Polyhydroxybutyrate (PHB) production from halophiles: a comprehensive review

The growing environmental impact of petroleum-based plastics has intensified the search for sustainable and biodegradable alternatives. Polyhydroxybutyrate (PHB), a microbial polyester from the polyhydroxyalkanoate (PHA) family, has emerged as a promising biopolymer due to its biodegradability, biocompatibility, and thermoplastic qualities that rival those of conventional polymers. Halophilic bacteria have attracted considerable attention among PHB-producing microorganisms because they thrive in hypersaline environments, enabling non-sterile cultivation, reducing contamination risks, and facilitating cost-effective downstream recovery by osmotic cell lysis. This review provides a comprehensive overview of recent improvements in PHB production by halophilic bacteria, covering physiological adaptations, metabolic pathways, substrate usage, fermentation techniques, and bioreactor optimisation. Particular emphasis is placed on the use of agro-industrial residues and waste-derived feedstocks as sustainable carbon sources to reduce production costs and increase circular bioeconomy results. Recent advances in downstream processing, such as green extraction technologies, metabolic engineering, CRISPR-based gene editing, and synthetic biology approaches to increasing PHB productivity, are critically reviewed. Additionally, developments in polymer modification, life cycle assessment, industrial scalability, regulatory frameworks, and potential applications in packaging, agriculture, and biomedical engineering are discussed. Despite significant progress, issues such as process economics, saline wastewater control, polymer brittleness, and large-scale commercialisation remain. Integrating halophilic biotechnology with waste valorisation, green recovery technologies, sophisticated metabolic engineering, and circular biorefinery concepts offers a promising strategy for developing economically and environmentally sustainable PHB production systems.