Microbial Mineral Solubilization: the Formation of water-soluble Metal Cyanides by Cyanogenic Microorganisms

Microorganisms are able to solubilize metals from solids by redox processes, by the formation of organic and inorganic acids, and by metal complexation due to the formation of metabolic intermediates. Cyanide (CN-) or hydrocyanic acid (HCN) is formed by a variety of bacteria (e.g. Chromobacterium violaceum, Pseudomonas aeruginosa, Pseudomonas fluorescens) and fungi (e.g. Marasmius oreades, Clitocybe sp., Polysporus sp.). However, their ability to solubilize metals has not been investigated so far.

Main research questions address

• the cultivation and growth optimization of cyanogenic microorganisms
• the stimulation of cyanide formation
• the microbiological treatment of metal-containing solid waste materials and the recovery of metal cyanides

All microorganisms investigated were able to form water-soluble metal cyanides, however, with different efficiencies. Cyanide complexed nickel and copper was formed in the presence of nickel- and copper-containing minerals, respectively. The findings demonstrate for the first time the microbial mobilization of metals from solid materials and represent a novel type of microbial metal mobilization based on the ability of certain microbes to form HCN.

PD Dr. Helmut Brandl (Project Leader)

Prof. Dr. Walter Krebs, Zurich University of Applied Sciences, Wädenswil
Dr. Monika Maurhofer, Institute of Integrative Biology, ETH Zurich
Tehran University of Medical Sciences, Teheran, Iran

Rudolf von Rohr M., Furrer G., Brandl H. (2009) Effect of iron and phosphate on bacterial cyanide formation determined by methemoglobin in two-dimensional gradient microcultivations. Journal of Microbiological Methods 79: 71-95.

Brandl H. Lehmann S., Faramarzi M.A., Martinelli D. (2008) Biomobilization of silver, gold, and platinum from solid waste materials by HCN-forming microorganisms. Hydrometallurgy 94: 14-17.

Brandl H., Faramarzi M.A. (2006) Microbe-metal-interactions for the biotechnological treatment of metal-containing solid waste. China Particuology 4: 93-97.

Faramarzi, M.A., Brandl, H. (2006) Formation of water-soluble metal cyanide complexes from solid minerals by Pseudomonas plecoglossicida. FEMS Microbiology Letter 259: 47-52.

Faramarzi M.A., Stagars M., Pensini E., Krebs W., Brandl H. (2004) Metal solubilization from metal-containing solid materials by cyanogenic Chromobacterium violaceum. Journal of Biotechnology 113: 321-326.