Abstract

Polyhydroxyalkanoates (PHA) occur naturally as water-insoluble inclusion bodies within the cytoplasm of a variety of bacteria. They have garnered global interest because they have properties similar to petrochemical-derived plastics, in addition to which they are also biodegradable and biocompatible, and are synthesized from renewable resources. The two main classes, short-chain-length PHA (PHA_SCL) and medium-chain-length PHA (PHA_MCL), are synthesized in non-pseudomonads and fluorescent pseudomonads, respectively, along different biosynthetic routes. The production of bacterial PHA by fermentation is well developed, the highest yield being obtained from recombinant strains. Nevertheless, the production cost of PHA is currently many times higher than petrochemical plastics which thus makes PHA economically unviable to be used for bulk commodities. There is, however, much potential for PHA to be used in biomedical applications. Areas of on-going R&D include improving the fermentation and recovery processes as means to increase PHA yield and reduce processing costs while developing processes that reduce negative impacts on the environment. In vitro biosynthesis using purified enzymes (eg, PHA synthase) and activated precursors (eg, 4-hydroxybutyryl-CoA), and the technology to effectively recycle the enzymes is another area of active study. The development of transgenic plants that produce PHA, like how starch and vegetable oils are produced, is widely believed to hold the key to viable large scale production of PHA at costs that allow the material to be used for common disposable products that are the major plastic pollutants.