Print PageLead (Pb) contaminated soils represent severe environmental problems as well as a significant hazard to human health. Prolonged exposure to high levels of toxic metals exerts considerable selective pressure on the soil microbial community and alters soil and ecosystem health. Many species of fungi are capable of transforming insoluble metal compounds into soluble derivatives, an environmentally important process when these fungi constitute a significant portion of the overall soil community. The objective of this study is to understand how Pb contamination at an abandoned small-arms firing range in east Tennessee has affected the soil fungal community structure and the potential capacity of the soil fungal community for Pb-mineral solubilization via organic acid secretion.
Six soils were collected from locations around the abandoned firing range and were analyzed for total Pb content. These soils were subsequently used to derive fungal isolates via serial dilution plating. Isolates were screened for organic acid production via pH indicators in the growth media as well as HPLC analysis. Isolates were also screened for solubilization of lead carbonate and pyromorphite at concentrations ranging from 3mM to 18mM. Phylogenetic identification of isolates were derived from sequencing of the ITS and/or 28S rRNA genes.
Results/Conclusions
Soil Pb concentrations ranged from 23.6 mg kg-1 to over 2500 mg kg-1 and the number of cultivable fungi was not significantly different between soil Pb levels. We obtained 220 total isolates, 26% of which were capable of acidification of two different types of growth media. Of those 58 isolates, sequencing and phylogenetic comparisons suggest approximately 22 species groups are represented. These include both ascomycetes and basidiomycetes with Eupenicillium and Phanaerochaete being the prominent genera. Types and amounts of organic acids secreted varied with phylogenetic affiliation and several of these species were also capable of solubilizing lead carbonate at all tested concentrations.
Most of the cultivable fungi in this study were capable of acidifying their growth media and we were able to identify several organic acids secreted in liquid media as well. This could likely mean these fungi are capable of acidification of their native soil habitats. Many of these acid-producing fungi were also capable of solubilizing lead-carbonate, a Pb-mineral frequently found at both active and abandoned firing ranges. We are currently performing a pyrosequencing-based analysis of the overall soil fungal communities from which these isolates derived to shed light on the importance of these species in contaminated soil systems.
