Summary: The first known report of the isolation of thermophilic bacteria which produce nitrile-degrading enzymes is presented. One of the strains isolated was studied in detail. Strain Dac521, classified as was capable of growth on acetonitrile, benzonitrile, propionitrile, acetamide, benzamide and propionamide as the sole carbon and nitrogen source in minimal nutrient media. The strain produced separate aliphatic-nitrile (e.g. acetonitrile)- and aromatic-nitrile (e.g. benzonitrile)-degrading activities. Acetonitrile-degrading activity was produced constitutively and enzyme production was not enhanced by the addition of substrate. Under conditions where benzonitrile was the sole carbon and nitrogen source in minimal nutrient media, acetonitrile-degrading enzyme activity was completely inhibited and benzonitrile-degrading activity was induced. Growth on substrates as sole carbon and nitrogen sources, together with the substrate specificity of cell-free extracts, suggested that acetonitrile and benzonitrile degradation may have occurred via nitrile hydratase and nitrilase pathways, respectively. Both the acetonitrile- and benzonitrile-degrading enzyme systems were significantly more thermostable in whole-cell preparations and cell-free extracts compared to their mesophilic counterparts.


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