Polyhydroxyalkanoates as ecological currencies across the microbial tree of life

Polyhydroxyalkanoates (PHAs) are a diverse family of intracellular polyesters synthesized by bacteria and archaea across a wide array of metabolic and ecological contexts. Originally characterized as inert carbon and energy reserves, PHAs are now recognized as multifunctional biopolymers with dynamic roles in redox homeostasis, stress mitigation, and microbial community interactions. This review presents a comprehensive synthesis of the current understanding of PHA metabolism-from canonical biosynthetic enzymes and granule-associated structural proteins to diverse regulatory circuits and pathway variants. We highlight recent discoveries in anaerobic and facultative aerobic PHA producers, uncover emerging patterns in ecological function, and integrate novel computational approaches-including Hidden Markov Models, protein language models, and AI-guided enzyme design-for functional gene discovery. Special attention is given to the redox buffering capacity of PHA granules, their role in stress resilience, and their contribution to microbial fitness in fluctuating environments. Finally, we examine the techno-economic landscape of microbial PHA production, the application of PHA-derived materials in biomedical and industrial contexts, and the broader implications for sustainable biopolymer design. This review synthesizes recent advances in PHA biology, reframing these polymers from inert carbon and energy depots to active, dynamic participants in microbial physiology, integrating redox homeostasis, metabolic flux regulation, and adaptive stress responses.