Abstract EANA2025-135

The ice-free areas of continental Antarctica represent analogous environments of Mars, with a hydrological cycle dominated by frozen ice and sublimated vapors, and liquid water largely absent. The main, and often the sole form of life in these cold deserts is represented by microorganisms living inside exposed rocks forming endolithic communities, which inhabit rock airspaces that offer a protected microenvironment from the extremely harsh external conditions. Previous studies suggest that these organisms includes metabolic versatile aerobes that use hydrogen for respiration and carbon fixation, with similar core primary carbon metabolism patterns in soil and endolithic communities, with the last seemingly supported by trace gas oxidation and atmospheric chemosynthesis. To further investigate the energy production in communities in colonized pore spaces in sandstones (cryptoendolithic) in dry areas along an altitudinal gradient from 900-3,000 m asl, we assembled WGS metagenomes from 36 samples, predicted and annotated prokaryotic and eukaryotic genes, and analyzed the occurrence of genes related to different KEGG energy production pathways. The most completely represented metabolic pathways were oxidative phosphorylation, followed by methane metabolism, other forms of carbon metabolism, photosynthesis, sulfur metabolism, and nitrogen metabolism. Preliminary metagenome read classification by genera using Kraken 2 Archaea, Bacteria, and Fungi databases plus the reference genomes of Chlorophyta were further explored using a database about energy metabolism in different microorganism genera compiled from Bacdive and a number of other references. The results indicate that aerobic bacteria represent between 37-68% classified reads and anaerobics 7.8-23.5%, with autotrophic organisms representing 26-61% of the total. On average, the predominant autotrophic form of energy production is aerobic photosynthesis (16-58% of the reads, mainly Chlorophyta, with predominance of the genera Trebouxia), followed by anaerobic photosynthesis (1-5.7%), sulfur oxidation (0.6-3.4%), denitryfication (0.6-3.1%), sulfur reduction (0.4-2.5%), nitrogen fixation (0.4-2.2%), methanotrophism (0.05-0.37%), nitrification (0.02-0.12%), and methanogenesis (0.003-0.024%). The ratio between aerobic photosynthesis and other autotrophic forms ranged from 1.5-56.3x (mean 18.8x), with a strong negative Spearman correlation (rho = -0.99, p < 0.01) between the quantification of organisms that perform aerobic photosynthesis in relation to the combined of the other autotrophic energy forms. The quantities of anaerobic bacteria also showed a strong negative Spearman correlation (rho = -0.99, p < 0.01) in relation to the quantities of organisms that perform aerobic photosynthesis. These results indicate a pronounced influence of the presence of organism that perform aerobic photosynthesis in the studied cryptoendolithic communities, with the decrease in the abundance of these being correlated with increases in the abundance of organisms that utilize other forms of autotrophic energy production and anaerobic bacteria. This turnover between forms of energy production related to the prevalence of aerobic photosynthesis shows the remarkable adaptation capacity found in these self-sustaining communities, suggesting that these microorganism assemblages could also be structured around other primary producers, as those that perform anoxygenic photosynthesis or chemosynthesis.