Heterologous expression of the acyl-acyl carrier protein thioesterase genefrom the plant Umbellularia californica mediates polyhydroxyalkanoate biosynthesis in recombinant Escherichia coli

The acyl-acyl carrier protein (ACP) thioesterase cDNA from the plant Umbell ularia californica was functionally expressed in various recombinant Escher ichia coli strains in order to establish a new metabolic route toward mediu m-chain-length polyhydroxyalkanoate (PHA(MCL)) biosynthesis from non-relate d carbon sources. Coexpression of the PI-IA synthase genes from Ralstonia e utropha and Pseudomonas aeruginosa, or only the PHA synthase gene from P. a eruginosa, respectively, showed PHA(MCL) accumulation when the type II PHA synthase from P. aeruginosa was produced. Both wild-type E, coli and Variou s fad mutants were investigated; and only when the beta -oxidation pathway was impaired PHA(MCL) accumulation from gluconate was observed, contributin g to about 6% of cellular dry weight. Thus coexpression of type II PHA synt hase gene with cDNA encoding the medium-chain acyl-ACP thioesterase from U, californica established a new PHA(MCL) biosynthesis pathway, connecting fa tty acid de novo biosynthesis with fatty acid beta -oxidation, using a non- related carbon source.