Biodegradation of Poly(3-hydroxybutyrate) and Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) by Newly Isolated Penicillium oxalicum SS2 in Soil Microcosms and Partial Characterization of Extracellular Depolymerase.

A fungus, designated as strain SS2 able to degrade aliphatic polyesters, poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), was isolated from soil. Strain SS2 was identified through rDNA gene sequencing and showed maximum closeness to Penicillium oxalicum. The newly isolated P. oxalicum strain SS2 had completely degraded PHB and PHBV both in emulsion and films form within 36-48 h at 30 °C. Furthermore, P. oxalicum SS2 degraded PHB and PHBV films in soil environment in lab-built soil microcosms within 1 week. The polymer films were evaluated for changes after degradation through scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC) and Fourier Transform Infrared spectroscopy (FTIR). The PHBV depolymerase enzyme was purified to homogeneity through column chromatography and molecular mass was found approximately 36 kDa. The depolymerase was stable over a wide range of temperature (15-60 °C) and pH (3.0-8.0) with optimum 40 °C and pH 5.0. The enzyme activity was significantly affected by various metal ions and surfactants. The enzyme activity was strongly enhanced in the presence of divalent cationic metal Cu2+ while inhibited by Zn2+ and non-polar detergents Tween 20 and Tween 60. Finally, it is concluded that P. oxalicum strain SS2 has profound degradation capabilities, and can be applied for the treatment of plastic-contaminated environments.