Enantioselective biocatalytic hydrolysis of (R,S)-mandelonitrile for production of (R)-(-)-mandelic acid by a newly isolated mutant strain.

(R)-(-)-Mandelic acid (R-MA) is an important intermediate with broad uses. Recently, R-MA production using nitrilase has been gaining more and more attention due to its higher productivity and enantioselectivity. In this work, a new bacterium WT10, which exhibited favorable nitrilase activity and excellent enantioselectivity for production of R-MA by enantioselective biocatalytic hydrolysis of (R,S)-mandelonitrile, was isolated and identified as a strain of Alcaligenes faecalis. In order to improve its nitrilase activity for industrial application, the wild-type strain WT10 was further subjected to mutagenesis using a combined LiCl-ultraviolet irradiation and low energy N(+) ion beams implantation technique. A valuable mutant strain A. faecalis ZJUTB10 was obtained. The nitrilase specific activity of the mutant strain was greatly improved up to 350.8 U g(-1), in comparison with wild-type strain WT10 of 53.09 U g(-1). The reaction conditions for R-MA production by mutant strain A. faecalis ZJUTB10 were also optimized. Nitrilase activity in mutant strain showed a broad pH optimum at pH 7.7-8.5. The optimal temperature was 35°C. The highest production rate reached 9.3 mmol h(-1) g(-1). The results showed that mutant strain A. faecalis ZJUTB10 was a new candidate for efficient R-MA production from (R,S)-mandelonitrile and could potentially be used in industrial production.