Sequences of psychrophilic fungi amplified from glacier-preserved ascolichens

Abstract

Ribosomal DNA sequences were amplified from subfossils of the ascolichen Umbilicaria cylindrica (L.) Delise ex Duby collected at the ablating edges of Greenland glaciers. Surprisingly, phylogenetic analysis indicated that the amplified rDNA sequences were not closely related to those of the lichen-forming fungus but rather represented two groups of psychrophilic basidiomycetes (orders Cystofilobasidiales and Sporidiales) and one group of ascomycetes (order Leotiales). Two of these groups, the Sporidiales and the Leotiales, include other fungi previously detected in DNA extracted from the grass clothing of the Tyrolean Iceman desiccated and frozen for over 3000 years and also in 2000- and 4000-year-old ice core samples from northern Greenland. Large subunit ribosomal DNA sequences representing the group Cystofilobasidiales were nearly identical to those of the basidioyeast saprobe Mrakia frigida. The adjacent internal transcribed spacer sequence was more than 98% similar to those from three samples of U. cylindrica from different sites that had been subjected to ice burial for various lengths of time, suggesting they also were Mrakia sequences. Although ancient contamination of multiple U. cylindrica specimens with fungi such as Mrakia cannot be ruled out, it is more probable that saprobic colonization of the subfossil tissues by psychrophilic fungi proceeded during recent ice melt.Key words: ancient DNA, small subunit ribosomal DNA, 18S ribosomal DNA, phylogenetic analysis, psychrophilic fungi, lichen-forming fungi.