Bacterial polyhydroxyalkanoates

TLDR

Polyhydroxyalkanoates (PHAs) are bacterial polyesters that serve as intracellular carbon and energy storage, comprising over 80 hydroxyalkanoate monomers that confer diverse mechanical properties, yet their high cost relative to conventional plastics limits widespread use. The study aims to reduce PHA production costs through advanced fermentation, separation technologies, and engineered strains or plants to make them competitive with conventional plastics. Advances in bacterial metabolism, genetics, and cloning of over 20 PHA biosynthesis genes have enabled recombinant strains and engineered plants to produce diverse polyesters with higher polymer accumulation. Several bacterial species and recombinant *E.

Abstract

Polyhydroxyalkanoates (PHAs) are polyesters of hydroxyalkanoates (HAs) synthesized by numerous bacteria as intracellular carbon and energy storage compounds and accumulated as granules in the cytoplasm of cells. More than 80 HAs have been detected as constituents of PHAs, which allows these thermoplastic materials to have various mechanical properties resembling hard crystalline polymer or elastic rubber depending on the incorporated monomer units. Even though PHAs have been recognized as good candidates for biodegradable plastics, their high price compared with conventional plastics has limited their use in a wide range of applications. A number of bacteria including Alcaligenes eutrophus, Alcaligenes latus, Azotobacter vinelandii, methylotrophs, pseudomonads, and recombinant Escherichia coli have been employed for the production of PHAs, and the productivity of greater than 2 g PHA/L/h has been achieved. Recent advances in understanding metabolism, molecular biology, and genetics of the PHA-synthesizing bacteria and cloning of more than 20 different PHA biosynthesis genes allowed construction of various recombinant strains that were able to synthesize polyesters having different monomer units and/or to accumulate much more polymers. Also, genetically engineered plants harboring the bacterial PHA biosynthesis genes are being developed for the economical production of PHAs. Improvements in fermentation/separation technology and the development of bacterial strains or plants that more efficiently synthesize PHAs will bring the costs down to make PHAs competitive with the conventional plastics.