Microbial Synthesis of Poly(3-hydroxyalkanoates) by Pseudomonas aeruginosa from Fatty Acids: Identification of Higher Monomer Units and Structural Characterization

Pseudomonas aeruginosa ATCC 27853 accumulated poly(3-hydroxyalkanoates) (PHAs) after growth on satd. fatty acids with an odd no. of carbon atoms. No nutrient limitation was required to induce PHA synthesis, although better yields were obtained when the medium was magnesium deprived. A comparative study was carried out between PHAs obtained from C-odd and those from C-even carbon sources. Repeating units identification was performed by gas chromatog. (GC) and capillary liq. chromatog.-electrospray mass spectrometry (LC-ESI MS) of methanolyzed samples. When C-odd n-alkanoic acids from nonanoic to pentadecanoic were used the lowest hydroxyalkanoate unit found was 3-hydroxyvalerate and the highest 3-hydroxypentadecanoate, whereas when C-even acids from octanoic to eicosanoic were used these were 3-hydroxycaproate and 3-hydroxyeicosanoate, resp. Wt. av. mol. wts. were in the range 187,000-596,000. DSC traces showed Tm and DHm which varied from 43 to 58 °C and from 5.9 to 24.8 J/g, with the PHAs generated from C-odd carbon sources having lower values. ESI MS of partially pyrolyzed samples allowed the identification of oligomers up to heptamers, and statistical anal. of the ions intensity in the mass spectra showed that these PHAs are random copolyesters.