Abstract
A new bacterial isolate Klebsiella oxytoca 38.1.2 with stereoselective nitrile hydratase activity against rac-2-phenylglycine nitrile, rac-2-phenylpropionitrile and rac-mandelonitrile was investigated. The cultivation conditions for growth and nitrile hydratase formation were studied. An intracellular ( S)-enantioselective nitrile hydratase and a putative ( S)-selective amidase were found to be induced in the presence of rac-2-phenylpropionitrile. The temperature dependence on the enantioselectivity of the nitrile hydratase active cells was studied in more detail for the biotransformation of rac-2-phenylpropionitrile and rac-mandelonitrile. By increasing the temperature from 15 °C to 37 °C, the apparent enantiomeric ratio of the conversion of rac-2-phenylpropionitrile to ( S)-2-phenylpropionamide increased from 16 to 35 at nearly 50% conversion rate. rac-Mandelonitrile was converted to ( S)-mandelamide with an enantiomeric excess of up to 95% in a 80% yield without further conversion to mandelic acid.
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