Colonization pattern in cryptoendolithic communities

Continental Antarctica ice-free areas are considered analogous environments of Mars, with liquid water largely absent, and hydrological cycle dominated by frozen ice and sublimated vapors. The main, and often the sole form of life in these cold deserts are cryptoendolithic microorganisms living inside exposed rocks, forming communities that inhabit rock airspaces which offer a protected microenvironment from the harsh external conditions. To further investigate the metabolic potential in these communities, we sequenced the metagenomes of 87 samples, recovering a total of 339 metagenome assembled genomes, which were annotated and used for construction of metabolic networks. Starting the construction of metabolic networks with a seed with 96 inorganic compounds, the reconstruction recovered a minimal community including six organisms (1 Chlorophyta, 1 Fungi, and 4 Bacteria’s), of which three (1 Chlorophyta and 2 Bacteria) are considered essential, with remaining being part of a pool of 27 alternative symbionts. This minimal community can produce 34 metabolites (plus five that can be reached by cooperation), including compounds that can be oxidized for energy. If these 39 metabolites obtained are added to the seed, the minimal community size jumps to 47 organisms, with 34 essential symbionts. This extended community can produce 960 metabolites (plus 210 reached by cooperation). This suggest that a microbial community can start the colonization of a substrate with no organic components, and after the primary stage of colonization by a small group of microorganisms, these create the conditions to the establishment of a community with a higher diversity and metabolic potential.

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