Bacterial polyhydroxyalkanoates-eco-friendly next generation plastic: Production, biocompatibility, biodegradation, physical properties and applications

Polyhydroxyalkanoates (PHAs) are intracellular aliphatic polyesters synthesized as energy reserves, in the form of water-insoluble, nano-sized discrete and optically dense granules in cytoplasm by a diverse bacteria and some archae under conditions of limiting nutrients in the presence of excess carbon source. Bacteria synthesize different PHAs from coenzyme A thioesters of respective hydroxyalkanoic acid, and degrade intracellularly for reuse and extracellularly in natural environments by other microorganisms. In vivo, PHAs exist as amorphous mobile liquid and water-insoluble inclusions but in vitro, exhibit material and mechanical properties, ranging from stiff and brittle crystalline to elastomeric and molding, similar to petrochemical thermoplastics. Further, they are hydrophobic, isotactic, biocompatible and exhibit piezoelectric properties. But as commodity plastics their applications are limited by high production cost, low yield, in vivo degradation, complexity of technology and difficulty of extraction. Therefore, to replace the conventional plastic with PHAs, it is prerequisite to standardize the PHA production systems.