Recyling Poly-3-hydroxybutyrate

Poly-3-hydroxybutyrate(P3HB) is a bioplastic, more specifically it is a polyester which is naturally produced inside bacteria such as Alcaligenes eutrophus. It is used as an energy store by these bacteria(1). It appears as globules inside the cell. PHB as a plastic has benefits over those derived from oils; it is produced from renewable resources which minimise the amount of fossil fuels required in plastic production(2,3) and can also biodegrade to non-toxic compounds which can be used as an energy source by organisms commonly found in the environment(4). Physically P3HB has properties which allow it to be used as a replacement for oil based plastics for some application e.g packaging(5) such as .

We have made P3HB in E.coli and developed a system by which it can be recycled when products made from it come to the end of their life. In order to make P3HB we transferred three genes, naturally found in Ralstonia eutropha into E.coli MG1655. These encode the three enzymes necessary for P3HB production; polyhydroxyalkanoate synthase(phaC), 3-ketothiolase(phaA) and acetoacetyl coenzyme A reductase(phaB). These exist as a P3HB producing operon. We have tried to genetically maximise the production of P3HB as high yields are required for P3HB to be economically viable.

phaC, which encodes the polyhydroxyalkanoate (PHA) synthase, phaA, which encodes a 3-ketothiolase, and phaB, which encodes an acetoacetyl coenzyme A (acetoacetyl-CoA) reductase.