Medium Optimization for Enzymatic Production of L-Cysteine by Pseudomonas sp. Zjwp-14 Using Response Surface Methodology 

Guo-Ying Lv^1,2, Pu Wang¹*, Jun-Yao He¹ and Xiao-Nian Li<sup>3

1</sup>Institute of Biopharmaceutical Engineering, Zhejiang University of Technology, CN-310014 Hangzhou, PR China
²Zhejiang Academy of Agricultural Sciences, CN-310021 Hangzhou, PR China
³College of Chemical Engineering and Materials Science, Zhejiang University of Technology, CN-310014 Hangzhou, PR China

Article history:
Received September 7, 2007
Accepted June 18, 2008

Key words:
DL-2-amino-Δ²-thiazoline-4-carboxylic acid (DL-ATC), L-cysteine, medium optimization, Pseudomonas sp. Zjwp-14, response surface methodology

Summary:
Response surface methodology was applied to optimize medium constituents for enzymatic production of L-cysteine from DL-2-amino-Δ²-thiazoline-4-carboxylic acid (DL-ATC) by a novel Pseudomonas sp. Zjwp-14. With the Plackett-Burman design experiment, glycerol, DL-ATC, yeast extract, and pH were found to be the most powerful factors among the eight tested variables that influence intracellular enzyme activity for biotransformation of DL-ATC to L-cysteine. In order to investigate the quantitative effects for four variables selected from Plackett-Burman design on enzyme activity, a central composite design was subsequently employed for further optimization. The determination coefficient (R²) was 0.9817, and the results show that the regression models adequately explain the data variation and represent the actual relationships between the parameters and responses. The optimal medium for Pseudomonas sp. Zjwp-14 was composed of (in g/L): glycerol 16.94, DL-ATC 4.59, yeast extract 6.99, NaCl 5.0, peptone 5.0, beef extract 5.0, MgSO₄·7H₂O 0.4, and pH=7.94. Under the optimal conditions, the maximum intracellular enzyme activity of 918.7 U/mL in theory and 903.6 U/mL in the experiment were obtained, with an increase of 15.6 % compared to the original medium components. In a 5-litre fermentor, cultivation time for Pseudomonas sp. Zjwp-14 was cut down for 6 h and the maximum enzyme activity reached 929.6 U/mL.

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