Microbial hydrolysis of organic nitriles and amides

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

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(sup14)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.

Isolation and properties of a nitrile hydratase from the soil fungus Myrothecium verrucaria that is highly specific for the fertilizer cyanamide and cloning of its gene

A protein was purified from crude extracts of the soil fungus Myrothecium verrucaria by gel filtration and hydrophobic chromatography to homogeneity; this protein catalyzed the stoichiometric hydration of the fertilizer cyanamide to urea with high substrate specificity. This cyanamide hydratase (urea hydro-lyase; EC 4.2.1.69) contained zinc and consisted of six identical subunits with Mr = 27,700. It was partially sequenced. The protein was detectable only when the fungus was grown on cyanamide as the sole nitrogen source. Genomic DNA from the fungus was cloned, and the gene encoding the enzyme was mapped with an oligonucleotide probe derived from the amino acid sequence within a 25,800-base-pair DNA region. The subunit of the enzyme is encoded by a 795-base-pair DNA sequence containing a 63-base-pair intron. A cDNA clone containing the intronless gene with an open reading frame encoding a sequence of 244 amino acids expressed the enzyme in active form in Escherichia coli with excellent yield.