Oxidative biodegradation of single-walled carbon nanotubes by partially purified lignin peroxidase from Sparassis latifolia mushroom

Two types of carbon nanotubes (usually single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs)) have been intensively focused on academic researches and mass-produced for wide applications such as composite materials, biosensors, and drug delivery systems. However, due to oxidative stress-dependent and physically-induced cellular toxicity of CNTs, many efforts to render biocompatible and biodegradable properties in CNTs have been highlighted. Thus, taking into the consideration of exposure in human health and the environment, biodegradation of CNTs as a potential disposal is highly addressed. In this study, lignin peroxidase (LiP) was isolated and partially purified from the fruiting bodies of the edible mushroom Sparassis latifolia (S. latifolia). The biodegradation of raw grade and thermally-treated carboxylated SWCNTs (denoted as ASA and AST) with this enzyme was investigated, prior to more biodegradation-resistant MWCNTs. The interactions between the SWCNTs and LiP were investigated using various techniques, and the intermediate by-products of the LiP degradation were identified. Our findings demonstrated that both ASA and AST were efficiently degraded by LiP where the producing radicals by the LiP played a critical role in the biodegradation of SWCNTs. The final degraded products were confirmed with the generation of CO2 gas. Conclusively, the low extraction cost of partially purified enzyme from mushrooms can make this approach a promising alternative in environmental bioremediation as a practical application.