microbial mechanisms in biomineralization

Activities of microorganisms can lead to formation of biominerals. This biomineralization has been described to be either 'microbially controlled' or 'microbially induced'. The control over crystalization can work intracellularly, e.g. with magnetosomes, or extracellularly like in mammals. With increasing evidence for intermediate processes with specific proteins inducing different crystalloid (macro)morphology even at a distance to a colony, and processes involving both bioweathering and formation of new minerals, the concept of biomineralization should be re-visited and a more detailed classification of biomineralization processes is needed including formation of a stable backbone determining the macromorphology of biominerals even at distance from cell surfaces.

Here, the supply of mineral components (e.g. phosphate, reduced nitrogen compounds, etc.) through microbial exudation and matrix provided by bacteria or fungi are discussed. Especially with respect to metal resistance mechanisms, this is an active process, costly to the cells. Examples are given for microbial biomineralization processes in metal rich environments on  a former heap site. The formation of manganese hydroxides, like birnessite, leading to massive hardpan formation, is one of the examples derived from the former uranium mining site in Thuringia, Germany. Other examples with different macromorphologies include carbonates, (magnesium) calcite or vaterite, formed under laboratory conditions with strains of streptomycetes in dependence of excreted amphipathic surface proteins of the bacteria. And as a third example, the formation of (nickel) struvite, switzerite and nickel phosphate formation on soil from the former mining site under laboratory conditions will be discussed.

From the original research, a new concept for microbially aided, extracellular biomineral formation is developed. The concept thus extends the previous distinction of biomineralization on the part of the 'microbially induced' formation in a process oriented way, including microbial physiology and secondary metabolism into a unified concept of biomineralization.