[Screening and identification of a bacterium capable of converting daidzein to S-equol].

To screen and identify a bacterium capable of converting daidzein to S-equol. We used antibiotics to limit unrelated bacterial growth and enrich the target bacteria, and isolated the aim bacterial strain from rat intestine. The metabolite of daidzein was tested by HPLC, MS and NMR. The taxonomic group of the strain was identified by 16S rDNA sequence analysis and phylogenetic tree; the strain's morphological and physiological biochemical characters were also tested. A gram-negative facultative bacterial strain LH-52 (JN861767) capable of transforming daidzein to S-equol was isolated. Basic Local Alignment Search Tool (BLAST) search of LH-52's 16S rDNA sequence on GenBank suggested that this strain has 99% similarity to that of Proteus mirabilis, the morphological and physiological biochemical characteristics of LH-52 also showed highly similarity to P. mirabilis. Based on these data, we identified LH-52 as P. mirabilis, and named it as P. mirabilis LH-52. The results of HPLC, MS and NMR suggested that the metabolite of daidzien was S-equol. Bacteria strain P. mirabilis LH-52 was the first reported facultative bacteria strain capable of converting daidzein to S-equol, and might be more suitable in industrial application than obligate anareobic bacterial strains.