Bacterial Polyb ydroxyalkanoates

Bacterial Polyb ydroxyalkanoates

Bacterial Polyb ydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are polyesters of hy-
droxyalkanoates (HAS) synthesized by numerous bacte-
ria as intracellular carbon and energy storage com-
pounds and accumulated as granules in the cytoplasm of
cells. More than 80 HAS have been detected as constitu-
ents 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 applica-
tions. A number of bacteria including Alcaligenes eutro-
phus, Alcaligenes latus, Azotobacter vinelandii, methy-
lotrophs, pseudomonads, and recombinant Escherichia
coli have been employed for the production of PHAs, and
the productivity of greater than 2 g PHA/Uh has been
achieved. Recent advances in understanding metabo-
lism, molecular biology, and genetics of the PHA-
synthesizing bacteria and cloning of more than 20 differ-
ent PHA biosynthesis genes allowed construction of var-
ious recombinant strains that were able to synthesize
polyesters having different monomer units and/or to ac-
cumulate much more polymers. Also, genetically engi-
neered plants harboring the bacterial PHA biosynthesis
genes are being developed for the economical produc-
tion of PHAs. Improvements in fermentationkeparation
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 con-
ventional plastics. 0 1996 John Wiley & Sons, Inc.
Key words: polyhydroxyalkanoate poly(3-hydroxy-
butyrate) biodegradable plastic biopolymer fermen-
tation.

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