中文摘要：

【目的】解析氮源浓度对米根霉木糖代谢途径及产物的影响，提高木糖利用率。【方法】以木糖为碳源，考察不同氮源浓度下米根霉的生物量、有机酸积累量、木糖代谢关键酶（木糖还原酶、葡萄糖．6．磷酸脱氢酶）活力以及胞内还原力（NADH／NAD＋、NADPH／NADP＋）的差异。【结果】富氮条件下（2．4g／L尿素），木糖代谢速率达2．03g／（L·h），木糖还原酶、葡萄糖-6-磷酸脱氢酶的活力以及胞内还原力较高，生物量达18．01g／L，几乎不积累有机酸；限氮条件下（0．15g／L尿素），木糖还原酶、葡萄糖．6．磷酸脱氢酶的活力以及胞内还原力水平降低，生物量仅4．02g／L，富马酸积累量为6．55g／L，残余木糖量较高；氮源浓度为0．6g／L时，木糖还原酶和葡萄糖-6-磷酸脱氢酶的活力以及NADPH／NADP＋处于前二者之间，此时生物量9．11g／L，有机酸积累量较大，其中富马酸为12．28g／L。【结论】充足的氮源可使米根霉通过木糖代谢关键酶与胞内还原力的协同效应强化木糖代谢活力，通过优化氮源浓度后，米根霉可积累更多有机酸。

英文摘要：

[ Objective] We studied the effects of nitrogen concentration on xylose metabolism and organic acid production in Rhizopus oryzae. [ Methods] We studied the effect of different nitrogen concentration in media on biomass, organic acids accumulation, activity of key enzymes （xylose reductase, XR, glucose-6-phosphate dehydrogenase, G6PD） involved in the metabolism and intracellular redox ratios of R. oryzae. [ Results ] Both intracellular redox ratios and key enzymes activities stayed low, resulting in 4.02 g/L biomass, 6.55 g/L fumaric acid production and high concentration of residual xylose under nitrogen-limitation conditions （0. 15 g/L urea）. Intracellular redox ratios and activity of key enzymes increased under rich nitrogen culture （2.4 g/L urea）, leading to high biomass 18.01 g/L, high xylose uptake speed 2.03g/（L.h） but low fumaric acid production （0.27 g/L）. When concentration of urea was 0.6 g〈/L, biomass 9. 11 g/L and fumaric acid 12.28 g/L, NADPH/NADP ＋ , XR and G6PD activities were medium whereas NADH/NAD ＋ reached the highest compared to those in rich nitrogen or nitrogen limitation. ~ Conclusionl Sufficient nitrogen source strengthened the xylose metabolic activity by promoting the key enzymes activity and intracellular redox ratios in R. oryzae. Optimized nitrogen concentration will enhance fumaric acid production with R. oryzae.