A method of recovering metal from low-grade minerals, factory effluent, plants and the like by using microorganisms has been known. For example, Patent Literature 1 (Japanese Patent Laid-Open No. 2011-52315) discloses a method of recovering metal in which a yeast adsorbing specific metal ions is caused to adsorb the specific metal and then, the metal is recovered by using a chelating agent. Patent Literature 2 (Japanese Patent Laid-Open No. 11-77008) discloses a method of recovering metal after immersing fishery wastes in an aqueous solution containing lactic acid, a yeast and hydrocarbon and then, subjecting it to fermentation treatment. Patent Literature 3 (Japanese Patent Laid-Open No. 2004-33837) discloses a method of recovering metal in which a plant containing heavy metal is immersed in a culture solution containing lactic acid, a yeast and sugar so as to dissociate the heavy metal and then, the heavy metal is recovered by using the chelating agent. Moreover, Patent Literature 4 (Japanese Patent Laid-Open No. 2003-284556) and Patent Literature 5 (National Publication of International Patent Application No. 2009-538127) disclose a method of recovering metal by using a transformant such as a yeast in which a gene which codes a protein capturing or adsorbing the metal is transformed. The protein indicated in Patent Literature 4 is histidine polypeptide, and Patent Literature 4 indicates that it is recovered as metal ions. The protein indicated in Patent Literature 5 is phytochelatin synthetase or metallothionein, and it is indicated that the protein is recovered as a complex of metal and a protein.
However, since metal is recovered as metal ions in these methods, these methods require an operation of reducing the recovered metal ions and moreover, an operation of separating the metal ions from the complex with the protein in order to recover metal.
On the other hand, Patent Literature 6 (Japanese Patent Laid-Open No. 2007-113116) describes a method of recovering metal from metal oxides or metal hydroxides by causing iron-reducing bacteria to act. In this method, metal (reduced form) in a fungus body of the iron-reducing bacteria can be recovered.
However, since this method utilizes an iron reducing action of the iron-reducing bacteria, an electron donor is essential in a culture medium. There was also a problem that, since the fungus body of the iron-reducing bacteria is small, recovery of the bacteria from the solution is difficult.
Moreover, other than the iron-reducing bacteria, Non-Patent Literature 1 describes that a metabolite secreted by Delftia acidovorans isolated from the natural world to an outside of a cell reduces/deposits a trivalent Au ion in the culture solution to an Au nanoparticle, but reduction of noble metal ions by yeast and accumulation as metal in the fungus body has not been known so far.
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USPTO Backgrounds