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Genome mining of cyanide-degrading nitrilases from filamentous fungi


A variety of fungal species are known to degrade cyanide through the action of cyanide hydratases, a specialized subset of nitrilases which hydrolyze cyanide to formamide. In this paper, we report on two previously unknown and uncharacterized cyanide hydratases from Neurospora crassa and Aspergillus nidulans. Recombinant forms of four cyanide hydratases from N. crassa, A. nidulans, Gibberella zeae, and Gloeocercospora sorghi were prepared after their genes were cloned with N-terminal hexahistidine purification tags, expressed in Escherichia coli, and purified using immobilized metal affinity chromatography. These enzymes were compared according to their relative specific activity, pH activity profiles, thermal stability, and ability to remediate cyanide contaminated waste water from silver and copper electroplating baths. Although all four were similar, the N. crassa cyanide hydratase (CHT) has the greatest thermal stability and widest pH range of >50% activity. N. crassa also demonstrated the highest rate of cyanide degradation in the presence of both heavy metals. The CHT of A. nidulans has the highest reaction rate of the four fungal nitrilases evaluated in this work. These data will help determine optimization procedures for the possible use of these enzymes in the bioremediation of cyanide-containing waste. Similar to known plant pathogenic fungi, both N. crassa and A. nidulans were induced to express CHT by growth in the presence of KCN.

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The financial support of the Robert A. Welch Society (Grants E-1263 and A-1310) and the Texas Hazardous Substance Research Center are gratefully acknowledged. The Fungal Genetic Stock Center created the locus disruptions promptly upon our request, and Dr. Wayne Versaw was instrumental in assisting us with the growth and characterization of the fungal strains.

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Correspondence to Michael J. Benedik.

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Basile, L.J., Willson, R.C., Sewell, B.T. et al. Genome mining of cyanide-degrading nitrilases from filamentous fungi. Appl Microbiol Biotechnol 80, 427 (2008).

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  • Cyanide
  • Cyanide hydratase
  • Bioremediation