Microbial Degradation of Polyester Based Biodegradable Plastics

Abstract

The present study was aimed to isolate and characterize microorganisms capable of degrading polyester-based biodegradable plastics under natural soil conditions. Two fungi, designated as strain SS2 and S45, were isolated from soil that could degrade various polyesters of natural as well as synthetic origin, both in emulsion as well as film form. Strain SS2 and S45 were identified through 18S rRNA gene sequencing and found closely similar to Penicillium sp. and Aspergillus sp., having 100 and 99% similarity with Penicillium oxalicum and Aspergillus fumigatus, respectively. P. oxalicum SS2 could efficiently degrade polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate (PHBV) emulsion as well as films in liquid medium within 36-48 hrs. The fungus showed maximum growth and degradation at 30°C that represented its mesophilic nature. Furthermore, the role of P. oxalicum SS2 in degradation of polyester films in soil environment was evaluated by soil burial experiment in lab-built microcosms where the fungus degraded PHB and PHBV films in 7 days. Aspergillus fumigatus strain S45 showed degradation potential against poly(caprolactone) (PCL) and polyurethane (PU). Bio-augmentation of the fungus in soil accelerated biodegradation of PCL film. While measurement of weight loss and evolution of CO2 showed breakdown of PU film upon inoculation with S45. The biodegradation of polyesters was further confirmed through various qualitative assays such as scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and fourier transform infrared (FTIR) spectroscopy. Aspergillus fumigatus strain S45 was found to show esterase activity during biodegradation of PU. This study demonstrated soil as a reservoir for polyester-degrading microorganisms which could be utilized for the development of novel waste management strategies.