Biotransformation of flavone and flavanone by Streptomyces lividans cells carrying shuffled biphenyl dioxygenase genes

The bphA1(2072)A2A3A4 gene cluster codes for a shuffled biphenyl dioxygenase holoenzyme with broad substrate specificity. The bphA1(2072) encoding the large subunit of an iron–sulfur protein is a hybrid gene generated by DNA shuffling using bphA1 of Pseudomonas pseudoalcaligenes KF707 and bphA1 of Burkholderia cepacia LB400. The bphA2 encoding the small subunit of an iron–sulfur protein, bphA3 encoding a ferredoxin and bphA4 encoding a ferredoxin reductase are from P. pseudoalcaligenes KF707. The bphA1(2072)A2A3A4 gene cluster was positioned downstream of a thiostrepton-inducible promoter PtipA on a high-copy-number vector pIJ6021, and introduced into the Gram-positive, soil-inhabiting, filamentous bacterium Streptomyces lividans. Biotransformation of some flavonoids by the recombinant S. lividans cells was examined and the products were determined by EI-MS, 1H and 13C NMR. Flavone was converted into two products, 2′,3′-dihydroxyflavone (a major product) and 3′-hydroxyflavone (a minor product). Flavanone was converted into three products, 2′,3′-dihydroxyflavanone (a major product), 2′-hydroxyflavanone and 3′-hydroxyflavanone (minor products). 2′,3′-Dihydroxyflavanone was a novel compound. The biotransformation of flavone and flavanone proceeded very efficiently; 1 mM of each of the substrate was almost completely converted to the corresponding di- or mono-hydroxy form in 24 h. Furthermore, 6-hydroxyflavone and 6-hydroxyflavanone were also converted into 2′,6-dihydroxyflavone and 3′,6-dihydroxyflavanone, respectively. Among these products, 2′,3′-dihydroxyflavone and 2′,3′-dihydroxyflavanone showed free radical-scavenging activity.