中文摘要：

菌株Aeroto-Niu-O16是经耐氧驯化后能在有氧条件下将大豆异黄酮黄豆苷元和染料木素分别加氢还原为二氢黄豆苷元和二氢染料木素的耐氧细菌菌株。通过本研究发现,该菌株在有空气氧条件下能将中药甘草主要活性成分甘草素（liquiritigenin）进行开环转化。中药甘草的乙醇粗提物直接酸水解即得底物甘草素。根据产物的最大紫外吸收图谱、质谱以及核磁共振氢谱和碳谱等测定结果,将菌株转化甘草素所生成的产物鉴定为达维荚蒾苷元（davidigenin）。菌株Aeroto-Niu-O16对底物甘草素的最大转化浓度为0.8 mmol.L1,平均转化率为71.7%;当向培养基中添加0.1%（m/v）的L-半胱氨酸或硫代硫酸钠时,底物甘草素的平均转化率可由原来的71.7%分别提高到78.3%和77.2%。检测浓度在0.2 mmol.L1到1.6 mmol.L1范围内,相同浓度下的产物达维荚蒾苷元对二苯代苦味酰基自由基（DPPH）的体外清除能力均显著或极显著高于底物甘草素。利用微生物生物转化法将甘草素转化为具有更高更广生理活性的达维荚蒾苷元尚属国内外首次报道。

英文摘要：

Aeroto-Niu-O16,an oxygen-tolerant bovine rumen bacterium,is capable of aerobically reducing isoflavones daidzein and genistein to dihydrodaidzein and dihydrogenistein through catalytic hydrogenation.In this study,it was found that bacterium strain Aeroto-Niu-O16 was able to cleavage the C-ring of liquiritigenin（LG）,which is one of the main biologically active components of licorice roots,in the presence of atmospheric oxygen.LG was prepared by acid hydrolysis of the crude extract of licorice roots.The metabolite of LG obtained in strain Aeroto-Niu-O16 was identified as davidigenin（DG） based on the data of UV,MS,1H and 13C NMR.The maximal concentration of LG that the strain Aeroto-Niu-O16 was able to transform effectively was 0.8 mmol-L-1 and the average productivity of the metabolite DG was 71.7%.Furthermore,when 0.1%（m/v） of L-cysteine or sodium thiosulfate was added in the cultural medium,the average bioconversion rate of LG was increased from 71.7% to 78.3% and 77.2%,respectively.The in vitro antioxidant investigation showed that 1,1-diphenyl-2-picrylhydrazyl（DPPH） radical-scavenging activity of DG was significantly or extremely significantly higher than that of LG at the concentrations from 0.2 mmol-L-1 to 1.6 mmol-L-1.We discoverd for the first time that LG can be converted to DG,which has stronger and wider biological activities,through microbial biotransformation method.