Full Length Research Paper

Enhanced production of intracellular dextran dextrinase from Gluconobacter oxydans using statistical experimental methods

Xiangzhao Mao^2#, Xiaotong Liang^1,2#, Shu Wang², Wei Dong^1,2, Yanlong Xing², Hualei Wang², Lizhong Guo¹* and Dongzhi Wei^2,3*

¹Shandong Province Key Lab of Applied Mycology, Qingdao Agricultural University, China.

²Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, China.

³State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, China.

*Corresponding author. E-mail: lzguo@qau.edu.cn and dzhwei@ecust.edu.cn. Tel: +86-532-88030375 and +86-21-64252078. Fax: +86-21-64250068.

Abbreviations: DDase, Dextran dextrinase; CCD, central composite design; DSase, dextran sucrase;  NPG, p-nitrophenyl-α-D-glucopyranoside; R², determination coefficient; RSM, response surface methodology.

#These authors contributed equally to this paper

Accepted 14 January, 2010

   Abstract

Optimization of the fermentation medium for DDase production by Gluconaobacter oxydans M5 was carried out in the shake flasks using two kinds of statistical methods. Four variables, namely glucose, tryptone, yeast extract and sodium chloride, were found to influence DDase production significantly by the Plackett-Burman screening. A four-factor five-level central composite design (CCD) was chosen to explain the combined effects of the four medium constituents. The optimum medium consisted of glucose (17.670 g/L), maltobiose (30 g/L), tryptone (12.198 g/L), yeast extract (13.528 g/L), ammonium nitrate (15 g/L), copper sulfate (0.01 g/L), zinc sulfate (0.01 g/L), and sodium chloride (0.009 g/L); the initial pH 6.0 was set prior to sterilization. The DDase yield obtained from optimized medium increased by 17-fold (0.238 U/mL) or so. Under these optimal conditions, the experimental values agreed with the predicted values, indicating that the chosen method of optimization of medium composition was efficient, relatively simple, time reducing and material saving.

Key words: Dextran dextrinase, Gluconobacter oxydans, medium optimization, Plackett-Burman design, central composite design.