Biosynthesis of medium chain length poly-3-hydroxyalkanoates by Pseudomonas guezennei from various carbon sources

Abstract

The biosynthesis of poly-(3-hydroxyalkanoates) (PHAs) by Pseudomonas guezennei using glucose and/or fatty acids with chain-length from 3 to 18 carbon atoms as carbon sources was investigated. Glucose, acetate, pyruvate, propionate, valerate, hexanoate, heptanoate, octanoate, decanoate, and oleic acid were supplemented in the mineral medium as the sole carbon source or as a mixture for PHAs accumulation. Chemical composition of the resulting PHAs was analysed by coupled gas chromatography mass spectroscopy (GCMS), Fourier Transform Infrared Spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). PHAs contained up to 10 different types of 3-hydroxyalkanoic acid units, including saturated 3-hydroxyacids from C4 to C14, and unsaturated monomers as 3-hydroxydodecenoate (3HDde) and 3-hydroxytetradecenoate (3HTde). 3-Hydroxydecanaote (3HD) and 3-hydroxyoctanaote (3HO) were incorporated preferentially except during cultivation on heptanoic acid, when P. guezennei synthesized PHAs with a higher concentration of 3-hydroxyheptanoate (3HHp). Thermal analysis indicated semi-crystalline polymers with melting temperatures ( T m) ranging from 42 and 51 °C, fusion enthalpy (Δ H m) comprised between 4 and 22 J/g, and glass transition temperatures ( T g) from −41 to −50 °C. Crystallinity index (CI) as deduced from FTIR spectra showed values comprised between 0.32 and 0.37. Molecular weights as determined by gel permeation chromatography (GPC-MALLS) ranged from 64 200 to 390 000 g/mol. The results obtained from this study indicate that P. guezennei is capable of producing a variety of medium chain length (MCL) PHAs via de novo fatty acid biosynthesis and β-oxidation depending on the nature of the carbon source supplied.