Caenorhabditis elegans （C. elegans） was used as an animal model to study the effect of （-）-5-hydroxy-equol, a microbialmetabolite of isoflavone genistein, on the lifespan, fecundity and resistance against thermal and oxidative stress. The resultsshowed that （-）-5-hydroxy-equol not only significantly increased the lifespan of C. elegans but also significantly enhancedthe resistance against thermal and oxidative stress at the concentrations of 0.1 mmol/L and 0.2 mmol/L. However, the fecundityof C. elegans was not obviously influenced after being exposed to the same concentrations of （-）-5-hydroxy-equol. Further studieson comparative transcriptome analyses and the lifespan ofdaf-16 （mu86） mutant and daf-2 （e1370） mutant indicated that（-）-5-hydroxy-equol prolonged the lifespan of C. elegans through DAF-2/DAF-16 Insulin/IGF-1 signaling pathway. This isthe first report that （-）-5-hydroxy-equol was able to increase the lifespan and improve the thermal and oxidative stress toleranceof C. elegans.
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.
