polyhydroxyalkanoaten

Polyhydroxyalkanoates (PHAs) are a class of biopolyesters produced by many bacteria and some archaea as intracellular carbon and energy storage inclusions. They accumulate as granules in the cytoplasm under nutrient limitation with excess carbon and can be mobilized when needed.

PHAs consist of hydroxyalkanoate monomers linked by ester bonds. They are categorized by chain length: short-chain-length (scl) PHAs with 3–5 carbon atoms such as poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxyvalerate) (PHV); and medium-chain-length (mcl) PHAs with 6–14 carbons whose properties range from rigid to elastomeric. Copolymers and blends tailor mechanical and thermal properties, enabling a spectrum from stiff plastics to flexible elastomers.

Biosynthesis typically proceeds from acetyl-CoA. The enzymes PhaA (β-ketoacyl-CoA thiolase) and PhaB (acetoacetyl-CoA reductase) convert acetyl-CoA to 3-hydroxyacyl-CoA, which is polymerized by PhaC (PHA synthase) into polymer. PHA granules are stabilized by phasin proteins (PhaP) that regulate granule size and number. Degradation is carried out by PhaZ depolymerases, releasing monomers for cellular metabolism.

Industrial relevance and applications: PHAs are biodegradable and biocompatible, with potential use in packaging, disposable consumer products, agricultural films, and medical devices such as sutures and drug-delivery matrices. Production faces challenges related to cost, feedstock variability, and process optimization, though advances in metabolic engineering and bioprocessing are expanding viability.

Environmental and research context: As renewable bioplastics, PHAs attract interest for sustainable materials. Ongoing research seeks to broaden monomer types, tailor material properties, and reduce production costs to improve competitiveness with traditional plastics.