Isolation, Biotransforming Property And Oxygen-tolerant Domestication Of An Arctigenin Biotransforming Bacterium

Burdock is the ripe and dry seed of Asteraceae herb Arctium lappa L., which are of many pharmacological effects, including anti-inflammatory, anti-cancer, anti-HIV, and anti-diabetic, etc. Plant lignans arctiin and arctigenin are the main components of the traditional Chinese herb Arctium lappa L. Arctigenin was obtained by acid hydrolysis of the crude extract of Arctium lappa L. Arctigenin can be converted by rat or human intestinal micro flora to a series of metabolites.In this study, we isolated a new Gram-positive obligate anaerobic bacterium, which we named strain AUH-JLD56from fresh human feces, the bacterium of which was able to bioconvert arctigenin to3’-desmethylarctigenin (3’-DMAG) soly and efficiently. Basic Local Alignment Search Tool (BLAST) search on the GenBank revealed that the full-length of16S rDNA sequence for strain AUH-JLD56has99.2%similarity to that of Blautia wexlerae strain WAL145079(EF036467). Its16s rDNA sequence was sended to NCBI gene bank, the Accession Number we got is KF374935. Therefore, bacterium strain AUH-JLD56was named as Blautia sp. AUH-JLD56. It was the first report of the world that strain AUH-JLD56can bioconvert arctigenin to3’-DMAG solely and efficiency.The biotransforming kinetics of arctigenin by strain AUH-JLD56was investigated. The results showed that90.5%of the substrate arctigenin was converted when the substrate was incubated with the bacterium for12h, and96.3%of the substrate was converted when the incubation time was16h. However, the amount of the product did not increase anymore when the incubation time was extended to24h. Study on biotransforming capacity showed that strain AUH-JLD56was able to convert all the substrate arctigenin to3’-DMAG when the concentration of arctigenin was lower than0.6mmol/L. The average biotransformation rate of the substrate arctigenin was97.4%,96.5%and90.5%when the concentration of arctigenin was1.2mmol/L,2.4mmol/L and3.6mmol/L, respectively. However, the average biotransformation rate of the substrate arctigenin was only54.4%when the concentration of the arctigenin was increased to4.0mmol/L. Therefore, the maximal concentration of the substrate arctigenin that strain AUH-JLD56could biotransform efficiently was3.6mmol/L.The in vitro antioxidant investigation showed that1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity of3’-DMAG was significantly higher than that of the substrate arctigenin at concentrations ranging from 0.025mmol/L to0.1mmol/L (p<0.01). In addition, we found that under the same concentration, the DPPH scavenging rate of arctigenin was significantly higher than that of equol and enterolactone, which have been reported to be of strong antioxidant activity and strong estrogen activity(p<0.01). We here show for the first time that under the same concentration, the DPPH scavenging rate of the product3’-DMAG is significantly higher than that of the substrate arctigenin, equol and enterolactone, respectively.After a long-term oxygen-tolerant domestication process, an oxygen-tolerant mutant strain, which we named Aeroto-AUH-JLD56was obtained. The mutant strain Aeroto-AUH-JLD56differed from the original strain AUH-JLD56in bacterial shape (from elliptical to middle-to-long rods) and some biochemical traits (from urease negative to positive; the capability to use most carbohydrates). The maximal concentration of the substrate arctigenin that strain Aeroto-AUH-JLD56was able to biotransform efficiently in the presence of atmospheric oxygen was2.8mmol/L and the average biotransformation rate was89.2%.