Microbes as geologic agents: Their role in mineral formation

Laboratory and in situ studies have revealed that microbes play a role in some cases of mineral formation. Microbes may form minerals authigenically or diagenetically. The minerals may appear external to the microbial cell responsible for its genesis, on or in the cell envelope, or within the cell. Some microbial mineral formation is active and may involve direct enzymatic intervention or metabolic production of specific chemical reactants that cause precipitates to form. Other microbial mineral formation is passive and may even be mediated by dead cells. In the environment, microbial mineral formation is a form of immobilization of chemical elements and can be a form of detoxification. In this paper examples of these various forms of microbial mineral formation and the sites at which these minerals are deposited by different microorganisms are discussed.