Recent advances in microbial polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are polyesters of hydroxyalkanoates (HAs) synthesised by numerous bacteria as an intracellular carbon and energy storage compound. These are accumulated in the cytoplasm of cells. A number of bacteria including Alcaligenes, Pseudomonas, recombinant Escherichia coli and methylotrophs have been used for the production of PHAs and high productivities have been achieved. Production of PHA by transgenic plants has been demonstrated on a laboratory-scale and large-scale production will be feasible in the near future. By controlling the monomer composition of PHA, it has been indicated that the physical properties of polymers can be regulated to a great extent. Even though PHAs have been recognised as a good candidate for biodegradable polymers, their high production cost limits their industrial application. It is hoped that with improvement in fermentation and downstream processing techniques, development of new recombinant strains and large-scale production by transgenic plants will reduce the cost of production of PHAs thereby making them competitive with conventional plastics.