International Journal of Astrobiology 14 (3): 411–425 (2015) doi:10.1017/S1473550414000214 © Cambridge University Press 2014 Viability of the lichen Xanthoria elegans and its symbionts after 18 months of space exposure and simulated Mars conditions on the ISS Annette Brandt1, Jean-Pierre de Vera2, Silvano Onofri3 and Sieglinde Ott1 1Institute of Botany, Heinrich-Heine-University, Universitätsstr. 1, 40225 Düsseldorf, Germany 2Institute of Planetary Research, German Aerospace Center (DLR), Rutherfordstr. 2, 12489 Berlin, Germany 3Department of Ecological and Biological Sciences (DEB), Tuscia University, Largo dell’Università, 01100 Viterbo, Italy e-mail:
[email protected] Abstract: The lichen Xanthoria elegans has been exposed to space conditions and simulated Mars-analogue conditions in the lichen and fungi experiment (LIFE) on the International Space Station (ISS). After several simulations and short space exposure experiments such as BIOPAN, this was the first long-term exposure of eukaryotic organisms to the hostile space conditions of the low Earth orbit (LEO). The biological samples were integrated in the EXPOSE-E facility and exposed for 1.5 years outside the ISS to the combined impact of insolation, ultraviolet (UV)-irradiation, cosmic radiation, temperatures and vacuum conditions of LEO space. Additionally, a subset of X. elegans samples was exposed to simulated Martian environmental conditions by applying Mars-analogue atmosphere and suitable solar radiation filters. After their return to Earth the viability of the lichen samples was ascertained by viability analysis of LIVE/DEAD staining and confocal laser-scanning microscopy, but also by analyses of chlorophyll a fluorescence. According to the LIVE/DEAD staining results, the lichen photobiont showed an average viability rate of 71%, whereas the even more resistant lichen mycobiont showed a rate of 84%.