Isolation and characterisation of fungal communities associated with degradation and growth on the surface of poly(lactic) acid (PLA) in soil and compost

Abstract

Polylactic acid (PLA) is a compostable biopolymer that is currently used for short shelf-life product containers and waste disposal bags. At temperatures at or above its glass transition temperature (55°–62 °C), PLA in the presence of water undergoes chemical hydrolysis, progressively reducing polymer molecular weight and ultimately releasing lactic acid. The role of microorganisms in this process has largely focused on bacteria, with few studies investigating potential role of fungi. In this study, PLA (96% l-isomer) coupons were buried in soil or compost and incubated at 25 °C or 50 °C for up to 8 weeks. Physical disintegration of the coupons was seen only when incubated at 50 °C in both soil and compost. The principle fungal species identified from PLA coupons at 25 °C included Mortierella sp., Doratomyces microsporus, Fusarium solani, Fennellomyces sp., Aspergillus fumigatus, Verticillium sp., Lecanicillium saksenae, Cladosporium sp. and Trichoderma sp. Only Thermomyces lanuginosus and A. fumigatus were isolated from PLA at 50 °C and both were shown to cause significant PLA biodegradation as determined by tensile strength loss compared to abiotic controls. Terminal restriction fragment length polymorphism (TRFLP) demonstrated strong selection of specific fungal species from soil and compost communities on PLA the surface and a greater species diversity than could be detected by conventional culturing techniques.