Biotransformation of soybean isoflavones by a marine Streptomyces sp 060524 and cytotoxicity of the products

A marine Streptomyces sp. 060524 capable of hydrolyzing the glycosidic bond of isoflavone glycosides, was isolated by detecting its beta-glucosidase activity. 5 isoflavone aglycones were isolated from culture filtrates in soybean meal glucose medium. They were identified as genistein (1), glycitein (2), daidzein (3), 3',4',5,7-tetrahydroxyisoflavone (4), and 3',4',7-trihydroxyisoflavone (5), based on UV, NMR and mass spectral analysis. The Streptomyces can selectively hydroxylate at the 3'-position in the daidzein and genistein to generate 3'-hydroxydaidzein and 3'-hydroxygenistein, respectively. The Strain biotransformed more than 90% of soybean isoflavone glycosides into their aglycones within 108 h. 3'-hydroxydaidzein and 3'-hydroxygenistein exhibited stronger cytotoxicity against K562 human chronic leukemia than daidzein and genistein.