Isolation, identification and biotransforming property of an isoflavone reducing bacterium isolated from rabbit intestinal microflora

Abstract:

[Objective] To isolate specific bacteria capable of biotransforming isoflavones daidzein and genistein from fresh feces of rabbit. [Methods] In an anaerobic chamber, fresh fecal samples of rabbit were diluted before being spread on agar plate. Single colonies were picked randomly and incubated with daidzein or genistein. High performance liquid chromatography (HPLC) was used to detect whether the isolated bacteria were able to biotransform the substrate daidzein or genistein. [Results] A Gram-positive obligate anaerobic bacterium, which we named AUH-JLR41 (KJ188150), capable of biotransforming isoflavones daidzein and genistein was isolated. Based on the HPLC retention time, UV spectra and electrospray ionization mass spectrometry (ESI-MS) analysis, the metabolites of daidzein and genistein were identified as dihydrodaidzein (DHD) and dihydrogenistein (DHG), respectively. Chiral stationary-phase HPLC successfully separated the two peaks which had the same peak area, indicating that the enantiomeric excess of biosynthesized DHD and DHG was zero. Biotransformation kinetics showed that daidzein was reduced to DHD completely after 48 h incubation and genistein was reduced to DHG after 72 h incubation under anaerobic conditions. Moreover, the maximal concentrations of daidzein and genistein that strain AUH-JLR41 was able to convert were 0.6 mmol/L. BLAST search on the GenBank revealed that the 16S rRNA gene sequence for strain AUH-JLR41 had the highest similarity to that of Slackia equolifaciens DZE (EU377663), the similarity of which was 99.6%. [Conclusion] Bacterium strain AUH-JLR41 isolated from rabbit feces was able to reduce isoflavones daidzein and genistein to DHD and DHG, respectively, under anaerobic conditions.