Isolation And Identification Of C-ring Cleavage Bacterium And The Activity Study Of The Metabolite

Soybean isoflavones (SI) are the secondary metabolites mainly composed by isoflavone daidzein and genistein. SI are degraded into equol and O-desmethylangolensin by intestinal microflora after being absorbed by microorganisms in gastra intestinal tract. Studies have shown that approximately 80%~90% of individuals in the populations studied are capable of producing O-Dma from daidzein. Previously, O-Dma was thought to be of weak biological activity by most people. In several subsequent studies, O-Dma has been shown to bind to human estrogen receptorsαandβ(ERαand ERβ) with a greater affinity than that of daidzein. After binding to ERβ, the contribution of O-Dma to induce gene transcription is higher than daidzein. Moreover, when the concentration was over 10μmol/L, O-Dma can evidently inhibit the growth of the cancer cell MCF-7.Strain AUH-HM195, which was isolated from crossoptilon mantchuricum feces, is the first reported facultative bacterium with highly daidzein cleavaging activity. The colony is regularly round, and the bacterium is globular orellipse under light microscope. According to the results of sugar fermentation and catalase, indole tests, the strain is initially presumed the genus of Enterococcus. Blast search revealed that its complete 16S rDNA gene sequence has 100% similarity to Enterococcus hirae(DSM20160). Based on chemical characteristies as well as analysis of the16S rDNA sequence, the strain AUH-HM195 was identified as Enterococcus hirae AUH-HM195.HPLC was used to detect the metabolite of isoflavones daidzein after being incubated with daidzein in BHI liquid medium under anaerobic conditions. In HPLC elution profiles, two peaks were observed. Peak one was determined as the metabolite of daidzein, since the peak area of which was increased when substrate daidzein was metabolized. However, the second peak did not show this rule and was determined as an unkown peak. Based on HPLC retention time, UV spectrum, 1H and 13C NMR analyses, the metabolite of daidzein by strain Enterococcus hirae AUH-HM195 was identified as O-desmethylangolensin. The preliminary antioxidant showed that O-DMA has the ability of scavenging both hydroxyl radical and superoxide anion. The unknown peak was ambiguously identified as naphthoquinone, which showed obviously bacterial inhibition ability to Escherichia coli, Staphylococcus aureus, Bacillus subtilis.