Submitted to: Applied Microbiology and Biotechnology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/7/2009
Publication Date: 11/1/2009
Citation: Ashby, R.D., Ngo, H., Solaiman, D., Strahan, G.D. 2009. Methyl-branched poly(hydroxyalkanoate) biosynthesis from 13- methyltetradecanoic acid and mixed isostearic acid isomer substrates. Applied Microbiology and Biotechnology. 85:359-370. Interpretive Summary: Over the past decade or so environmental concern has moved to the forefront as an issue that needs to be resolved in order to maintain current living standards. As such, many industries are focusing on “green” technologies (technologies that leave a minimal environmental footprint) by converting many established products and processes to more benign formulations. Poly(hydroxyalkanoates) (PHAs) are bio-based polyesters that are produced by many different bacterial strains under defined growth conditions. These PHAs, which have been shown to be completely biodegradable in landfill as well as aquatic environments, are currently receiving interest as substitutes for many of the nonbiodegradable, petrochemical-based materials, such as polyethylene and polypropylene. One of the limiting factors in the widespread use of these bio-based PHAs is the ability to control their properties. In this study we used a recently developed technology to produce chemically-branched oils and subsequently used these materials as feedstocks for the production of new biodegradable PHAs with unique structural properties. The success documented in this work has further broadened the library of potential PHA-types and may further aid in the synthesis of new “environmentally friendly” materials with select properties.
Technical Abstract: Pseudomonas resinovorans, a known medium-chain-length (mcl-) poly(hydroxyalkanoate) (PHA) producer, was grown on 13-methyltetradecanoic acid (13-MTDA) and a mixture of isostearic acid (IA) isomers to produce methyl-branched mcl-PHA polymers. Shake flask experiments revealed polymer productivities (the percent of the cell mass that is polymer) of 31 +/- 1% (n=3) and 23 +/- 3% (n=3) when grown in 13-MTDA and IA, respectively. Monomer content was determined by gas chromatography / mass spectrometry (GC/MS) of the acid hydrolyzed, silylated methyl esters. Results showed that the mcl-PHA polymer derived from 13-MTDA was primarily composed of 3-hydroxy-7-methyloctanoic acid (67 mol%) and 3-hydroxy-9-methyldecanoic acid (16 mol%). In contrast, the mcl-polymers synthesized from the IA isomeric mixture were more complex, containing both even and odd chain-length monomers as well as varying distributions of methyl-branched derivatives. The PHA distributions among the C8, C10, C12 and C14 carbon chain-length monomers included 3 isomers of C8, 5 isomers of C10, 7 isomers of C12 and 9 isomers of C14 each containing one linear-chain derivative and n-6 methyl-branched derivatives where n equals the total number of carbon atoms in each monomer unit (C8-C14).