Optimization of medium composition for 3-hydroxycarboxylic acid production by Pseudomonas mendocina-biodegraded polyhydroxybutyrate.

We optimized the culture medium for 3-hydroxycarboxylic acid production by Pseudomonas mendocina DS-04-T-biodegraded polyhydroxybutyrate (PHB) using the Plackett-Burman design, steepest ascent method, and Box-Behnken design. The optimized concentrations of the constituents of the culture medium were as follows: PHB (7.57 g/L), NH4 Cl (5.0 g/L), KH2 PO4 (2.64 g/L), Na2 HPO4 ·12H2 O (12 g/L), MgSO4 ·7H2 O (0.5 g/L), and CaCl2 ·2H2 O (5 mg/L). The yield of 3-hydroxycarboxylic acid obtained using the optimized culture medium was 56.8 ± 1.64%, which was 2.5-fold higher than that obtained when the unoptimized culture medium was used.

Purification and characterization of an extracellular poly(3-hydroxybutyrate-co-3-hydroxyvalerate) depolymerase from Acidovorax sp. HB01.

The poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)-degrading strain Acidovorax sp. HB01 was isolated from an activated sludge sample. A novel PHBV depolymerase with a molecular weight of 43.4 kDa was purified to homogeneity from the culture supernatant of the HB01 strain. The optimum pH and temperature of the PHBV depolymerase were 7.0 and 50 °C, respectively. The PHBV depolymerase can also degrade polyhydroxybutyrate, poly (3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(caprolactone); however, the PHBV degradation activity of the depolymerase is higher than its activity against the other polymers. Effect of metal ions and various inhibitors on the PHBV depolymerase activity was examined. The addition of Na(+), K(+), and Ca(2+) markedly increased the hydrolysis rate, whereas the enzyme activity was inhibited by Zn(2+), Mg(2+), Mn(2+), and particularly by Cu(2+) and Fe(2+). Ethylenediaminetetraacetic acid was found to have a significant inhibitory effect. The main degradation product of depolymerase was identified as the 3-hydroxybutyric acid monomer and 3-hydroxyvaleric acid monomers via mass spectrometry.