Gold and Silver Trapping by Uncultured Magnetotactic Cocci

• Published in: Geomicrobiology journal 2005-01, Vol.22 (1-2), p.55-63
• Main Authors: Keim, Carolina N., Farina, Marcos
• Format: Article
• Language: English
• Subjects: biomineralization; gold; heavy metals; magnetotactic bacteria; polyphosphate granules; silver; X-ray microanalysis
• ISSN: 0149-0451; 1521-0529
• DOI: 10.1080/01490450590922550

We studied the sites of gold and silver trapping by uncultured magnetotactic cocci from microcosms using transmission electron microscopy and energy-dispersive X-ray analysis. Two morphotypes were found to trap gold or silver. Morphotype 1 had large magnetite crystals frequently twinned in an unusual way and contained phosphorus-rich granules and electron-lucent inclusions probably composed of polyhydroxyalkanoates. Morphotype 2 presented smaller crystals with smaller width/length ratios and granules containing C, O, P, S, Cl, Na, Mg, Ca, and Fe, called phosphorus-sulfur-iron granules due to the presence of relatively large amounts of phosphorus, sulfur and iron. Gold was found in morphotype 2 bacteria, mainly in phosphorus-sulfur-iron granules. Additionally, the capsule presented small deposits that seemed to be composed of elemental gold. Silver was found in both spherical and rosette-shaped crystalline deposits also containing sulfur at the cell envelope of morphotype 1 bacteria. The rosette-shaped deposits had six subunits, suggesting that a homohexameric macromolecular assembly might be involved in their nucleation process. This seems to be an example of a highly organized structure mineralized incidentally by a biologically induced biomineralization process.