Characterization of a Novel Phenol Hydroxylase in Indoles Biotranformation from a Strain <em>Arthrobacter</em> sp. W1

<div><h3>Background</h3><p>Indigoids, as popular dyes, can be produced by microbial strains or enzymes catalysis. However, the new valuable products with their transformation mechanisms, especially inter-conversion among the intermediates and products have not been clearly identified yet. Therefore, it is necessary to investigate novel microbial catalytic processes for indigoids production systematically.</p> <h3>Findings</h3><p>A phenol hydroxylase gene cluster (4,606 bp) from <em>Arthrobacter</em> sp. W1 (PH_w1) was obtained. This cluster contains six components in the order of <em>KLMNOP</em>, which exhibit relatively low sequence identities (37–72%) with known genes. It was suggested that indole and all the tested indole derivatives except for 3-methylindole were transformed to various substituted indigoid pigments, and the predominant color products derived from indoles were identified by spectrum analysis. One new purple product from indole, 2-(7-oxo-1H-indol-6(7H)-ylidene) indolin-3-one, should be proposed as the dimerization of isatin and 7-hydroxylindole at the C-2 and C-6 positions. Tunnel entrance and docking studies were used to predict the important amino acids for indoles biotransformation, which were further proved by site-directed mutagenesis.</p> <h3>Conclusions/Significance</h3><p>We showed that the phenol hydroxylase from genus <em>Arthrobacter</em> could transform indoles to indigoids with new chemical compounds being produced. Our work should show high insights into understanding the mechanism of indigoids bio-production.</p>