- © The Mineralogical Society Of America
Bacteria are small, prokaryotic, microorganisms that are ubiquitous in surface and subsurface terrestrial and aquatic habitats. Prokaryotes comprise two Domains (Superkingdoms) in the biological taxonomic hierarchy, the Bacteria and the Archaea. They exhibit remarkable diversity both genetically and metabolically even within the same microenvironment and they are thought to play a major role in the deposition and weathering of minerals in the earth’s crust. The synthesis of minerals by prokaryotes can be grouped into two canonical modes: 1) biologically induced mineralization (BIM) and 2) biologically controlled mineralization (BCM) (Lowenstam 1981; Lowenstam and Weiner 1989). In this chapter, we focus on biologically induced mineralization.
Minerals that form by biologically induced mineralization processes generally nucleate and grow extracellularly as a result of metabolic activity of the organism and subsequent chemical reactions involving metabolic byproducts. In many cases, the organisms secrete one or more metabolic products that react with ions or compounds in the environment resulting in the subsequent deposition of mineral particles. Thus, BIM is a presumably unintended and uncontrolled consequence of metabolic activities. The minerals that form are often characterized by poor crystallinity, broad particle-size distributions, and lack of specific crystal morphologies. In addition, the lack of control over mineral formation often results in poor mineral specificity and/or the inclusion of impurities in the mineral lattice. BIM is, in essence, equivalent to inorganic mineralization under the same environmental conditions and the minerals are therefore likely to have crystallochemical features that are generally indistinguishable from minerals produced by inorganic chemical reactions. In some cases, the metabolic products diffuse away and minerals form from solution. However, bacterial surfaces such as cell walls or polymeric materials (exopolymers) exuded by bacteria, including slimes, sheaths, or biofilms, and even dormant spores, can act as important sites for the adsorption of ions …