Carbon cycle of polyhydroxyalkanoates (CCP): Biosynthesis and biodegradation.

Carbon neutrality of bioactive materials is vital in promoting sustainable development for human society. Polyhydroxyalkanoates (PHAs) is a class of typical carbon-cycle bio-polyesters synthesized by microorganisms using sugars, organic acids, and even carbon dioxide. PHAs first degrade into 3-hydroxybutyrate (3HB) before further breaking down into carbon dioxide and water, aligning with carbon-neutral goals. Due to their diverse molecular structures and material properties, excellent biocompatibility, and controlled biodegradability, PHAs have found widespread applications in environmental protection and biomedicine. However, challenges persist in achieving cost-effective PHA production and reusing degradation products. Additionally, understanding the carbon pathways in PHA synthesis and degradation remains limited. In this review, we first introduce the concept of the Carbon Cycle of Polyhydroxyalkanoates (CCP) and describe the biosynthetic pathways of aromatic monomers, carbon conversion processes, and PHA degradation in compost, soil, and marine environments. This will help us fully understand the sustainable utilization value of PHA as a biomaterial. Future trends point to integrating synthetic biology with emerging technologies to produce low-cost, high-value PHAs, supporting global green and low-carbon development.