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de Vera, J. P.; Ott, S.; de la Torre, R.; Sancho, L. G.; Horneck, G.; Rettberg, P.; Ascaso, C.; de los Ríos, A.; Wierzchos, J.; Cockell, C.; Olsson, K.; Frías, J. M. and Demets, R.
(2009).
DOI: https://doi.org/10.1007/s11084-009-9164-7
Abstract
In the context of Lithopanspermia investigations have been performed to investigate the ability of different organisms to resist scenarios of the natural interplanetary transfer of life from a donor planet (host planet) to an acceptor planet. Whereas the main focus of previous studies was on the resistance of bacteria and their colony forming capacity after space exposure, only a few experiments on eukaryotic microorganisms and especially on symbiotic organization forms such as lichens, have been performed in space (de la Torre et. al. 2007, Sancho et al. 2007). These experiments have concentrated on photosynthesis analysis as a first step to understand the maintenance of physiologic activity of eukaryotic organisms after exposure to space conditions. As a next step, physiologic activity, reproduction capacity and “healthy” cell structures as essential parts of vitality check were analyzed after the last ESA experiment on BIOPAN-6 on Foton M3. Besides the examination of photosynthetic activity determination by use of chlorophyll a-fluorescence, CLSM analysis by the use of LIVE/DEAD staining dyes and culture experiments for verification of germination and growth capacity of both of the lichen symbionts (alga and fungi), were performed. In this case, new results are now clearly emphasizing quantitatively the high survival capacity and maintenance of germination and growth capacity of both of the investigated symbionts which form the epilithic lichen species of Rhizocarpon geographicum and Xanthoria elegans, although they were exposed to harsh space conditions with an exposure time of 10 days. About 80% to 90% of ascospores of both of the analyzed lichens were able to germinate and to grow into well-developed mycelia. In detail: results of germination and growth capacity analysis of ascospores of the lichen X. elegans have shown no damage on growth behavior, if compared to the control analysis, differing only in the starting point of germination, which is about 1 to 2 days earlier than under control conditions (1 to 2 days after sporulation instead of 2 to 4 days). Results of analysis on ascospores of R. geographicum indicate an important role of desiccation for successful germination. Without the vacuum treatment in space, the control samples were not able to germinate. This implicates the necessity of very dry conditions for the break down of ascosporic cell walls to foster the ability of germination, what can be expected also in natural habitats (high mountain regions). Analyses on the growth multiplication factor of photobiont cells (alga) are indicating a higher degree of space influence on X. elegans. Photobiont cells of R. geographicum maintained their doubling rate of about 12 days compared to control conditions, whereas the doubling rate of photobiont cells of X. elegans was seriously affected after space exposure, showing a severe retardation (control conditions: doubling rate (dr)=7 days, after space exposure: dr=12 days).
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