Abstract
Phenol is an important petrochemical that is conventionally used as a precursor for synthesizing an array of plastics and fine chemicals. As an emerging alternative to its traditional petrochemical production, multiple enzyme pathways have been engineered to date to enable its renewable biosynthesis from biomass feedstocks, each incorporating unique enzyme chemistries and intermediate molecules. Leveraging all three of the unique phenol biosynthesis pathways reported to date, a series of synthetic 'metabolic funnels' was engineered, each with the goal of maximizing net precursor assimilation and flux towards phenol via the parallel co-expression of multiple distinct pathways within the same Escherichia coli host. By constructing and evaluating all possible binary and tertiary pathway combinations, one 'funnel' was ultimately identified, which supported enhanced phenol production relative to all three individual pathways by 16 to 69%. Further host engineering to increase endogenous precursor availability then allowed for 26% greater phenol production, reaching a final titer of 554 +/- 19 mg/L and 28.8 +/- 0.34 mg/g yield on glucose. Lastly, using a diphasic culture including dibutyl phthalate for in situ phenol extraction, final titers were further increased to a maximum of 812 +/- 145 mg/L at a yield of 40.6 +/- 7.2 mg/g. The demonstrated 'funneling' pathway holds similar promise in support of phenol production by other, non-E. coli hosts, while this general approach can be readily extended towards a diversity of other value-added bioproducts of interest.