Polyhydroxyalkanoates (PHA), a family of biopolyesters with diverse structures,
are the only bioplastics completely synthesized by microorganisms. PHA can be
synthesized by over 30% of soil-inhabiting bacteria (Wu et al. 2000). Many bacteria
in activated sludge, in high seas, and in extreme environments are also capable of
making PHA. In the last 10 years, PHA have been developed rapidly to find applications
in various fields (Fig. 1) (Chen 2009a).
PHA have rich properties depending on the structures (Figs. 2, 3). Homopolymers,
random copolymers, and block copolymers of PHA can be produced depending on the
bacterial species and growth conditions. With over 150 different PHA monomers
being reported, PHA with flexible thermal and mechanical properties have been
developed (He et al. 1999). Such diversity has allowed the development of various
applications, including environmentally friendly biodegradable plastics for packaging
purposes, fibers, biodegradable and biocompatible implants, and controlled drug