Production of microbial polyesters: fermentation and downstream processes

Poly(3-hydroxyalkanoates) (PHAs) constitute a large and versatile family of polyesters produced by various bacteria. PHAs are receiving considerable attention because of their potential as renewable and biodegradable plastics, and as a source of chiral synthons since the monomers are chiral. Industrial PHA production processes have been developed for poly(3-hydroxybutyrate) (poly(3HB)) and poly(3-hydroxybutyrate-co-3-valerate) (poly(3HB-co-3HV). More than 100 other poly(3HAMCL)s, characterized by monomers of medium chain length, have been identified in the past two decades. These monomers typically contain 6-14 carbon atoms, are usually linked via-3-hydroxy ester linkages, but can occasionally also exhibit 2-, 4-, 5-, or 6-hydroxy ester linkages. Such polyesters are collectively referred to as medium chain length PHAs poly(3HAMCL)s. The vast majority of these interesting biopolyesters have been studied and produced only on the laboratory scale. However, there have been several attempts to develop pilot scale processes, and these provide some insight into the production economics of poly(3HAMCL)s other than poly(3HB) and poly(3HB-co-3HV). These processes utilize diverse fermentation strategies to control the monomer composition of the polymer, enabling the tailoring of polymer material properties to some extent. The best studied of these is poly(3-hydroxyoctanoate) (poly(3HO)), which contains about 90% 3-hydroxyoctanoate. This biopolyester has been produced on the pilot scale and is now being used in several experimental applications.