Life on top: cryptoendolithic ascomycetes and microalgae isolated from over 6000 m altitude

Rocks are among the oldest terrestrial niches hosting a multiplicity of life forms, of which diversity has been only partially uncovered. Endolithic metacommunities comprise all major groups of microorganisms, such as chemo-organotrophic, chemo-lithotrophic and phototrophic, represented by bacteria, microalgae and microfungi. Their diversity is often difficult to describe and may remain underestimated. Furthermore, knowledge about the diversity of microorganisms colonizing rocks in peculiar niches is even poorer due to the difficulty to retrieve environmental specimens. Here, we report the phylogenetic and phenotypic characterization of a few endolithic fungi and algae isolated from rock fragments collected at high elevation, i.e., on the top of two mountains over 6000 m altitude, Muztagh Ata (China) and Cerro Mercendario (Argentina). The identity of the strains was confirmed by sequencing the nuclear ITS and LSU, the plastidial rbcL loci and by morphological analysis. Three fungal strains belonging to the class Dothideomycetes and one algal strain belonging to the genus Trebouxia were isolated from Muztagh Ata, while six fungal strains belonging to the order Chaetothyriales and four algal strains belonging to the genus Myrmecia were isolated from Cerro Mercedario. The detected species diversity is discussed in an evolutionary and ecological context.