Gondwanaland, Formation
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GONDWANALAND, FORMATION
10 µm
Gold, Figure 2 Laser scanning micrograph (ex. 488 nm, em. 543 nm) of microorganisms (green) on a gold grain (red) from the Eder River, Germany. Eubacteria labeled by oligonucleotide probe EuB-CY3.
and not in the surrounding sediments. With a similarity of 99%, the sequence correlated to Cupriavidus (Ralstonia) metallidurans. Ninety percent of the bacteria in the laboratory experiment died because of the toxicity of AuCl 4. The surviving cells adapted themselves to the high concentration of Au(III) ions and precipitated gold. In addition to morphological studies (Bischoff, 1997), this provides evidence for bioaccumulation of secondary gold (e.g., nuggets, gold grains) by bacteria like C. metallidurans (Figure 2). The basal biochemical microbial processes of the biomineralization of gold are not completely understood yet. Precipitation of gold provides the cellular defense of C.metallidurans and is controlled by a coupling of efflux, reduction and possibly methylation of gold complexes (Reith et al., 2009). Reith et al. (2007) have published a comprehensive review of the geomicrobiology of gold.
Summary Different microorganisms are partially resistant to dissolved gold. Various microbial activities precipitate gold. Biofilms of Cupriavidus metallidurans accumulate gold naturally and contribute to the formation of secondary gold. Bibliography Benedetti, M., and Boulègue, J., 1991. Mechanism of gold transfer and deposition in a supergene environment. Geochimica et Cosmochimica Acta, 55, 1539–1547.
Bischoff, G. C. O., 1997. The biological origin of bacterioform gold from Australia. Neues Jahrbuch Geologische Paläontologische Abhandlungen, H6, 329–338. Karthikeyan, S., and Beveridge, T. J., 2002. Pseudomonas aeruginosa biofilms react with and precipitate toxic soluble gold. Environmental Microbiology, 4(11), 667–675. Kashefi, K., Tor, J. M., Nevin, K. P., and Lovley, D. R., 2001. Reductive precipitation of gold by dissimilatory Fe(III)-reducing bacteria and archaea. Applied and Environmental Microbiology, 67(7), 3275–3279. Lengke, M. F., and Southam, G., 2005. The effect of thiosulfateoxidizing bacteria on the stability of the gold–thiosulfate complex. Geochimica et Cosmochimica Acta, 69(15), 3759–3772. Lengke, M. F., Ravel, B., Fleet, M. E., Wanger, G., and Southam, G., 2006. Mechanisms of gold bioaccumulation by filamentous cyanobacteria from gold(III)–chloride complex. Environmental Science & Technology, 40(20): 6304–6309. Nakajima, A., 2003. Accumulation of gold by microorganisms. World Journal of Microbiology, 19, 369–374. Nordstrom, D. K., and Southam G., 1997. Geomicrobiology of sulfide mineral oxidation. Reviews in Mineralogy and Geochemistry, 35, 361–390. Reith, F., Rogers, S., McPhail, D. C., and Webb, D., 2006. Biomineralization of gold: biofilms on bacterioform gold. Science, 313, 333–336. Reith, F., Lengke, M. F., Falconer, D., Craw, D., and Southam, G., 2007. The geomicrobiology of gold. ISME Journal, 1, 567–584. Reith, F., Etschmann, B., Grosse, C., Moors, H., Benotmane,
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