Yeast diversity in the hyper-acidic aquatic systems of the Iberian Pyrite Belt

LIBKIND FRATI, D; GADANHO, M; SAMPAIO, JP

Caviahue, Nqn

Workshop; Interdisciplinary Workshop in Geogenically Acidic Water Systems: Volcanic Waters, Mining Lakes and Rivers; 2004

Yeasts are unicellular fungi well adapted to grow in water-rich habitats and little is known about their biodiversity and ecology in aquatic environments, even less in extreme acidic systems. Yeast isolates from these extreme environments might have interesting properties for bioremediation and since yeasts are considered eukaryotic models they may be a suitable subject for studying mechanisms of heavy metal tolerance under acidic conditions. Examples of acidic environments as result of anthropogenic activity are located in the vast mining area in the South of Portugal and Spain, where one of the most important pyrite regions in the world is located, the Iberian Pyrite Belt (IPB) . Here, acid rock drainage contaminates soils and groundwater resulting in acidic (pH 1.5-2.5) reddish-brown waters with high concentrations of metals (Fe, Mg, Pb, Cu, Zn). We studied 3 ponds formed by flooding of abandoned mines at San Domingos (Portugal) and several sites at the Rio Tinto (Spain) for yeast occurrence. The classical filtration-culturing method was employed and simultaneously an unculturing-dependent method was preliminary tested. This latter technique was based on the direct extraction of DNA from environmental enriched samples, PCR amplification of a 26S rDNA partial sequence with fungi specific primers, Temperature Gradient Gel Electrophoresis (TGGE) for band separation and sequencing of the bands. The isolates obtained using the classical methods were grouped by PCR fingerprinting (MSP-PCR) and representatives of each group were then sequenced on their D1/D2 26S rDNA region. Yeast cell counts were variable for both the San Domingos mines and the Rio Tinto, values ranged 0 - 3500 cells/ L or 17- 827 cells/L, respectively. We found that acidic aquatic environments of the IPB support a considerable yeast diversity dominated by basidiomycetous species including many undescribed species. Both methods employed rendered similar results. The yeast communities at San Domingos mines and Tinto river were similar. This suggests that the yeast species found are particularly adapted to these extreme environments. Then comparisons with natural acidic environments such as the Agrio - Caviahue system are desirable.