Identification of an indole biodegradation gene cluster from and its contribution in selectively biosynthesizing Tyrian purple.

Tyrian purple, mainly composed of 6, 6'-dibromoindigo, is a precious dye extracted from sea snails. In this study, we found Tyrian purple can be selectively produced by a bacterial strain GS-2 when fed with 6-bromotryptophan in the presence of tryptophan. This GS-2 strain was then identified as based on bacterial genome sequencing analysis. An indole degradation gene cluster for indole metabolism was identified from this GS-2 strain. The heterologous expression of the indole degradation gene cluster in BL21 (DE3) and enzymatic reaction demonstrated that the indole biodegradation gene cluster may contribute to selectively biosynthesizing Tyrian purple. To further explore the underlying mechanism of the selectivity, we explored the intermediates in this indole biodegradation pathway using liquid chromatography electrospray ionization quadrupole time-of-flight mass spectrometry (LC-ESI-QTOF-MS/MS), which indicated that the indole biodegradation pathway in is the catechol pathway. Interestingly, the monooxygenase -C co-expressed with its corresponding reductase -D in the cluster has better activity for the biosynthesis of Tyrian purple compared with the previously reported monooxygenase from (MaFMO) or cytochrome P450 enzyme (CYP102G4). This is the first study to show the existence of an indole biodegradation pathway in , and the indole biodegradation gene cluster can contribute to the selective production of Tyrian purple.