Microbial synthesis of stereoirregular PHB

PHB is a biodegradable alternative to petroleum-based plastics, but its broad commercial adoption is limited by poor material properties. Natural microbial PHB is strictly (R)-isotactic, causing crystallinity and brittleness. PHB’s high melting point overlaps with its thermal degradation temperature, causing molecular weight degradation during thermal processing and complicating recycling. While chemical synthesis can produce more flexible, stereoirregular PHB, it remains industrially uncompetitive.

This new microbial synthesis route enables the direct production of stereoirregular PHB via fermentation in recombinant microorganisms. Overturning the long-held assumption that PHA synthases are strictly stereoselective, this technology successfully incorporates both (R)- and (S)-3-hydroxybutyrate monomers into the polymer chain. This breakthrough bridges the gap between the superior material properties of chemically synthesized PHB and the cost-effective, sustainable scalability of microbial synthesis.