Metabolic pathway design for BTEX-based commodity chemicals: drop-ins and alternatives

BTEX (i.e. benzene, toluene, ethylbenzene, and xylene) compounds are critical petroleum-sourced precursors for other aromatic commodity chemicals, all of which are ubiquitous starting materials in organic synthesis. To reduce society's carbon footprint and dependence on petroleum, microbial chassis may be engineered with heterologous metabolic pathways to bioproduce these same bulk aromatics, or structural analogs thereof, from renewable carbon sources. This review chiefly examines the latest developments in microbial metabolic pathway design and engineering for the bioproduction of bulk aromatics conventionally made from BTEX. Herein, we discuss metabolic routes to both bio-aromatic drop-ins (styrene, benzoic acid, and even the fundamental BTEX compounds), as well as bio-aromatic alternatives of xylene-derived diacids (pyridine- and furandicarboxylic acids).