A Review of Polyhydroxybutyrate Biosynthesis by Different Microorganisms.

Polyhydroxybutyrate (PHB) production from renewable biomass feedstocks using microorganisms provides a sustainable alternative to petroleum-based plastics, addressing critical challenges such as plastic pollution and fossil fuel consumption. Unlike previous reviews that primarily focus on single genera or metabolic mechanisms, this review provides a comprehensive comparison of multiple microbial platforms, emphasizing strain selection strategies, genetic engineering approaches, and substrate flexibility, particularly for waste valorization. Bacterial systems, while efficient, are limited by the high cost of sterile conditions. Engineered yeasts and fungi offer resilience to industrial stresses but face metabolic constraints. In addition, haloarchaeal extremophiles have gained attention for PHB synthesis under high-salinity, nonsterile conditions, offering unique advantages for cost-effective bioprocessing. Photosynthetic microorganisms integrate CO₂ capture with PHB synthesis but face challenges like slow growth rates and low yields. Mixed microbial cultures provide a cost-effective approach by utilizing low-cost substrates under nonsterile conditions, though optimizing enrichment strategies remain essential to improving productivity. Future directions highlight the significance of evaluating strain selection strategies, advancing genetic engineering approaches, and scaling up production processes. Additionally, assessing technoeconomic viability and life-cycle environmental impact is crucial to support the development of PHB as a scalable, cost-effective, and environmentally friendly solution for the circular economy.