A microbial platform for recyclable plastics with customizable properties

<title>Abstract</title> Plastics have played a crucial role in shaping the modern era. However, they are produced almost exclusively from non-renewable feedstocks and face considerable challenges in recycling, especially crosslinked polymers used in consumer electronics, building materials, automotive parts, and aerospace composites1–3. Here, we integrate computational materials design, polymer chemistry, synthetic biology, and systems analysis into a workflow to accelerate the design of biorenewable polydiketoenamines (bioPDKs) with tailored properties and circularity through molecular engineering of their monomers, which are derived from β-keto-δ-lactones (BKDLs). Our approach leverages the modular assembly of hybrid polyketide synthases (PKSs) to enable the biosynthesis of BKDLs with diverse substituents at the γ- and δ-positions with defined stereochemistry. We exploit these features to tailor bioPDK hydrophobicity and depolymerization temperature in aqueous acid, which would be nearly impossible to do at scale using synthetic chemistry. In specific designs, we observe increases in bioPDK acidolysis above thresholds for comparable PDK materials derived from petrochemicals, which has implications for mixed-plastic and composite recycling, solvent and chemical resistance, and degradation.