CYANIDE DEGRADATION UNDER ALKALINE CONDITIONS BY A STRAIN OF FUSARIUM-SOLANI ISOLATED FROM CONTAMINATED SOILS

Several cyanide-tolerant microorganisms have been selected from alkali ne wastes and soils contaminated with cyanide, Among them, a fungus id entified as Fusarium solani IHEM 8026 shows a good potential for cyani de biodegradation under alkaline conditions (pH 9.2 to 10.7), Results of (KCN)-C-14 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-hydrolyz ing enzyme, cyanide hydratase (EC 4.2.1.66); and (ii) the second react ion consists of the conversion of formamide to formate, which is assoc iated viith 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 prese nce of organic nutrients in the medium has a major influence on the oc currence of the second step. Addition of small amounts of yeast extrac t led to fungal growth, whereas no growth was observed in media contai ning cyanide as the sole source of carbon and nitrogen, The simple hyd rolytic detoxification pathway identified in the present study could b e used for the treatment of many industrial alkaline effluents and was tes containing free cyanide without a prior acidification step, thus l imiting the risk of cyanhydric acid volatilization; this should be of great interest from an environmental and health point of view.