关键词: 短乳杆菌, 胸苷磷酸化酶, 响应面法, 发酵培养基

Abstract: Thymidine phosphorylase plays a critical role in synthesis of nucleosides. In this study，fermentation medium of Lactobacillus brevis for producing thymidine phosphorylase was optimized. Firstly，three factors of fermentation time (P=0.032)，inoculum size (P=0.037) and glucose concentrations (P=0.022) significantly affected thymidine phosphorylase were identified by Plackett-Burman experiment. Then，the three factors were further optimized through steepest ascent path approaching the maximum response region and response surface central composite design (CCD). The optimal fermentation medium were as follows ：initial pH 8.0，glucose 18 g/L，yeast extract 15 g/L，NaCl 7.5 g/L，peptone 10 g/L，thymidine 15mmol/L. Culture conditions were as follows ：rotating speed 110r/min，temperature 38 ℃，fermentation time 10.57 h，inoculum size 1.54%. Under optimum conditions，the capacity of Lactobacillus brevis to produce thymidine phosphorylase was greatly improved，thymidine phosphorylase activity reached 1.172 U/mg wet bacteria which was increased by 2.93 times more than that before optimization. Protein gel electrophoresis showed that thymidine phosphorylase content per gram wet bacteria with optimized fermentation medium was obviously higher than that before optimization.

Key words: Lactobacillus brevis, thymidine phosphorylase, response surface methodology, fermentation medium