Antarctic cryptoendolithic bacterial lineages of pre-Cambrian origin as proxy for Mars colonization

Abstract

Cryptoendolithic communities are microbial ecosystems dwelling inside porous rocks. They are able to persist at the edge of the biological potential for life in the ice-free areas of continental Antarctica. These areas include the McMurdo Dry Valleys, often cited as a Terrestrial analog of the Martian environment. Despite their interest as a model for the early colonization by living organisms of terrestrial ecosystems and for adaptation to extreme conditions of stress, little is known about the evolution, diversity and genetic makeup of bacterial species that reside in these environments. We performed metagenomic sequencing of 18 communities from rocks collected in Antarctic desert areas over a distance of about 350 km. A total of 469 draft bacterial genome sequences were assembled, and clustered into 269 candidate species that lack a representative genome in public databases. The majority of these new species belong to monophyletic bacterial clades that diverged from related taxa in a range from 1.2 billion to 410 Ma, much earlier than the glaciation of Antarctica, and that are functionally distinct from known related taxa. The hypothesis that Antarctic cryptoendolithic bacterial lineages were generated by the selection of pre-existing cold-tolerant organisms whose origin dates back to the Tonian glaciations gives new insights for the possibility of life on Mars.

Stromatolites as Biosignatures of Atmospheric Oxygenation: Carbonate Biomineralization and UV-C Resilience in a Geitlerinema sp. - Dominated Culture

“…In the experimental set-up, the UV-C blocking microscope slide provides an abiotic type of shelter. In natural Early Earth and Mars analogs, porous rocks (Albanese et al, 2020), ice and dust (Rontó et al, 2003) might take a similar role. Geitlerinema filaments exclusively settled on the bottom side of the glass, as opposed to the positive control where mats formed on top of the slide (Figure 8B), closer to the PAR source.…”

Metabolomics of Dry Versus Reanimated Antarctic Lichen-Dominated Endolithic Communities

“…Endolithic communities are the main, if not the sole, life-forms representing the main standing biomass in the McMurdo Dry Valleys, occupying approximately 4% of sandstone boulders [ 12 ], up to 30% of granite boulders [ 13 ], and 100% of sandstone cliffs [ 1 ]. The most abundant and well characterized endolithic communities are those dominated by lichens [ 1 , 14 ] that are also a reservoir of endemic taxa [ 15 , 16 , 17 , 18 ]. These communities colonize porous rocks up to about 10 mm depth below the rock surface and microbial growth leads to differently colored bands, where each microbial component has different physiological adaptation and ecological abilities [ 1 ].…”

“…Only recently, Coleine et al [ 37 ] generated the first metagenomes from rocks collected in Continental Antarctica over a distance of about 350 km along an altitudinal transect from 834 up to 3100 m a.s.l. ; a total of 497 draft bacterial genomes were assembled and then clustered into 269 novel candidate species, functionally distinct from known related taxa species [ 17 ]. Friedmann and Ocampo-Friedmann [ 38 ] hypothesized that these microorganisms “hibernate” most of the time and activate the metabolism only when permissive climate conditions are reached in the summer season (e.g., when temperature rises, snow melts, and humidity increases), which anyway does not exceed 1000 h per year [ 39 ].…”