A newly isolated bacterium, named as AUH-JLC257, was found to be capable of bioconverting isoflavone genistein to 5-hydroxy-equol under anaerobic conditions. The metabolite 5-hydroxy-equol was identified by using UV spectrum, electrospray ionization mass spectrometry （ESI-MS） as well as IH and 13C NMR analyses. Chiral stationary-phase high-performance liquid chromatography analysis and specific rotation examination demonstrated that the bio-synthesized 5-hydroxy-equol was just （-）-5-hydroxy-equol. The average bioconverting rate was 83.1%, and the strain AUH-JLC257 could efficiently transform genistein at a maximal substrate concentration of 0.6 mmol/L. We, for the first time, showed that the bio-synthesized 5-hydroxy-equol had 1,1-diphenyl-2-picrylhydrazyl （DPPH） radical-scavenging activity at concentrations as low as 3.3μmol/L. In addition, the 16S rRNA gene sequence （1401 bp） of the bacterium strain AUH-JLC257 showed the highest similarity （99.27%） to that of Slackia equolifaciens strain DZE.
