Role of filamentous fungi in mycoremediation of soils contaminated by organic pollutants

Hexachlorocyclohexane (HCH) is a highly persistent organic pollutant of global concern, involving severe risks for human health and ecosystem functioning. Mycoremediation represents a feasible nature-based solution for the restoration of soils polluted by HCH thanks to the ability of fungi to tolerate, bioaccumulate and degrade it. Soil fungi represent promising bioresources for the bioremediation of HCH-contaminated environments. This study was conducted in the National Priority Site “Bacino del Fiume Sacco” in the Metropolitan City of Rome, Italy. Soil cores (0–100cm) were collected from two plots and divided into topsoil (TS: 0–10 cm) and subsoil (SS: 10–100cm) samples. The soil samples were characterised through pedological analysis. Microbial community-level physiological profiles were assessed using the Biolog EcoPlate™, revealing differences in metabolic activity between TS and SS communities. The fungal fraction was further investigated by quantifying colony-forming units (CFUs) per gram of dry soil. Results indicated a significantly higher fungal load in TS compared to SS. To isolate fungal strains capable of degrading HCH, a selective enrichment procedure was performed using a mixture of HCH isomers as the sole carbon source. The procedure led to the isolation of several fungal species, predominantly from Fusarium, Alternaria, and Paracremonium genera, now preserved in the Fungal Biodiversity Laboratory Culture Collection (Sapienza University of Rome). Three biosurfactant production assays demonstrated the ability of nine isolates to produce biosurfactants, potentially enhancing HCH bioavailability and degradation. Finally, a 96-wells enrichment assay was used to evaluate fungal growth responses to individual HCH isomers as sole carbon sources. Among all the species isolated, these results show that three strains isolated in this study, belonging to the Fusarium genus, are able to use the HCH-isomers as sole carbon source and to produce biosurfactants. These strains are Fusarium nirenbergiae FBL - BC 6, Fusarium nirenbergiae FBL - BC 8 and Fusarium nirenbergiae FBL - BC 56 and all came from toposil. This is the first study that reported this species as a potential candidate for mycoremediation of HCH-contaminated soil.