Bioremediation of Dichlorodiphenyltrichloroethane (DDT)-Contaminated Agricultural Soils: Potential of Two Autochthonous Saprotrophic Fungal Strains

IMPORTANCE The spread and environmental accumulation of DDT over the years represent not only a threat to human health and ecological security but also a major challenge because of the complex chemical processes and technologies required for remediation. Saprotrophic fungi, isolated from contaminated sites, hold promise for their bioremediation potential toward toxic organic compounds, since they might provide an environment-friendly solution to contamination. Once we verified the high tolerance of autochthonous fungal strains to high concentrations of DDT, we showed how fungi from different phyla demonstrate a high metabolic versatility in the presence of DDT. The isolates showed the singular ability to keep their functionality, despite the DDT-induced production of reactive oxygen species.

DDT (dichlorodiphenyltrichloroethane) was used worldwide as an organochlorine insecticide to control agricultural pests and vectors of several insect-borne human diseases. It was banned in most industrialized countries; however, due to its persistence in the environment, DDT residues remain in environmental compartments, becoming long-term sources of exposure. To identify and select fungal species suitable for bioremediation of DDT-contaminated sites, soil samples were collected from DDT-contaminated agricultural soils in Poland, and 38 fungal taxa among 18 genera were isolated. Two of them, Trichoderma hamatum FBL 587 and Rhizopus arrhizus FBL 578, were tested for tolerance in the presence of 1-mg liter(-1) DDT concentration by using two indices based on fungal growth rate and biomass production (the tolerance indices Rt:Rc and TI), showing a clear tolerance to DDT. The two selected strains were studied to evaluate catabolic versatility on 95 carbon sources with or without DDT by using the Phenotype MicroArray system and to investigate the induced oxidative stress responses. The two strains were able to use most of the substrates provided, resulting in both high metabolic versatility and ecological functionality in the use of carbon sources, despite the presence of DDT. The activation of specific metabolic responses with species-dependent antioxidant enzymes to cope with the induced chemical stress has been hypothesized, since the presence of DDT promoted a higher formation of reactive oxygen species in fungal cells than the controls. The tested fungi represent attractive potential candidates for bioremediation of DDT-contaminated soil and are worthy of further investigations.