Harnessing in vivo Synthesis of Bioactive Multiarylmethanes in Escherichia coli via Oxygen-Mediated Free Radical Reaction Induced by Simple Phenols

BackgroundXanthenes and multi-aryl carbon core containing compounds represent different types of complex and condensed architectures that have impressive wide range of pharmacological, industrial and synthetic applications. Moreover, indoles as building blocks were only found in naturally occurring metabolites with di-aryl carbon cores and in chemically synthesized tri-aryl carbon core containing compounds. Up to date, rare xanthenes with indole bearing multicaryl carbon core have been reported in natural or synthetic products. The underlying mechanism of fluores-cein-like arthrocolins with tetra-arylmethyl core were synthesized in an engineered Escherichia coli fed with toluquinol remained unclear. ResultsIn this study, the Keio collection of single gene knockout strains of 3901 mutants of E. coli BW25113, together with 14 distinct E. coli strains, was applied to explore the origins of endoge-nous building blocks and the biogenesis for arthrocolin assemblage. Deficiency in bacterial res-piratory and aromatic compound degradation genes ubiX, cydB, sucA and ssuE inhibited the mu-tant growth fed with toluquinol. Metabolomics of the cultures of 3897 mutants revealed that only disruption of tnaA involving in transforming tryptophan to indole, resulted in absence of arthro-colins. Further media optimization, thermal cell killing and cell free analysis indicated that a non-enzyme reaction was involved in the arthrocolin biosynthesis in E. coli. Evaluation of redox potentials and free radicals suggested that an oxygen-mediated free radical reaction was respon-sible for arthrocolins formation in E. coli. Regulation of oxygen combined with distinct phenol derivatives as inducer, 31 arylmethyl core containing metabolites including 13 new and 8 biolog-ical active, were isolated and characterized. Among them, novel arthrocolins with p-hydroxylbenzene ring from tyrosine were achieved through large scale of aerobic fermentation and elucidated x-ray diffraction analysis. Moreover, most of the known compounds in this study were for the first time synthesized in a microbe instead of chemical synthesis. Through feeding the rat with toluquinol after colonizing the intestines of rat with E. coli, arthrocolins also ap-peared in the rat blood. ConclusionOur findings provide a mechanistic insight into in vivo synthesis of complex and condensed ar-throcolins induced by simple phenols and exploits a quinol based method to generate endoge-nous aromatic building blocks, as well as a methylidene unit, for the bacteria-facilitated synthesis of multiarylmethanes.