[C-ring cleavage of isoflavone daidzein by a newly-isolated facultative Enterococcus hirae AUH-HM195 from Crossoptilon mantchuricum feces].

Objective To isolate specific bacteria capable of biotransforming isoflavone daidzein. Methods Fresh crossoptilon mantchuricum feces was diluted serially from 10(-1) to 10(-8) in Brain Heart Infusion (BHI) liquid medium in the anaerobic chamber at 37 degrees C. Single colony was isolated and incubated in BHI liquid medium containing 0.1 mmol/L daidzein under anaerobic conditions. The culture medium was detected by HPLC method after being incubated for 3 days. Results A gram-positive facultative anaerobic bacterium designated strain AUH-HM195 capable of cleaving the C-ring of isoflavone daidzein was isolated. Basic Local Alignment Search Tool (BLAST) search on the GenBank revealed that the full-length of 16S rDNA gene sequence for strain AUH-HM195 has 100% similarity to that of Enterococcus hirae (DSM20160). Based on HPLC retention time, UV spectrum, 1H and 13C NMR analysis,the metabolite of daidzein by strain Enterococcus hirae AUH-HM195 was identified as O-desmethylangolensin. Two peaks were observed when purified O-desmethylangolensin was eluted on a chiral column. The enantiomeric excess (% e.e.) of O-desmethylangolensin was 66.9%. Conclusion Bacterial strain Enterococcus hirae AUH-HM195 is the first reported Enterococcus bacterium with C-ring cleavage activity. It is also the first reported facultative bacterium capable of metabolizing isoflavones.