Dearing environment: yeast diversity in acidic aquatic systems

RUSSO GABRIEL; LIBKIND DIEGO; SAMPAIO JOSÉ P.; GADANHO MÁRIO; VAN BROOCK MARÍA R.

San Carlos de Bariloche

Simposio; International Biohydrometallurgy Symposium; 2009

Microbial biodiversity studies in extreme environments have increased in the last decades, including those focused on highly acidic habitats. However, very little is still known about yeasts inhabiting acidic aquatic environments. In this work we resume our investigations related to yeast diversity and ecology from highly acidic water bodies (pH<3) of natural (volcanic activity, Rio Agrio, Argentina) or anthropogenic origin (mining activity, Rio Tinto in Spain and São Domingos mine in Portugal). The extremely acidic waters of these aquatic systems were shown to harbor viable yeast cells in variable numbers (30-15,000 cells/L). In total, fifty yeasts species were identified of which eight were common to both type of acidic environments. Thirteen species showed interesting physiological properties (ability to survive in acidic waters of origin, growth in culture media formulated with such water, low optimum pH growth, high isolation frequency and high tolerance to heavy metals), and were proposed as autochthonous of acidic environments. Ten of them belonged to undescribed species, and hence are apparently specific to these extreme environments. Molecular phylogenetics showed that among these novel taxa, four Cryptococcus species able to thrive in extreme environmental conditions of low pH and high concentrations of heavy metals, constituted a separate phylogenetic clade/group which is here proposed as an ecoclade. Furthermore, another novel Cryptococcus species common to Argentinean and European acidic environments was found to possess an acidophilic behavior given its reduced ability to grow at pH higher than 3,5 and high resistance to most heavy metals tested. Thus, an interesting diversity of yeasts was revealed, including novel species which possess different levels of adaptation to the acidic environments. The bioprospection of these yeasts represents an important strategy to obtain agents for bioremediation processes and other fundamental and applied purposes.