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Identifier 000403419
Title Μελέτη της ακραιόφιλης συμπεριφοράς του λειχήνα Pleurosticta acetabulum με αστροβιολογικές εφαρμογές
Alternative Title Study of extremophilic behaviour of lichen Pleurosticta acetabulum with astrobiologial application
Author Παρασύρη, Αθηνά Κ.
Thesis advisor Κοτζαμπάσης, Κυριάκος
Reviewer Πυρίντσος, Στέργιος
Βόντας, Ιωάννης
Abstract The purpose of this work is to demonstrate the resistance of lichen under prolonged drought stress, extremely low temperature (-196oC) and oxygen depleted conditions, using a series of biochemical and physicochemical analyses and physiological/ functional approaches. The lichen Pleurosticta acetabulum is revived after exposure to a long period of drought. In fact, the transition to the dry state, not only did not stress the lichen, but also contributed to its structural and functional maintenance, when incubated at -196oC. Fluorescence induction measurements (JIP test) and HPLC analyses of ergosterol levels confirmed the maintenance of both symbionts. On the contrary, the incubation of metabolically active lichen at extremely low temperature stressed the photobiont Trebouxia, without leading to collapse and the mycobiont partner remained intact. The isolated green algae, Trebouxia, in a non-symbiotic state, was not stressed at all when exposed at drought stress and the extremely low temperature of -196oC, proving the fact that the isolated algae is as resistant as the whole lichen thalli at extreme conditions. The above results confirm that the resistance of the lichen is not directly an effect of the symbiosis between the photobiont and the mycobiont, in contrast to the hitherto predominant acceptance, but they are two equal resistant organisms. The incubation of the lichen in absolute dry conditions and extremely low temperature was followed by incubation in oxygen depleted conditions. In this state, the lichen remained functional and its metabolism, and especially its photosynthetic activity, was reorganized, leading to the production of high amount of molecular hydrogen (H2) through the dark fermentation pathway, which combines the lipid biosynthesis pathway with the electron transport chain of photosynthesis. Neither the drought nor the extremely low temperature affected the ability of lichen to produce high amounts of hydrogen in oxygen depleted conditions, which can be used as fuel to meet energy demands and has high efficiency. The thorough analysis of differentiation in the level of fats and their fatty acids composition, as well as the level of sugar in all treatments contributed to the understanding of the extremophilic behavior of lichen. The unprecedented resistance and functional plasticity of this organism in three extreme conditions that simulate space conditions, makes it the ideal organism for space missions and astrobiological/astrobiotechnological applications. Based on the results of this study, the theory of panspermia can be further analyzed and lichens are suggested as the organisms that could both accompany a space mission by providing energy at zero cost and also be used in a Reverse Assisted Panspermia, carrying life in other star systems.
Language Greek
Subject Astrobiology
Hydrogen production
Παραγωγή υδρογόνου
Issue date 2016-11-18
Collection   School/Department--School of Sciences and Engineering--Department of Biology--Post-graduate theses
  Type of Work--Post-graduate theses
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