Biosorption of gold occurs in a variety of organisms representing gram-positive and gram-negative bacteria, archaea, fungi, and algae. Biological removal of Au(III) from solution is often accompanied by reduction of Au(III) to elemental gold (Au(0)). Some Fe(III)-reducing bacteria and archaea can reduce Au(III) to Au(0) using hydrogen gas as an electron donor. This reductive mechanism is thought to be enzymatically mediated and to be separate from Fe(III) reduction, as not all Fe(III)-reducing organisms can also reduce Au(III) (Kashefi et al., 2001).

Isolated cell walls from Bacillus subtilis collect granules of elemental gold when treated with a solution of AuCl₃ (Beveridge and Murray, 1976). While the accumulation of elemental gold most often occurs on the surface of the organism, a study of the effects of different types of lipopolysaccharide O-side chains on metal binding in Pseudomonas aeruginosa found precipitated gold distributed randomly throughout the cytoplasm and not accumulated at the cell surface (Langley and Beveridge, 1999).

Reductive precipitation is not always required for microbial gold accumulation. Bacillus cereus cells were shown to bind gold particles from a suspension of colloidal gold in what may be an ATP-dependent process (Ulberg et al., 1992).

A biological role for gold has been reported in Micrococcus luteus. An NADH oxidase in M. luteus containing three Au(III) ions per active site was found to catalyze oxidation of methane to methanol (Levchenko et al., 2002).

For more information:

Search Medline for gold metabolism AND bacteria

Savvaidis I. Recovery of gold from thiourea solutions using microorganisms. Biometals. 1998 Apr;11(2):145-51.

Pethkar AV, Kulkarni SK, Paknikar KM. Comparative studies on metal biosorption by two strains of Cladosporium cladosporioides. Bioresour Technol. 2001 Dec;80(3):211-5.

Levchenko LA, Sadkov AP, Marakushev SA, Lariontseva NV. Participation of biological membranes in colloidal gold transformation by Micrococcus luteus cells. Membr Cell Biol. 1997;11(1):131-5.