Polyhydroxybutyrate (PHB) composites represent a promising sustainable solution to address the environmental challenges posed by conventional polymers across multiple sectors. This comprehensive review synthesizes current knowledge on PHB-based composites, examining their development, performance, and biodegradation characteristics in diverse applications such as packaging, biomedical devices, agriculture, aerospace, and environmental remediation. Various composite fabrication methods, including melt blending, solution casting, electrospinning, and in situ polymerization, are evaluated for their impact on functional properties. Natural fiber- and nanomaterial-reinforced PHB composites are critically analyzed for their mechanical integrity, thermal stability, surface chemistry, biodegradability, and environmental compatibility. Practical challenges, including manufacturing scalability, cost-effectiveness, and long-term stability in complex environments, are discussed within circular economy and regulatory frameworks to situate PHB composites for realistic industrial and environmental deployment. This review provides timely insights for researchers and practitioners aiming to develop environmentally compatible, scalable biopolymer-based solutions across multiple domains.

Polyhydroxybutyrate (PHB) is a biodegradable polyester considered a sustainable alternative to petroleum-based plastics. However, its biodegradation in the presence of plasticizers remains poorly defined. This study investigated the impact of phthalate ester- and glycol-based plasticizers on PHB degradation by Ralstonia sp. C1. Real Time -Polymerase Chain Reaction(RT-PCR) analysis showed that expression of the PHB depolymerase gene phaZa1 remained unchanged in all additive-treated cultures, indicating no transcriptional interference. Liquid-medium degradation assays quantified by HPLC revealed rapid PHB utilization, with more than 50% degraded within 24 h and over 98% degraded within 48 h, with no significant differences relative to the control. Growth-inhibition assays further demonstrated that none of the plasticizers impaired bacterial viability, as OD₆₀₀ profiles were comparable to untreated cultures. Soil degradation experiments confirmed that PHB films containing additives decomposed at rates similar to additive-free films, reaching approximately 80% degradation within 10 weeks. Overall, the tested plasticizers did not affect enzyme expression, microbial activity, or PHB biodegradation, highlighting the suitability of plasticized PHB materials for environmentally sustainable applications and supporting their scalable use as biodegradable alternatives to conventional plastics.

The removal of heavy oil under low-temperature conditions is a significant global challenge. This study aimed to assess the long-term whole-cell biocatalytic degradation of heavy oil in water and soil by bacteria isolated from contaminated soil in Muroran, Japan, under cold conditions. Enrichment cultures using heavy oil as the sole carbon source yielded 15 potent heavy oil-degrading isolates. However, only the C1 strain retained its activity under low-temperature conditions and was identified as Pseudomonas aeruginosa C1 using 16S rDNA sequencing. Gas chromatography analysis revealed that at 30 °C (water medium), strain C1 degraded 57% of heavy oil within 7 days. At 15 °C, the degradation efficiency of C1 declined due to a temperature-dependent metabolic lag phase (1 day); however, at 15 °C, 70% degradation was observed in seven days. In long-term experiments at 5 °C and 10 °C, 35% and 40% degradation were recorded for C1 after 98 days. In artificially contaminated soil at 5 °C, C1 achieved 60% biodegradation. These results demonstrate cold-adapted whole-cell activity against heavy oil and motivate the design of controlled, contained ex situ reactors (e.g., enzyme-based or cell-free systems) for safe remediation in cold climates.