Heterologous expression of the acyl–acyl carrier protein thioesterase gene from the plant Umbellularia californica mediates polyhydroxyalkanoate biosynthesis in recombinant Escherichia coli
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The acyl–acyl carrier protein (ACP) thioesterase cDNA from the plant Umbellularia californica was functionally expressed in various recombinant Escherichia coli strains in order to establish a new metabolic route toward medium-chain-length polyhydroxyalkanoate (PHAMCL) biosynthesis from non-related carbon sources. Coexpression of the PHA synthase genes from Ralstonia eutropha and Pseudomonas aeruginosa, or only the PHA synthase gene from P. aeruginosa, respectively, showed PHAMCL accumulation when the type II PHA synthase from P. aeruginosa was produced. Both wild-type E. coli and various fad mutants were investigated; and only when the β-oxidation pathway was impaired PHAMCL accumulation from gluconate was observed, contributing to about 6% of cellular dry weight. Thus coexpression of type II PHA synthase gene with cDNA encoding the medium-chain acyl-ACP thioesterase from U. californica established a new PHAMCL biosynthesis pathway, connecting fatty acid de novo biosynthesis with fatty acid β-oxidation, using a non-related carbon source.
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