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Abstract
Metal localisation was investigated in the lichenised ascomycete Trapelia involuta growing on a range of uraniferous minerals including metazeunerite [Cu(UO2)2(AsO4)2·8H2O], metatorbernite [Cu(UO2)2(PO4)2·8H2O], autunite [Ca(UO2)2(PO4)2·10H2O] and uranium-enriched iron oxide and hydroxide minerals at the abandoned South Terras mine site, Cornwall, UK. Apothecia from samples collected from waste dumps at the mine have an unusually dark colour that decolorized with NaOCl, an observation which together with Fourier Transform Infrared Spectroscopy of apothecial extracts, suggested the presence of melanin-like pigments. X-ray element mapping and probe traverses across the lichen-rock interface identify the highest U, Fe, and Cu concentrations in the outer parts of melanised apothecia. Accumulation of mineral particulates and complexing with lichen acids are not considered responsible for this since element ratios in the traverses do not correspond with those of likely mineral phases and lichen metabolites are localised in different tissues. Metal biosorption by melanin-like pigments are likely to be responsible for the observed metal fixation. No detectable U or Cu was observed in control samples although Fe showed a similar localisation in some specimens. The high concentrations of mucopolysaccharides and P recorded inside apothecia (within asci containing reproductive spores and hypothecium) suggests that the formation of melanised tissues may help protect vital reproductive tissues from the toxic effects of U and other metals, since the uranyl ion complexes strongly with phosphate species.
We are grateful to English Nature and Boconnoc Estates for allowing access and sampling at the South Terras site. We thank A. Ball, J. Francis, G. C. Jones, F. Novarino, J. Spratt, C. T. Williams, and P. York (NHM) for their technical support, J. Corrie (Nottingham University) for helping us to set up the extraction apparatus. H. Taylor (NHM Photo Unit) is thanked for photographing T. involuta growing on U minerals. G. M. Gadd (Dundee University) and J. A. Elix (University of Canberra) are thanked for helpful advice regarding melanins. The present study was supported by a grant from the Natural History Museum to E.H.B. and O.W.P.