Biodegradation of metal cyanides by mixed and pure cultures of fungi

Abstract

Former gasworks sites are sometimes be heavily contaminated with spent oxide which contains cyanide complexed to metals (especially iron). In this study, mixed fungal cultures have been isolated from acidic gasworks soil by their ability to utilize iron or nickel cyanide as the sole source of nitrogen at acidic or neutral pH, respectively. A mixed culture comprising Fusarium solani and Trichoderma polysporum was obtained by enrichment on tetracyanonickelate [K 2Ni(CN) 4] at pH 4. A second mixed culture consisting of Fusarium oxysporum, Scytalidium thermophilum, and Penicillium miczynski was isolated on hexacyanoferrate [K 4Fe(CN) 6] also at pH 4. Both consortia were able to grow on K 4Fe(CN) 6 as the sole source of nitrogen under acidic conditions. Growth was associated with progressive removal of cyanide from the culture supernatant. After the termination of growth, at least 50% of the total cyanide had been degraded. Growth of the fungi on K 2Ni( 14CN) 4 as a source of nitrogen at pH 7 yielded 14C-labelled carbon dioxide. Growth of the Fusarium isolates on K 2Ni(CN) 4 at pH 7, associated with the removal of cyanide, required 5 days as compared to 28 days on K 4Fe(CN) 6 at pH 4. Cyanide uptake by the fungi on K 4Fe(CN) 6 at pH 4 occurred simultaneously with removal of iron from the biomass-free medium. Pure cultures of F. solani and F. oxysporum were grown on K 2Ni(CN) 4 or K 4Fe(CN) 6 in pure culture at pH 7 or 4, respectively.