated Mineral Formation

Unstained transmission electron micrograph of a water sample from the Golden Giant mine tailings pond (Hemlo gold region, Marathon, Ontario, Canada) prepared by drying an aliquot of water onto a Formvar-carbon coated 200 mesh Cu-TEM grid and examined using a Philips EM300 electron microscope (a whole mount). Not all of these bacteria have precipitated fine-grained iron-arsenic minerals on their surface. Elemental analysis was performed using a Philips EM400T electron microscope equipped with a LINK X-ray analyzer for energy-dispersive X-ray spectroscopy (data not shown). The immobilization of metal on bacterial cell surfaces occurs at distinct nucleation sites, resulting in the development of fine-grained minerals. Bar, 1 µm.

Unstained, ultrathin section transmisison electron micrograph of a mineralized biofilm from the Copper Rand mine tailings pond (Chibougamou. Quebec. Canada), revealing an unmineralized bacterium, mineralized bacteria, and inorganic particulate material that has been trapped by the biofilm. The nonmineralized cell is presumably viable, containing a hydronium “cloud” produced by its proton motive force. The proton motive force creates an acidic environment at the bacterial cell surface and prevents or limits heavy-metal binding, while the other two cells probably exhibited little or no metabolic activity at the time of sampling and are mineralized. Bar, 0.5 µm.

Unstained, ultrathin-section transmission electron micrograph of a mineralized biofilm from the Lemoine tailings pond (Chibougamau, Quebec, Canada), demonstrating how capsular material is capable of protecting a bacterial micro-colony from mineralization. Bar, 0.5 µm.

Unstained ultrathin-section transmission electron micrograph of a Desulfotomaculum sp. which has been cultured in the presence of 100 ppm of Fe2+, resulting in the precipitation of amorphous FeS (reference 67 and data not shown). FeS precipitation at the cell surface is caused by the presence of HS−. released as a by-product of SRB metabolism, presumably forming an HS− rich microenvironment around the individual SRB. Even in active surface catalysis systems, the surface of the bacteria has an uneven distribution of minerals. Bar. 0.5 µm.

Unstained ultrathin-section transmission electron micrograph of an SRB culture/diagenesis system that has been incubated at 21°C for 6 months. Bacterial diagenesis promoted the nucleation of iron disulfide as a bilayer on the inner and outer surfaces of the SRB, representing the earliest and dominant stage of bacterial mineral diagenesis. Bar. 100 nm.