Enzymatic and microbial routes to bioplastics: The green chemistry frontier of biopolymers

The rapid escalation of global plastic consumption, coupled with the environmental impacts of petrochemical polymers, has sparked a surge of interest in bioplastics, particularly those derived from microbial and enzymatic processes. This review provides a comprehensive overview of the metabolic pathways, structural properties and emerging technological innovations shaping the next generation of bioplastics, with a particular focus on polyhydroxyalkanoates (PHA). The following sections outline the conceptual distinctions between bio-based and biodegradable plastics, the key bacterial pathways responsible for the biosynthesis of PHA, PLA precursors, bacterial cellulose, microbial polyamides and other bio-derived polymers. The physicochemical and morphological features of PHA-based materials are analysed as well. These features include monomer composition, crystallinity, copolymer architecture and molecular weight. The relationship between these features and the mechanical and thermal performance of the materials is then investigated. A dedicated section is allocated to recent advances in in vitro enzymatic PHA synthesis, covering PHA synthase (PhaC) classes, engineered variants, cell-free metabolic engineering platforms, enzyme immobilisation and surface-display strategies that enable fully programmable and modular polymerisation. Finally, we discuss future perspectives, with particular emphasis on sustainable feedstocks, process intensification through synthetic biology, techno-economic challenges and the regulatory landscape required for large-scale adoption. The present review integrates biochemical, structural and bioprocessing insights to map current progress and identify strategic directions for enabling enzymatic bioplastics as scalable, customisable and environmentally sound alternatives within a circular bioeconomy framework. Impact statement This review highlights recent advances in microbial and enzymatic routes for producing polyhydroxyalkanoate-based bioplastics, with emphasis on engineered enzymes and cell-free systems. By integrating biochemical and bioprocess insights, it outlines strategies to enable scalable and sustainable biopolymer production within a circular bioeconomy.