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Abstract
Polyhydroxyalkanoates (PHAs) are biologically produced polyesters which can consist of a diverse set of repeating unit structures. These biologically produced polyesters have many attractive properties and have been produced for use as bulk commodity plastics, fishing lines, and medical uses. PHAs have also attracted much attention as biodegradable polymers that can be produced from biorenewable resources. The cellular factories that produce these polymers offer the ability to produce or incorporate monomers that may not be available via typical chemical synthesis. In addition, cellular production of PHAs may be more “green” as compared to the use of specific metal catalysts for the production of polymers. The biosynthetic incorporation of specific monomers into PHA polymers is dependent on many factors that include the type of carbon source that the organism is grown on, the types of metabolic pathways available to that organism to convert those carbon sources into PHA monomers, and the substrate specificity of the enzymes involved in PHA synthesis. This review covers known biosynthetic pathways for the production of PHAs.
Notes
a Substrates preferred by the PHA synthase. SCL-HA-CoA (C3-C5), short-chain-length-hydroxyacyl-coenzyme A (3–5 carbons in length); MCL-HA-CoA (C6-C14), medium-chain-length-hydroxyacyl-coenzyme A (6–14 carbons in length); SCL-MCL-HA-CoA (C3-C14), short-chain-length-medium-chain-length-hydroxyacyl-coenzyme A (3–14 carbons in length).
b Class of PHA synthase.
c Name of PHA synthase subunit or subunits if the enzyme consists of more than PhaC.
d Native microorganism where the PHA synthase and polymer are found.
e Polymers produced. SCL-PHA, short-chain-length polyhydroxyalkanoate, MCL-PHA, medium-chain-length polyhydroxyalkanoate; SCL-MCL-PHA, short-chain-length-medium-chain-length polyhydroxyalkanoate.