Biosynthesis and structural characterization of polyhydroxyalkanoates produced by Pseudomonas aeruginosa ATCC 27853 from long odd-chain fatty acids

Abstract

Pseudomonas aeruginosa ATCC 27853 was cultured on media containing long odd-chain fatty acids. Heptadecanoic, nonadecanoic, and heneicosanoic acids sustained cell growth and resulted in polyhydroxyalkanoate (PHA) accumulation when culturing was conducted under nitrogen starvation conditions. No PHA was produced using a complete or magnesium-deprived medium. The isolated polyesters were characterized by gas chromatography and liquid chromatography-electrospray ionization mass spectrometry (ESI-MS) of methanolyzed samples, ¹H and ¹³C NMR spectroscopy, gel permeation chromatography, ESI MS of partially pyrolyzed samples, and differential scanning calorimetry. These PHAs are composed of seven different odd-chain repeating units starting from 3-hydroxyvalerate, with the highest species being the, to date, unreported constituent 3-hydroxyheptadecanoate, and minor amounts of 2 or 3 even-chain comonomers. The PHAs are soft, sticky, rubber-like materials having glass transition temperatures between -45 and -39°C, melting temperatures between 48 and 52°C, enthalpies of melting around 11J/g, and molar masses ranging from 77 to 188kg/mol. Statistical analysis of the ESI mass spectra of the products of their partial pyrolysis showed that they are pure copolymers and not a blend of copolymers or homopolymers.

Keywords: Copolymer sequence; ESI mass spectrometry; Fatty acids; LC-MS; NMR; Pseudomonas aeruginosa; mcl-Polyhydroxyalkanoates.