Enzymatic degradation of poly(hydroxyalkanoate) by Corynebacterium aquaticum IM-1 isolated from activated sludge

Abstract

Poly(4-hydroxybutyric acid)-degrading bacteria were isolated from activated sludge. One strain was selected, which was identified as Corynebacterium aquaticum. The strain C. aquaticum IM-1 excreted an extracellular poly(hydroxyalkanoate) [PHA]depolymerase and grew on 4-hydroxybutyric acid as the sole carbon source. The PHA depolymerase was purified from the cultured broth medium containing 4-hydroxybutyric acid as the sole carbon source by ultrafiltration, gel filtration and hydrophobic column chromatography. The molecular weight of the depolymerase was determined as approximately 33000 Da by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The optimum activity of the depolymerase on the degradation of poly(4-hydroxybutyrate) (P(4HB)) was observed at pH 6.5 and 40 °C. Lipase activity of the depolymerase was not detected, and N-terminal sequences of the depolymerase were not applicable to the well-known enzymes. The enzymatic degradation of polyesters was studied by the erosion rate of solution-cast films of poly(3-hydroxybutyrate- co-4-hydroxybutyrate) and poly(ω-hydroxyalkanoate) of different chain lengths (C3–C6). The water-soluble products of poly(3-hydroxybutyrate co-97mol%4-hydroxybutyrate) film were revealed by 1H NMR and FAB-MS analysis, and the main product was the dimer of 4-hydroxybutyric acid.