Through metabolic pathway engineering, novel microbial biocatalysts can be engineered to convert renewable resources into useful chemicals, including monomer building-blocks for bioplastics production. Here we describe the systematic engineering of Escherichia coli to produce, as individual products, two 5-carbon polyamide building blocks, namely 5-aminovalerate (AMV) and glutarate. The modular pathways were derived using "parts" from the natural lysine degradation pathway of Pseudomonas putida KT2440. Endogenous over-production of the required precursor, lysine, was first achieved through metabolic deregulation of its biosynthesis pathway by introducing feedback resistant mutants of aspartate kinase III and dihydrodipicolinate synthase. Further disruption of native lysine decarboxylase activity (by deleting cadA and ldcC) limited cadaverine by-product formation, enabling lysine production to 2.25 g/L at a glucose yield of 138 mmol/mol (18% of theoretical). Co-expression of lysine monooxygenase and 5-aminovaleramide amidohydrolase (encoded by davBA) then resulted in the production of 0.86 g/L AMV in 48 h. Finally, the additional co-expression of glutaric semialdehyde dehydrogenase and 5-aminovalerate aminotransferase (encoded by davDT) led to the production of 0.82 g/L glutarate under the same conditions. At this output, yields on glucose were 71 and 68 mmol/mol for AMV and glutarate (9.5 and 9.1% of theoretical), respectively. These findings further expand the number and diversity of polyamide monomers that can be derived directly from renewable resources.

By applying metabolic engineering tools and strategies to engineer synthetic enzyme pathways, the number and diversity of commodity and specialty chemicals that can be derived directly from renewable feedstocks is rapidly and continually expanding. This of course includes a number of monomer building-block chemicals that can be used to produce replacements to many conventional plastic materials. This review aims to highlight numerous recent and important advancements in the microbial production of these so-called “biomonomers.” Relative to naturally-occurring renewable bioplastics, biomonomers offer several important advantages, including improved control over the final polymer structure and purity, the ability to synthesize non-natural copolymers, and allowing products to be excreted from cells which ultimately streamlines downstream recovery and purification. To highlight these features, a handful of biomonomers have been selected as illustrative examples of recent works, including polyamide monomers, styrenic vinyls, hydroxyacids, and diols. Where appropriate, examples of their industrial penetration to date and end-product uses are also highlighted. Novel biomonomers such as these are ultimately paving the way toward new classes of renewable bioplastics that possess a broader diversity of properties than ever before possible.