Abstract
Little is known about the viability of eukaryotic microorganisms preserved in icy regions. Here we report on the diversity of microbial eukaryotes in ice samples derived from four Pyrenean glaciers. The species composition of eukaryotic communities in these glaciers is unknown mostly because of the presence of a multi-year ice cap, and it is not clear whether they harbor the same populations. The recent deglaciation of these areas is allowing an easy access to glacial layers that correspond to the “Little Ice Age” although some isolated deposits are attributed to previous glacial cycles. In this study, we use molecular 18S rRNA-based approaches to characterize some of the microbial eukaryotic populations associated with Pyrenean glaciers. Firstly, we performed a chemical and microscopical characterization of ice samples. Secondly, molecular analyses revealed interesting protist genetic diversity in glaciers. In order to understand the microbial composition of the ice samples the eukaryotic communities resident in the glacial samples were examined by amplifying community DNA and constructing clone libraries with 18S rRNA primers. After removal of potential chimeric sequences and dereplication of identical sequences, phylogenetic analysis demonstrated that several different protists could be identified. Protist diversity was more phylum rich in Aneto and Monte Perdido glaciers. The dominant taxonomic groups across all samples (>1% of all sequences) were Viridiplantae and Rhizaria. Significant variations in relative abundances of protist phyla between higher and lower glaciers were observed. At the genus level, significant differences were also recorded for the dominant genera Chloromonas, Raphidonema, Heteromita, Koliella, and Bodomorpha. In addition, protist community structure showed significant differences between glaciers. The relative abundances of protist groups at different taxonomic levels correlated with the altitude and area of glaciers and with pH of ice, but little or no relationships to other chemical characteristics were found.
Highlights
Small eukaryotes are probably the most abundant eukaryotes on Earth
We report on the diversity of microbial eukaryotes in ice samples derived from four Pyrenean glaciers
Pigment and/or fatty acid analysis can provide some information on the structure and dynamics of the phototrophic and/or heterotrophic behavior of small eukaryotes, but the phylogenetic information supplied by these methods is limited (Lefranc et al, 2005)
Summary
Small eukaryotes are probably the most abundant eukaryotes on Earth. They have been found in all extreme environments (Caron et al, 1999), addressing a wide range of temperatures from tropical oceans (Li et al, 1994) to polar sea ice (Bachy et al, 2011). The discovery of cold-tolerant microorganisms in glaciated and permanently frozen environments has broadened the known range of environmental conditions which support microbial life These microorganisms that inhabit permanently cold ecosystems (representing one of the largest biosphere reserves on Earth) have been studied only for their ability to survive in such extreme conditions, recent studies have provided evidence that these habitats Several recent studies have analyzed the diversity of small eukaryotes, sampled in different cold ecosystems, by gene cloning and sequencing of rRNA genes and have shown high phylogenetic diversity (Lefranc et al, 2005). These studies identified a wide variety of lineages and retrieved sequences not clearly assigned to any known organisms. We report the diversity and distribution of microbial eukaryotes in four Pyrenean glaciers studied by 18S rRNA gene libraries and addresses some interesting questions: (i) what is the effect of altitude and glacier area on the composition of the microbial community? (ii) taking into account that ice melting is more dramatic in lower glaciers, which are the environmental differences associated to ice melting that affect microbial community? (iii) is it possible to discriminate between the effect on microbial community of area/altitude and the effect of chemical parameters? (iv) is it possible to find a microbial community or species to be used as an indicator of glacier retreat?
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