(41a) Comparison of Non-Natural Pathways for Phenol Biosynthesis in Engineered Escherichia Coli

The non-renewable petrochemical phenol is used as a precursor to produce numerous fine and commodity chemicals (e.g., bisphenol A, caprolactam, and salicylic acid) as well as materials such as phenolic resins.  A renewable route to phenol from glucose-derived tyrosine via tyrosine phenol lyase has previously been demonstrated using engineered Pseudomonas putida as the biocatalyst.  In contrast, here we present on the development of a novel pathway that converts chorismate to phenol via the concerted action of isochorismate synthase, isochorismate pyruvate lyase, and salicylate decarboxylase.  Whereas the former route involves fewer heterologous steps, it is derived from an endogenous precursor further removed from the central metabolism.  Although both pathways have identical theoretical yields, comparison of the two routes provides interesting insight into pathway design strategies for non-natural chemical production.  Both routes were systematically constructed in Escherichia coli following screening studies to identify the most robust pathway enzymes resulting in initial shake flask titers of 25 mg/L.  Current strategies to increase final product titers through both routes include pathway de-bottlenecking by development of optimal expression strategies and re-engineering of the host metabolism to maximize production and availability of respective precursors.