Recombinant Escherichia coli strains defective in FadA and/or FadB harboring the Pseudomonas sp. 61-3 polyhydroxyalkanoate (PHA) synthase gene (phaC2(Ps)) were constructed, and were examined for the production of medium-chain-length (MCL) PHA from sodium decanoate and sodium dodecanoate. All the recombinant E. coli strains accumulated MCL-PHAs mainly composed of C6, C8 and C10 monomers from decanoate and those composed of C8, C10 and C12 monomers from dodecanoate. A new metabolic engineering strategy for enriching specific monomers in MCL-PHA was developed by examining the effect of co-expressing the E. coli fadD(Ec), fad(Ec), and/or fadL(Ec) genes along with the PHA synthase gene. Using these engineered E coli strains, MCL-PHAs enriched in 3-hydroxydecanoate up to 80 mol% and 3-hydroxydodecanoate up to 48 mol% were produced from sodium decanoate and sodium dodecanoate, respectively. It was found that the amplification of the fadD(Ec), fadE(Ec) or fadL(Ec) gene had different effect on the monomer composition of MCL-PHA. Among these, the amplification of the fadD(Ec) gene had the most significant effect on the alteration of monomer composition of MCL-PHAs. (C) 2003 Elsevier Science Inc. All rights reserved.