Cyanide Degradation under Alkaline Conditions by a Strain of Fusarium solani Isolated from Contaminated Soils

Abstract

Several cyanide-tolerant microorganisms have been selected from alkaline wastes and soils contaminated with cyanide. Among them, a fungus identified as Fusarium solani IHEM 8026 shows a good potential for cyanide biodegradation under alkaline conditions (pH 9.2 to 10.7). Results of K 14 CN biodegradation studies show that fungal metabolism seems to proceed by a two-step hydrolytic mechanism: (i) the first reaction involves the conversion of cyanide to formamide by a cyanide-hydrolyzing enzyme, cyanide hydratase (EC 4.2.1.66); and (ii) the second reaction consists of the conversion of formamide to formate, which is associated with fungal growth. No growth occurred during the first step of cyanide degradation, suggesting that cyanide is toxic to some degree even in cyanide-degrading microorganisms, such as F. solani. The presence of organic nutrients in the medium has a major influence on the occurrence of the second step. Addition of small amounts of yeast extract led to fungal growth, whereas no growth was observed in media containing cyanide as the sole source of carbon and nitrogen. The simple hydrolytic detoxification pathway identified in the present study could be used for the treatment of many industrial alkaline effluents and wastes containing free cyanide without a prior acidification step, thus limiting the risk of cyanhydric acid volatilization; this should be of great interest from an environmental and health point of view.

Degradation of tetracyanonickelate (II) by Cryptococcus humicolus MCN2

“…Some species including Stemphylium loti [14], Fusarium lateritium [7], and Gloeocerocospora sorghi [8,17] only detoxify cyanide to formamide by the action of cyanide hydratase and none of these fungi utilizes cyanide as a source of carbon or nitrogen. In contrast, some species such as F. oxysporum, Gliocladium virens, Trichoderma koningii [18], and F. solani IHEM 8026 [9] could grow on KCN as a sole nitrogen source. It is not known whether they can degrade metal^cyano complexes.…”

“…Some fungi detoxify cyanide by cyanide hydratase producing formam-ide that is not further degraded and not used as a nitrogen source [7,8]. However, it has recently been shown that fungi also utilize cyanide as a source of nitrogen, including Fusarium solani IHEM 8026 on free cyanide [9], F. solani on K 4 Fe(CN) 6 and K 2 Ni(CN) 4 [10] and Fusarium oxysporum N-10 on K 2 Ni(CN) 4 [11].…”

Cyanide degradation and antagonistic potential of endophytic Bacillus subtilis strain BEB1 from Bougainvillea spectabilis Willd

“…Effluents from industries involved in metal plating, coal coking, coal gasification, ore leaching, aluminum electrolysis, manufacturing of pharmaceuticals, plastics and synthetic fibers contain large amounts of cyanides (Dumestre et al 1997). To minimize health and environmental risks, the cyanide content in these effluents has to be reduced to very low levels (0.1 mg of CN per liter) before discharging (Smith and Mudder 1991).…”

Cassava Wastewater and Solid Waste Leachate as Cyanogenic Substrates for the Growth of Nitrile and Linamarin-Utilizing Bacteria

“…In most of the recent studies, researchers carried out on cyanide removal using different bacteria under different conditions. Most of the bacteria were mesophilic while optimal temperature and pH ranged were about 25 -30°C and 5.5 to 11.5 respectively [30]. Ezzi and Lynch [33] studied cyanide removal at a concentration of 2,000 ppm and successfully removed total cyanide at 90 days.…”