The Halophilic Bacterium Paracoccus haeundaensis for the Production of Poly(3-Hydroxybutyrate-co-3-Hydroxyvalerate)...

The study objective was to evaluate the potential production of polyhydroxyalkanoates (PHAs), a biodegradable plastic material, by Paracoccus haeundaensis for which PHA production has never been reported. To identify the most effective nitrogen-limited culture conditions for PHAs production from this bacterium, batch fermentation using glucose concentrations ranging from 4 g l^-1 to 20 g l^-1 with a fixed ammonium concentration of 0.5 g l^-1 was carried out at 30°C and pH 8.0. A glucose supplement of 12 g l^-1 produced the highest PHA concentration (1.6 g l^-1) and PHA content (0.63 g g^-1) thereby identifying the optimal condition for PHA production from this bacterium. Gas chromatography-mass spectrometry analysis suggests that P. haeundaensis mostly produced copolymer types of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] from glucose concentrations at 12 g l^-1 or higher under the nitrogen-limited conditions. When several other single carbon sources were evaluated for the most efficient PHA production, fructose provided the highest biomass (2.8 g l^-1), and PHAs (1.29 g l^-1) concentrations. Results indicated that this bacterium mostly produced the copolymers P(3HB-co-3HV) from single carbon sources composing a range of 93-98% of 3-hydroxybutyrate and 2-7% of 3-hydroxyvalerate, whereas mannose-supplemented conditions produced the only homopolymer type of P(3HB). However, when propionic acid as a secondary carbon source were supplemented into the media, P. haeundaensis produced the copolymer P(3HB-co-3HV), composed of a 50% maximum monomeric unit of 3-hydroxyvaleric acid (3HV). However, as the concentration of propionic acid increased, cell biomass and PHAs concentrations substantially decreased due to cell toxicity.