242 Geobiology & Geomicrobiology (Posters)

Wednesday, 12 October 2011
9:00 AM - 6:00 PM
Hall C

MN OXIDE BIOMINERALIZATION BY FUNGI IN SOUTHERN APPALACHIAN CAVES

Paper number: 242-3
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

Caves in the southern Appalachians commonly have thin manganese (Mn) oxide coatings on their walls, on pebbles and cobbles in streams and pools, and on flowstone associated with springs and seeps. These mineral coatings are frequently associated with bacterial communities, suggesting that microbial activity plays a role in the precipitation of Mn oxides (through the oxidation of Mn(II) compounds). Until now, the contribution of fungi to this Mn biomineralization process in caves has been largely overlooked. In our studies of several caves in southern Appalachians, we cultured several species of Mn-oxidizing Ascomycete fungi . The cave systems include Rye Cove - Cox Ridge Cave and Daniel Boone Caverns in southwest Virginia and Carter Salt Peter Cave in east Tennessee, all located in the Ordovician Knox Dolomite unit. Sample locations were selected by the presence of a black or brownish black coating or biofilm coating the cave walls and floors, or growing on exogenous materials left in the cave by human and animal visitors (tape, socks, feces), and Mn oxidation was confirmed in the field using the leucoberbelin blue (LBB) assay, a colorless chemical compound that turns bright blue in the presence of Mn(III) or Mn(IV) compounds.

Cultured fungal samples were analyzed by light microscopy as well as scanning and transmission electron microscopy. TEM imaging and EDS analysis has revealed that in several samples, Mn oxidation only occurs within the fungal hyphae cells, particularly along hyphae where new hyphal branches are forming. In other samples it appears to be forming crumped sheets surrounding the exterior of the hyphae. In one sample, fruiting bodies appear to be oxidizing in addition to the hyphae. Mn oxides in fungal spores have not been observed at this time in any samples.

Mn oxides produced by fungal cultures are poorly crystalline and appear amorphous to laboratory-based X-ray sources. Interestingly, tentative crystallographic identifications by single crystal micro-X-ray diffraction indicate that buserite (a layered Mn oxide) is the dominant mineral present in a sample isolated from a biofilm in a stream in Carter Salt Peter Cave.