Metabolic responses in opposite sun-exposed Antarctic cryptoendolithic communities.

Antarctic cryptoendolithic communities are self-supporting borderline ecosystems spreading across the extreme conditions of the Antarctic desert and represent the most predominant life-form in the ice-free desert of McMurdo Dry Valleys, accounted as the closest terrestrial Martian analogue. Components of these communities are very adapted extremophiles and extreme-tolerant microorganisms, among the most resistant known to date. Recent advances started to investigate the biodiversity and community composition in these microbial ecosystems but the metabolic activity of the metacommunity has never been investigated to date. In this study, we explored the stress-response, spreading in two different sites of the same location, subjected to increasing environmental pressure due to opposite sun exposure, to verify the effect of sunlight on settlement and adaptation strategies. Results indicated that the metabolic responses are shaped according to external conditions; in the overall 252 altered metabolites (56 and 196 unique for north and south, respectively), distinguished the two differently exposed communities. We also selected 10 metabolites and performed two-stage Receiver Operating Characteristic (ROC) analysis to test them as potential biomarkers. We focused further on melanin and allantoin as protective substances; their concentration was highly different in the community in the shadow or in the sun.