Carbonaceous nanomaterials stimulate extracellular enzyme release by the fungus Cladosporium sp. and enhance extracellular electron transfer to facilitate lignin biodegradation

The release of carbonaceous nanomaterials (CNMs) into the environment inevitably affects the surrounding microenvironment, biochemical processes of microbes, and even entire ecosystems. However, the knowledge of the impact of CNMs on the environmental microbial activities and further natural organic matter biodegradation is still less known. Here we investigated the impact of three CNMs (single-walled carbon nanotubes, graphene, and oxidized graphene) on extracellular enzymes activities of a fungal strain (Cladosporium sp.) and lignin biodegradation. All three CNMs increased the activities of three non-specific enzymes (laccase, manganese peroxidase, and lignin peroxidase) to different degrees, among which manganese peroxidase activity increased significantly, with an average promotion of 20% within 18 days. Meanwhile, structural characterization revealed the transformations of CNMs caused by fungal biodegradation. CNMs stimulation fungal enzyme activities further enhanced lignin degradation. Adsorption experiments and electrochemistry analysis demonstrated the mechanism that CNMs acted as adsorbent of extracellular enzymes as well as electron conductors, which enhanced extracellular direct electron transfer between enzymes and lignin and facilitated lignin conversion and degradation. Our results highlight the potential effect of CNMs on the lignin degradation by fungi, and require consideration when evaluating the environmental effects of CNMs on microbial communities or even carbon cycling across whole ecosystems. (C) 2019 Elsevier B.V. All rights reserved.