Description du sujet de thèse

The growing contamination of soils and surface water by pesticides is a major environmental and public health issue. it requires the development of effective and sustainable remediation methods. Among the approaches developed, biodegradation has proven to be an effective, natural and cheap alternative to conventional physico-chemical processes. Nevertheless, the use of microbial strains often leads to the formation of transformation products (metabolites), which can be more toxic and behave very differently from the parent molecule. Therefore, to enable such treatments to be effectively used, it is essential to understand the biodegradation mechanisms involved, to combine degrading microbial strains to achieve mineralization of the pesticide and to determine the optimal conditions for its use in environmental conditions.

The thesis subject will focus on the case of nicosulfuron, a widely used corn herbicide frequently found, as its two main metabolites (ASDM and ADMP), in water and soil, sometimes beyond the potability standards. Several degrading microbial strains have been described but most of them lead mainly to ADMP and ASDM, the latter metabolite being more toxic and more persistent than the parent herbicide. The main objective is therefore to develop an effective solution for the biodegradation of these compounds that can be used in the field.
To do this, the study will be divided into 4 main areas: (1) the immobilization of herbicide-degrading strains within porous inorganic matrices such as Lamellar Double Hydroxides (LDH) or nanocomposites based on LDH and biopolymers (alginate, chitosan, agarose); (2) the identification of enzymes potentially degrading the nicosulfuron metabolites, ASDM and ADMP; (3) the screening of biodiversity to identify efficient enzymes/microorganisms; (4) the co-immobilization of the most efficient actors within LDH/biopolymer nanocomposites and the study of their biodegradation performance once immobilized.
This study will provide solid foundations for the development of an original optimization strategy in the context of bioremediation adapted to contaminated soils and waters, which could be extended to other pesticides.

At the interface between environmental microbiology, biocatalysis and materials chemistry, this study will bring together essential multidisciplinary expertise from two teams at the Clermont-Ferrand Institute of Chemistry (ICCF) and will draw on a collaboration with Génoscope (Evry).

The thesis, funded by the International MITI from CNRS, is part of the broader framework of an International Associated Laboratory of Environmental Processes and Remediation (LPRE) between the University of Clermont Auvergne, the CNRS, and Wuhan University (China). This laboratory is dedicated to improving environmental quality (water, air, soil) and recognized as an IRP (International Research Project) by the CNRS for 5 years (2022–2026).

Contexte de travail

-- The student recruited will be attached to the Clermont-Ferrand Institute of Chemistry (UMR CNRS 6296) on the science Campus. The laboratory comprises approximately 300 people, over a third of whom are permanent staff. It is organized around six research teams covering the various chemistry fields (organic and medicinal, bio-organic, inorganic and physical).

The doctoral student will work in the "Biocatalysis and Metabolism" (BioMETA) and "Materials" (MI) teams of the ICCF and will interact with the Génoscope.

- Co-supervision: Pascale Besse-Hoggan (CNRS Research Director, BioMETA Team), Vanessa Prévot (CNRS Research Director, MI Team) and Christine Hélaine (MCF, BioMETA Team).

Contraintes et risques

Risks inherent to laboratory work