Production and characterization of medium-chain-length polyhydroxyalkanoates copolymer from Arctic psychrotrophic bacterium Pseudomonas sp. PAMC 28620

Abstract

Arctic psychrotrophic bacterium Pseudomonas sp. PAMC 28620 was found to produce a distinctive medium-chain-length polyhydroxyalkanoates (MCL-PHAs) copolymer when grown on structurally unrelated carbon sources including glycerol. The maximum MCL-PHAs copolymer yield was obtained about 52.18 ± 4.12% from 7.95 ± 0.66 g/L of biomass at 144 h of fermentation when 3% glycerol was used as sole carbon and energy source during the laboratory-scale bioreactor process. Characterization of the copolymer was carried out using fourier transform infrared spectroscopy (FTIR), gas chromatography-mass spectrometry (GC-MS), proton (1H) and carbon (13C) nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC), differential scanning calorimeter (DSC) and thermo-gravimetric analysis (TGA). The copolymer produced by Pseudomonas sp. PAMC 28620 consisting of four PHA monomers and identified as 3-hydroxyoctanoate (3HO), 3-hydroxydecanoate (3HD), 3-hydroxydodecanoate (3HDD) and 3-hydroxytetradecanoate (3HTD). An average molecular weight of the copolymer was found approximately 30.244 kDa with polydispersity index (PDI) value of 2.05. Thermal analysis showed the produced MCL-PHAs copolymer to be low-crystalline (43.73%) polymer with great thermal stability, having the thermal decomposition temperature of 230 °C to 280 °C, endothermic melting temperature (Tm) of 172.84 °C, glass transition (Tg) temperature of 3.99 °C, and apparent melting enthalpy fusion (ΔHm) about 63.85 J.g-1.