Isolation of fungal isolates from french west indies soil contaminated with chlordecone: evidence for chlordecone tolerance and potential biodegrading ability

Chlordecone (CLD), an organochloride insecticide used in French West Indies to control the banana weevil Cosmopolites sorditus, contaminates soils of banana plantations and water resources posing major environmental problem. Recently the link between CLD exposure and rate of prostate cancer was established (Multigner et al., 2010) highlighting a major public health concern. Being listed by the Stockholm convention as a persistent organic pollutant (POP), CLD is well known for its recalcitrance to biodegradation. Combined with a high soil organic matter, CLD is adsorbed to soils where Cabidoche et al. (2009) estimate that it will persist for several hundreds of years. Reports of CLD biodegradation being scarce, the aim of this work is to search for evidence for microbial transformation of this insecticide in West French Indies contaminated soils. The work consisted in performing enrichment cultures to isolate, characterize and test the tolerance of microorganisms from contaminated soils to CLD. Continuous culture enrichments carried out with activated charcoal (microbial communities’ sequestration) were conducted for several months on an Andosol heavily contaminated with CLD (i.e. 35 mg.kg-1). Starting from enriched soil and activated charcoal, successive enrichments were conducted in mineral salt medium added with CLD as sole carbon source in order to select CLD tolerant and/or degrading-microorganisms. Using this procedure, an important fungal diversity was retrieved from the Andosol. In total of 102 isolates gathered in 17 morphotypes were isolated. The intergenic region (ITS) between 18S and 28S genes of ribosomal operon of several representatives were sequenced. Three morphotypes namely Fusarium oxysporum (33 isolates), morphotype 1 yet unidentified (20) and Aspergillus flavus (13) co-dominate the cultivable fungal community. Fungal isolates are not known as degrading chlorinated compounds. Tolerance tests on glucose minimal medium supplemented or not with CLD have been performed on a representative of each dominant morphotype (i.e. Fusarium oxysporum strain CHL53, morphotype1 strain CHL22, Aspergillus flavus strain CHL48) and a reference strain which has never been in contact with CLD (Fusarium oxysporum MIAE00047). No statistically significant effect of CLD has been observed on the growth rate of the reference strain and isolate CHL48 (p<0.01, n=5). However, CLD increased significantly the growth rate of isolates CHL53 and CHL48 (p<0.01, n=5). These results indicate that on one hand, the tested strains are not sensitive to the CLD, and on the other hand, two isolates seem to grow on CLD. Growth tests of the three isolates and the reference strain were performed on minimal medium with CLD as the sole carbon source. Isolates CHL22, CHL48 and the reference strain did not grow, indicating that they cannot use CLD as carbon source. In contrast, strain CHL53 (F. oxysporum) grew on such a medium. These results corroborate the tolerance tests, suggesting that CHL53 is able use CLD for its growth. Radiorespirometry experiment performed with uniformly labeled 14C and GC-MS analyses of F. oxysporum CHL53 cultures are on going to evidence for CLD transformation.