Properties of engineered poly-3-hydroxyalkanoates produced in recombinant Escherichia coli strains

To prepare medium-chain-length poly-3-hydroxyalkanoates (PHAs) with altered physical properties, we generated recombinant Escherichia coli strains tha t synthesized PHAs,with altered monomer compositions. Experiments with diff erent substrates (fatty acids with different chain lengths) or different E. coli hosts failed to produce PHAs with altered physical properties. Theref ore, we engineered a new potential PHA synthetic pathway, in which ketoacyl -coenzyme A (CoA) intermediates derived from the alpha-oxidation cycle are accumulated and led to the PHA polymerase precursor R-3-hydroxyalkanoates i n E. coli bests. By introducing the poly-3-hydrolybutylate acetoacetyl-CoA reductase (PhbB) from Ralstonia eutropha and blocking the ketoacyl-CoA degr adation step of the beta-oxidation, the ketoacyl-CoA intermediate was accum ulated and reduced to the PHA precursor. Introduction of the phbB gene not only caused significant changes in the monomer composition but also caused changes of the physical properties of the PHA, such as increase of polymer size and loss of the melting point. The present study demonstrates that pat hway engineering can be a useful approach for producing PHAs with engineere d physical properties.