Engineering of biological systems for the synthesis of tailor-made polyhydroxyalkanoates, a class of versatile polymers

Medium-chain-length polyhydroxyalkanoates (mcl-PHAs) are bacterial polyeste rs which are produced in nature by certain Pseudomonas strains. These biopo lymers are of interest because of their chirality, biodegradability and ela stomeric property, while the 3-hydroxy acid monomers are a potential source of chiral synthons. Since wild-type bacteria can only be used to a limited extent for the production of tailor-made functionalized PHAs, various reco mbinant bacteria have been generated in order to elucidate the PHA synthesi s pathway and to control and modify the metabolic carbon flux towards PHA s ynthesis. Production of PHAs with altered monomer composition and physical properties has already been achieved by pathway engineering. An alternative to the in vivo synthesis strategies using whole microorganisms is PHA synt hesis in vitro with isolated enzymes, which is of interest for incorporatio n of specific monomers that are not taken up or metabolized by bacterial ce lls. The various synthesis strategies are discussed in the context of the p ossible future production of tailor-made functionalized PHAs.