TABLE OF CONTENTS Kumar Sudesh and Yoshiharu Doi
Polyhydroxyalkanoates (PHA) is the term given to a family of polyesters produced by microorganisms. The most well known among them is the thermoplastic poly[ R-3-hydroxybutyrate] (P[3HB]). In this chapter, an attempt has been made to summarise the present state of research and development of these interesting microbial polyesters. Several types of PHA homopolymers and copolymers with useful physical properties have been identified. It is now possible to tailor-make these PHA using suitable carbon sources in both wild type and/or recombinant microorganisms. The basic principles underlying the biosynthesis of various PHA will be emphasised. This will include the major biochemical pathways involved in the conversion of various carbon sources into suitable monomers that are polymerised by the key enzyme of PHA biosynthesis, PHA synthase. In addition, the development of various potential methods for the large-scale production of PHA will be compared. The most attractive property of PHA is its biodegradability, which is a crucial factor in today s polymer technology. Accordingly, this chapter will also include a brief overview on the biodegradation of PHA as well as the mechanisms involved. Finally, the many new potential applications of PHA especially in the medical field will be discussed.
In conditions of excess nutrients, many microorganisms usually assimilate and store them for future consumption [1]. Various storage materials have been identified in microorganisms, which include glycogen, sulfur, polyamino acids, polyphosphate, and lipids [2]. PHA are lipoidic material [3] accumulated by a wide variety of microorganisms in the...
