Biotransformation of Indole to Indigo by the Whole Cells of Phenol Hydroxylase Engineered Strain in Biphasic Systems

Biotransformation of indole to indigo in liquid–liquid biphasic systems was performed in Escherichia coli cells expressing phenol hydroxylase. It was suggested that indole could inhibit the cell growth even at low concentration of 0.1 g/L. The critical Log P for strain PH_ IND was about 5.0. Three different solvents, i.e., decane, dodecane, and dioctyl phthalate, were selected as organic phase in biphasic media. The results showed that dodecane gave the highest yield of indigo (176.4 mg/L), which was more than that of single phase (90.5 mg/L). The optimal conditions for biotransformation evaluated by response surface methodology were as follows: 540.26 mg/L of indole concentration, 42.27 % of organic phase ratio, and 200 r/min of stirrer speed; under these conditions, the maximal production of indigo was 243.51 mg/L. This study proved that the potential application of strain PH_ IND in the biotransformation of indole to indigo using liquid–liquid biphasic systems.