Polyhydroxyalkanoates as multifaceted biopolymers: an eco-friendly alternative to conventional plastics

Plastic pollution originating from fossil-based materials persists as a critical environmental concern due to their resistance to degradation, as well as their role in the build-up of microplastics and the release of greenhouse gases across waste-management processes. Polyhydroxyalkanoates (PHAs) are considered effective, biodegradable and bio-based alternatives. However, financial and process constraints limit the industrial-scale use of PHAs despite considerable investigations. Several bacteria can synthesise PHAs using different substrates and store them as granules under nutrient-limited conditions. Bacterial species such as Bacillus, Pseudomonas, Halomonas and Cupriavidus necator have been used to produce PHAs. This study provides an analytical and comprehensive evaluation of PHAs as multifaceted biopolymers, evaluating existing developments and highlighting major constraints. This review evaluates comparatively different feedstocks for microbial production and optimisation approaches, highlighting their effectiveness and limitations. It further evaluates developments in metabolic engineering, including CRISPR/Cas9-mediated genome editing systems, bridge recombination, and synthetic biological engineering, which aim to increase yield and modify monomer characteristics. Moreover, it evaluates downstream processing techniques, such as chemical, enzymatic, mechanical and biological extraction methods, emphasising their sustainability and scalability. Significantly, this review highlights key barriers to the large-scale production of PHA, such as high manufacturing costs, variation in raw materials, and operational limitations while suggesting a strategic pathway for future research. Finally, this paper offers an integrated viewpoint that connects the production, properties, and applications of PHAs, providing the understanding necessary to enhance their relevance as sustainable alternatives to conventional plastics.