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Chlordecone degradation and Desulfovibrio sp. 86: Dr Jekyll or Mr Hyde?

In a study published in Scientific Reports and following upon their unprecedented isolation and sequencing of a bacterium capable of degrading chlordecone, one of the most ecotoxic pesticides to have ever existed, researchers from the Genomics Metabolics lab (Genoscope/CEA-Jacob) have shown that a same bacterial species can break down chlordecone differently according to the conditions in which it was cultivated. Furthermore, one of the newly-discovered sulfur-containing degradation products was detected in a chlordecone-contaminated French Antillean mangrove, demonstrating the environmental importance of the results.

Published on 11 August 2020

Chlordecone (C10Cl10O2H2) was widely used in the French West Indies between 1972 and 1993 as an insecticide against banana weevils. It was classified as a persistent organic pollutant in 2001 and is now prohibited, but because of its persistence and its bioconcentration in the food chain, human contamination remains widespread in the local populations. The chronic pollution and toxicity of the compound causes serious socioeconomic and public health issues.

For about ten years now, a team from the Genomics Metabolics mixed research unit at Genoscope has been using bacteria in anaerobiosis (oxygen-free atmosphere) to study chlordecone biodegradation. The team has identified a consortium of bacteria able to break down chlordecone in previously-published works1,2 and isolated some of them, including one in the Citrobacter genus. The three large families of transformation products identified to date appear simultaneously during microbiological degradation.

In a new study published in Scientific Reports, the researchers isolated and studied a new bacterium, Desulfovibrio sp. 86. They reported that according to culturing conditions, this bacterium can generate either the three families of transformation products mentioned above, or novel transformation products. In various experiments, the team determined the critical parameters needed to push the bacterium to one or the other mode of transformation and identified the presence of a sulfur atom in the novel transformation products, thus defining a fourth transformation product family. The detection of the principal sulfur-containing transformation product in several Antillean environmental samples and the over-representation of Desulfovibrio sp. 86-like bacteria signaled that this transformation mode was also occurring in certain West Indies environmental compartments.

These new results add to current laboratory knowledge on chlordecone biodegradability and enlarge the number of degradation pathways active in the West Indies. Unprecedentedly, this study showed the conversion of a ketone into a thiol by a bacterium (formerly accomplished only in organic chemistry). That discovery opens new doors to applications tied to the chemical properties of obtained compounds.


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