Microbial Upcycling of Waste PET to Adipic Acid.

Microorganisms can be genetically engineered to transform abundant waste feedstocks into value-added small molecules that would otherwise be manufactured from diminishing fossil resources. Herein, we report the first one-pot bio-upcycling of PET plastic waste into the prolific platform petrochemical and nylon precursor adipic acid in the bacterium Escherichia coli. Optimizing heterologous gene expression and enzyme activity enabled increased flux through the de novo pathway, and immobilization of whole cells in alginate hydrogels increased the stability of the rate-limiting enoate reductase BcER. The pathway enzymes were also interfaced with hydrogen gas generated by engineered E. coli DD-2 in combination with a biocompatible Pd catalyst to enable adipic acid synthesis from metabolic cis,cis-muconic acid. Together, these optimizations resulted in a one-pot conversion to adipic acid from terephthalic acid, including terephthalate samples isolated from industrial PET waste and a post-consumer plastic bottle.

One-Pot Synthesis of Adipic Acid from Guaiacol in Escherichia coli.

Adipic acid is one of the most important small molecules in the modern chemical industry. However, the damaging environmental impact of the current industrial synthesis of adipic acid has necessitated the development of greener, biobased approaches to its manufacture. Herein we report the first one-pot synthesis of adipic acid from guaiacol, a lignin-derived feedstock, using genetically engineered whole-cells of Escherichia coli. The reaction is mild, efficient, requires no additional additives or reagents, and produces no byproducts. This study demonstrates how modern synthetic biology can be used to valorize abundant feedstocks into industrially relevant small molecules in living cells.

Transition Metal-Free Reduction of Activated Alkenes Using a Living Microorganism.

Microorganisms can be programmed to perform chemical synthesis via metabolic engineering. However, despite an increasing interest in the use of de novo metabolic pathways and designer whole-cells for small molecule synthesis, the inherent synthetic capabilities of native microorganisms remain underexplored. Herein, we report the use of unmodified E. coli BL21(DE3) cells for the reduction of keto-acrylic compounds and apply this whole-cell biotransformation to the synthesis of aminolevulinic acid from a lignin-derived feedstock. The reduction reaction is rapid, chemo-, and enantioselective, occurs under mild conditions (37 °C, aqueous media), and requires no toxic transition metals or external reductants. This study demonstrates the remarkable promiscuity of central metabolism in bacterial cells and how these processes can be leveraged for synthetic chemistry without the need for genetic manipulation.