Bacterial degradation and environmental impact of carbon nanotubes – DECANO

Carbon nanotubes (CNTs) represent an emerging nanomaterial for a wide range of applications both in materials science and biomedicine. The increasing production of CNTs, their processing and eventual incorporation into new types of composites and/or into biological systems has raised fundamental issues on the impact of CNTs on health and environment. In the context of studies on the environmental release of CNTs, accumulation and degradation of CNTs are very limited. Potential exposure routes are multiple. Depending on the life cycles of the products and their fate, CNTs may cause different environmental health effects. Indeed, the CNTs can reach the environment and eventually accumulate along the food chain. The study of the destiny of the types of CNTs released in the environment is important to avoid possible risks of contamination, pollution and damages to the living systems. As CNTs will be disseminated in the environment at some concentration, terrestrial and aquatic microorganisms coming in contact with the CNTs will integrate such materials and eventually try to eliminate using their metabolic capacities of degradation.
In this context, the main objective of the DECANO project is to study the interactions between functionalized CNTs and bacteria. We will explore the possibility that these bacteria, possessing high enzymatic activities (i.e. oxidative action), could carry out the degradation of CNTs. Recent studies by the group of Star showed the capacity of peroxidases to degrade CNTs in the presence of low concentrations of hydrogen peroxide. We will perform in silico studies to identify new oxidative enzymes into the available genomic and metagenomic data banks capable of degrading CNTs. We will also assess the potential toxicity of products arising from the degradation of CNTs. Pristine CNTs are extremely difficult to manipulate due to solubilization/dispersibility problems and manufactured products often incorporate nanotubes that have been previously modified. As a consequence, we have chosen to study functionalized CNTs rather than pristine material. Thus, carboxylated double- and multi-walled carbon nanotubes and further modified CNTs will be investigated in DECANO for the identification and selection of enzymes capable of biodegradation. We will identify the fragments derived from the degradation of CNTs and their potential use as carbon source by bacteria. For this purpose, 13C-labeled CNTs will be used and 13C-enriched biomolecules potentially integrated into the microorganisms will be identified. In parallel, we will analyze the impact of CNTs and their biodegradation products on the bacterial populations and the ecotoxicity on an amphibian model. The ultimate goal of the DECANO project is the development of bioremediation processes of CNTs involving naturally occurring bacterial systems. It is highly important as the production of CNTs and the integration of CNTs in products available on the market are exponentially growing, along with the risk of contamination of the environment with CNTs. The results gathered in the DECANO project could lead to a natural route to reduce the potential contamination risk of CNTs in the environment.