Metabolic responses of soil fungi to the presence of hexachlorocyclohexane isomers

Contamination represents one of the main threats to the stability and functioning of soils worldwide. The halogenated organic compound hexachlorocyclohexane (HCH), widely used as the insecticide Lindane (γ-HCH), is toxic and carcinogenic for humans and can cause severe damage to natural ecosystems in the short and long term. Due to its chemical properties, HCH can persist for a long time in soils and bioaccumulate along the food chain. Three isomers, α-HCH, β-HCH and γ-HCH, are persistent organic pollutants, included in the Stockholm Convention since 2009. Fungal bioremediation (mycoremediation) can be an environmentally friendly, feasible and cost-effective solution for HCH contamination of soils since fungi are versatile microorganisms that can adapt to extreme and heterogeneous environmental conditions of soils. They possess efficient extracellular degradative enzymes with relatively non-specific activities that can transform organic pollutants into less toxic forms or completely degrade them. The study of interactions between HCH isomers and fungal species can help to find potential candidates for soil bioremediation and better understand the biotransformation mechanisms involved. Four fungal strains, isolated from highly HCH-contaminated soils, were selected and their phenotypes compared in control and test conditions. The Biolog® Phenotype MicroarrayTM system (PM) was used to test their metabolic feedbacks in the presence of β-HCH or a mixture of HCH isomers (α-HCH, β-HCH, γ-HCH, δ-HCH) against many different carbon sources. The response of the fungi to toluene, used as a solvent to prepare the stock solutions, was also tested. Phenotypic profiles were analysed through the opm R package. Results highlight the tolerance of the selected fungal isolates to HCH isomers (β-HCH or HCH mixture) in the presence of specific carbon sources. Some Biolog substrates triggered significant differences between the strains in their metabolism at the presence of the xenobiotic compounds (toluene, β-HCH or HCH mixture), thus suggesting the activation of differential pathways.