Biotransformation of indole by whole cells of recombinant biphenyl dioxygenase and biphenyl-2,3-dihydrodiol-2,3-dehydrogenase

► The bphAB genes were cloned from Dyella ginsengisoli LA-4 and expressed in Escherichia coli. ► The feasibility of indole transformation was predicted by molecular docking studies. ► A maximum indigo yield of 44mg/L was produced from 200mg/L indole. ► The products during indole transformation were identified by HPLC–MS. ► The pathway of indole transformation by strain AB_IND was proposed. The introduction of hydroxyl groups into indole molecule by different mono- and dioxygenases leads to the production of indigo. As a well-known biocatalyst, biphenyl dioxygenase possessed the ability to transform indole to indigo. However, there has been little information about this enzymatic transformation process. In this study, the genes encoding biphenyl dioxygenase (BphA) and biphenyl-2,3-dihydrodiol 2,3-dehydrogenase (BphB) were cloned from Dyella ginsengisoli LA-4 and heterologously expressed in Escherichia coli (DE3) (designated as AB_IND). The feasibility of indole transformation to indigo by strain BphA_LA-4 was predicted by molecular docking studies. The biotransformation ratios of indole (100mg/L) reached the maximum (95%) when cells were induced at 15°C with 0.25mM IPTG in M9 medium. In addition, 44mg/L indigo was produced from 200mg/L indole when supplied with 0.28g/L of biomass and 0.2% (w/v) glucose. HPLC–MS was used to identify the products, which showed that indigo was the major product. Meanwhile, indirubin and isatin were also identified during the transformation process. Furthermore, the pathway of indole transformation by strain AB_IND was also proposed.