Tolerance to vanadium as a response of agricultural soil fungi in the Valle Latina (Italy): which are the potentialities for mycoremediation?

The aim of this work was to investigate a soil fungal community of contaminated agricultural soils and to test the growth response of selected species to the toxic metal vanadium. Physico-chemical analysis was performed on contaminated soils that lay under maize and wheat crops in the Valle Latina (southern Lazio, Italy). The Valle Latina is one of the 57 sites of national interest (S.I.N.). It’s a high environmental risk area due to its industrial sites, waste landfills and agricultural activities and the environmental contamination of hexachlorocyclohexane, an anthropogenic pollutant. Moreover, natural background high level of potentially toxic elements due to volcanic rocks (pyroclastic deposits) occurs in this area in which several elements, including vanadium, thallium and beryllium exceed the threshold values established by Italian legislation, as well. The soil community of saprotrophic fungi of contaminated agricultural soils near the Sacco River have been studied. Contrary to expectations, the community was found to be rich in fungal species (150 species in total), although the typical Penicillium and Aspergillus species components were poorly represented. Species, reported to be tolerant/resistant to heavy metals in the literature and potentially useful in bioremediation, were found. The occurrence of these may be taken as a potential bioindicator of environmental pollution. Vanadium, one of the elements which exceed threshold values, was chosen as metal to test fungi tolerance. In the last decades, evidence in increasing of the environmental levels of vanadium, has raised concern over its release into the atmosphere from anthropogenic sources of which hydrocarbon fuel combustion is the most important. Burning of fossil fuels caused about 110000 t V/a to enter the atmosphere globally (Manfred, 2004). Vanadium is essential for several species of green algae, fungi and nitrogen-fixing microorganisms, as well. We selected six species : Aspergillus terreus Tiegh., Cladosporium cladosporioides (Fresen.) G.A. de Vries, Clonostachys rosea (Preuss) Mussat, Paecilomyces lilacinus (Thom) Samson, Penicillum citrinum Sopp and Rhizopus arrhizus Fischer, among isolated species, reported to be tolerant/resistant to heavy metals in the literature, and examined the growth response by inoculating them with malt extract agar amended with ammonium vanadate at concentrations of 1, 2, 3 and 6 mM to simulate potential environmental concentrations. Metal tolerance was assessed in all samples by means of growth measurements, tolerance index, scanning electron microscopy, electron dispersion spectroscopy and biomass metal concentrations. Results revealed that all the fungi tested tolerated 6 mM concentrations, Clonostachys rosea and Rhizopus arrhizus being the most tolerant. Soil fungi tolerance to natural metal occurrence may explain their tolerance to anthropogenic contamination. Therefore results of this research can contribute to enhance knowledge on the potential use of these fungal species for mycoremediation purposes in polluted sites.