Resistance of the Lichen Buellia frigidato Simulated Space Conditions during the Preflight Tests for BIOMEX—Viability Assay and Morphological Stability

摘要

Samples of the extremotolerant Antarctic endemite lichen Buellia frigida are currently exposed to low-Earth orbit–\udspace and simulated Mars conditions at the Biology and Mars Experiment (BIOMEX), which is part of the ESA\udmission EXPOSE-R2 on the International Space Station and was launched on 23 July 2014. In preparation for the\udmission, several preflight tests (Experimental and Scientific Verification Tests, EVT and SVT) assessed the sample\udpreparation and hardware integration procedures as well as the resistance of the candidate organism toward the\udabiotic stressors experienced under space and Mars conditions. Therefore, we quantified the post-exposure viability\udwith a live/dead staining technique utilizing FUN-1 and confocal laser scanning microscopy (CLSM). In addition,\udwe used scanning electron microscopy (SEM) to investigate putative patterns of morphological-anatomical damage\udthat lichens may suffer under the extreme exposure conditions. The present results demonstrate that Buellia frigida\udis capable of surviving the conditions tested in EVT and SVT. The mycobiont showed lower average impairment of\udits viability than the photobiont (viability rates of >83% and >69%, respectively), and the lichen thallus suffered no\udsignificant damage in terms of thalline integrity and symbiotic contact. These results will become essential to\udsubstantiate and validate the results prospectively obtained from the returning space mission. Moreover, they will\udhelp assess the limits and limitations of terrestrial organisms under space and Mars conditions as well as characterize\udthe adaptive traits that confer lichen extremotolerance.