ABSTRACT
Bacteria require highly reactive surfaces to ensure that they have good interaction with their immediate surroundings. They are exquisitely small, but have the highest surface area-to-volume ratio of any life form. These two factors, reactive surfaces and expansive shoulders, ensure that there is strong interplay with environmental metal ions so that the ions are electrostatically complexed with available cellular surface chemical groups at circumneutral pH, primarily carboxyl and phosphoryl groups. This complexation lowers the available free energy of each site, thereby promoting precipitation of additional metal ions together with available counterions. Over time, precipitates grow larger and (often) dehydrate, thereby developing bona fide crystalline mineral phases. We can only marvel at the consequences of this type of microbe geoprocessing, which presumably has been going on since the dawn of life about 3.6 billion years ago. Ehrlich's book, Geomicrobiology (1981), puts this process into perspective and more detailed accounts can be found in Douglas & Beveridge (1998), Fortin et al. (1998), Fein et al. (2001), and Korenevsky et al. (2002).
