Medium Optimization for Nitrilase Production by Newly Isolated Rhodococcus erythropolis ZJB-0910 Using Statistical Designs

H. Dong, Z. Liu, Y. Zheng and Y. Shen

Abstract
The objective of this work is to investigate the effects of the medium components including carbon sources, nitrogen sources and metal ions on nitrilase production from R. erythropolis ZJB-0910, which was applied in stereoselective hydrolysis of racemic ethyl 4-cyano-3-hydroxybutyate to (R)-ethyl-3-hydroxyglutarate [(R)-EHG]. In this study, glucose, yeast extract and MgSO4 were selected as the suitable components, and the concentrations of these three factors for the zero coded levels of variables in the subsequent optimization were confirmed through the empirical ‘one-factor-at-a-time’ experiments. The combination of response surface methodology (RSM) and Box-Behnken factorial design was carried out to establish a quadratic model to fit the nitrilase activity and the variables. The maximum nitrilase activity of 77.482 U g–1 was predicted when glucose concentration was 20.986 g L–1, yeast extract concentration was 8.468 g L–1, and MgSO4 concentration was 0.22 g L–1. Validation experiments were carried out under the optimized conditions for verification of the model, and the nitrilase activity was found to be improved by 1.77 fold, compared to the value before optimization. The strain growth curve and nitrilase activity alteration in the course of culture were also examined, and the cells were suitably harvested after being cultured for 45~48 h.

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Keywords
Nitrilase, stereoselective hydrolysis, (R)-ethyl-3-hydroxyglutarate, optimisation, response surface methodology, Box-Behnken