Resistenza agli stress e sopravvivenza in ambiente spaziale di funghi criptoendolitici antartici
Author(s)
Barreca, Donatella
Date Issued
October 24, 2008
Type
Doctoral Thesis
Abstract
In the McMurdo Dry Valleys, ice-free desert of continental Antarctica, stressful environmental conditions coexist, often compared to those found on early Mars. In such conditions, lichenized fungi and algae, black meristematic fungi, bacteria, cyanobacteria and non lichenized algae are able to survive in the airspaces of porous rocks, forming the “lichen-dominated cryptoendolithic community”. Three strains of black meristematic fungi of the genus Cryomyces, two of C. antarcticus and one of C. minteri, that colonize such communities, were subjected to specific tests. They demonstrated an elevated resistance to several stress factors, such as ultraviolet radiation, high salt concentration and
desiccation, growing significantly when exposed to 10h of UV-B irradiation (108 kJm-2),
concentrations of 3.5 to 24% of NaCl, as well as 7 repeated cycles of freezing and thawing
at 5 different temperatures (from 0 to -25°C). Such resistance is due, among other things, to
the thick melanized walls of their isodiametric cells and to the presence of extra-cellular
polymeric substances surrounding the hyphae. For this reason black meristematic fungi
found in Antarctica constitute a unique model for testing the limits to which life on Earth
can still be possible, thus suggesting their use, along with lichen-dominated cryptoendolithic communities, as a study model in exobiology. The Experiment Verification Tests (EVTs) carried out at the German Aerospace Center (DLR) of Cologne
(DE), regarding the application of space and simulated Mars conditions on the three fungal strains and colonized Antarctic rock fragments, have demonstrated a formidable resistance after desiccation of these experimental models to space vacuum, radiations, and simulated Mars atmosphere; they, in fact, have shown to survive either to space simulation tests like vacuum (10-5 Pa for 1h and 1 week), repeated freezing and thawing cycles (from -20 °C to +20 °C for two weeks), UV-C (254 nm to 10 Jm-2, 100 Jm-2 and 1000
Jm-2) and total UV (200-400 nm, at 1,5, 1,5×103 and 1,5×105 kJm-2), to Martian environmental conditions (600 Pa CO2), and also to a combination of these. The tests carried out have allowed to identify the more suitable samples to be used in the LIFE experiment (LIchens and Fungi Experiment) in space, and to formulate the first
hypotheses on their ability to resist to extraterrestrial conditions. The LIFE program, born from a collaboration between Italy, Germany, and Spain (within Expose-EuTEF of the ESA) proposes to assess the long term resistance of Antarctic cryptoendolithic organisms and epilithic lichens, by exposing them for a period of approximately 1.5 years on the International Space Station (ISS) to Martian external space and environmental conditions.
Additional information
Dottorato di ricerca in Evoluzione biologica e biochimica
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