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Identifier 000418830
Title Βιοενεργητική μελέτη της ακραιοφιλικής συμπεριφοράς του χλωροφύκους Trebouxia crenulata στα πλαίσια συμβίωσής του με μεθυλοβακτήριο
Alternative Title Bioenergetic study of the extremophilic behavior of the green alga Trebouxia crenulata in symbiosis with a methylobacterium
Author Τύμπα Λύδα-Ελένη Λ.
Thesis advisor Κοτζαμπάσης, Κυριάκος
Thesis advisor Πυρίντζος, Στέργιος
Φλεμετάκης, Εμμανούηλ
Abstract This work focuses on the extremophilic behavior of the unicellular green alga Trebouxia crenulata, which is the photobiont of Ramalina capitata lichen species. The algal strain that was isolated from the lichen thallus, showed an unexpected mutualistic interaction with a potentially photosynthetic bacterial strain, as derived from the spectral characterization of its pigments. The populations of the two interacting microorganisms coexisted and although each population outnumbered the other under different circumstances, both of them remained viable and robust. A rise in the bacterial population was able to accelerate the otherwise low growth rate of the algae. In order to elucidate whether the observed interaction affects the extremotolerance of the algae in a positive or negative fashion, we comparatively investigated the response of this mutualistic scheme to extreme salinity, low temperature and dessication, in contrast to the response of each partner separately. Interestingly, the mutualistic scheme exhibited remarkable tolerance to salinity up to 50‰, since, after 66 hours of incubation in the respective medium, the photosynthetic apparatus of the algae remained completely functional, while the bacteria showed normal growth on petri dishes. Extreme low temperature (-196 oC/ 77K) and dessication had the same effect on both microorganisms, indicating compatibility in their extremotolerance ranges. The bacterial strain belongs to the genus Methylobacterium, according to its 16S rRNA sequenced region, while its species specific rpoΒ region sequence shows 94% similarity with the respective region of Methylobacterium populi. This particular species has been described to promote plant growth through producing IAA and detoxifying its environment. In the repetition of the above abiotic stress experiments on axenic cultures of T. crenulata (after successfully isolating the strain), the algae failed to cope with the extreme conditions adequately to the mutualistic scheme. As is evident from the overall results, the studied bacterial-algal interaction has a positive impact on the extremotolerance of T. crenulata. Moreover, the mutualistic scheme as well as the axenic algal culture failed to produce hydrogen (H2) in anaerobic conditions. This is in accordance with previous results from our lab, which indicate that lichen species of the genus Ramalina tested for hydrogen production, were the only ones that failed to exhibit considerable amounts of hydrogen. In order to propose a specific mechanism of the above mutualism, in addition to elucidating the possibility of the two microorganisms coexisting in lichen microecosystems, thorough molecular and biochemical analysis is to be performed.
Language Greek
Subject Extremotolerance
Ακραιοφιλία
Issue date 2018-11-23
Collection   School/Department--School of Sciences and Engineering--Department of Biology--Post-graduate theses
  Type of Work--Post-graduate theses
Permanent Link https://elocus.lib.uoc.gr//dlib/d/f/7/metadata-dlib-1540193791-777003-15135.tkl Bookmark and Share
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