Towards high-performance polyesters from carbon dioxide: novel polyhydroxyarylates from engineered Cupriavidus necator

Abstract

Synthetic materials are integral components of consumable and durable goods and are indispensable in the modern world. Polyesters are the most versatile bulk- and specialty-polymers but their production is not sustainable and their fate at end-of-life is of great concern. Bioplastics are highly regarded alternatives but often fall behind conventional synthetic plastics due to shortcomings in material properties and commercial competitiveness. This has limited the success of sustainable replacements at global market scale. Enabling production of bioplastics with superior properties from waste-derived feedstocks could change that. To this end, we created a synthetic entry into the metabolic pathway of bio-polyester synthesis of Cupriavidus necator H16 by means of heterologous hydroxyacyl-CoA transferase and mutant PHA synthase. The resulting microbial cell factories produced a range of aliphatic and aromatic bio-polyesters and enabled co-polymerization of a range of hydroxy carboxylates, including a hydroxyphenylic and a hydroxyfuranoic acid, for the first time incorporating aromatic rings in the backbone of biological polyesters. These diverse polymers were then characterized in terms of their physical properties. The resulting polymers were structurally analogous to synthetic polyesters like PET, PEF and other polyarylates. In a further advance, the transgenic strain was cultivated in a bio-electrochemical system under autotrophic conditions, enabling synthesis of aromatic bio-polyesters from in-situ generated O2, while assimilating CO2. Follow-up elementary flux-mode analysis established the feasibility of de-novo production of twenty different polyesters from five different carbon- and energy-sources. This comprehensive study opens the door to sustainable bio-production of various high-performance thermoplastics and thermosets.