Raman spectroscopic analysis of the calcium oxalate producing extremotolerant lichen Circinaria gyrosa

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.In the context of astrobiological exposure and simulation experiments in the BIOMEX project, the lichen Circinaria gyrosa was investigated by Raman microspectroscopy. Owing to the symbiotic nature of lichens and their remarkable extremotolerance, C. gyrosa represents a valid model organism in recent and current astrobiological research. Biogenic compounds of C. gyrosa were studied that may serve as biomarkers in Raman assisted remote sensing missions, e.g. ExoMars. The surface as well as different internal layers of C. gyrosa have been characterized and data on the detectability and distribution of β-carotene, chitin and calcium oxalate monohydrate (whewellite) are presented in this study. Raman microspectroscopy was applied on natural samples and thin sections. Although calcium oxalates can also be formed by rare geological processes it may serve as a suitable biomarker for astrobiological investigations. In the model organism C. gyrosa, it forms extracellular crystalline deposits embedded in the intra-medullary space and its function is assumed to balance water uptake and gas exchange during the rare, moist to wet environmental periods that are physiologically favourable. This is a factor that was repeatedly demonstrated to be essential for extremotolerant lichens and other organisms. Depending on the decomposition processes of whewellite under extraterrestrial environmental conditions, it may not only serve as a biomarker of recent life, but also of past and fossilized organisms.BMWi, 50WB1153, Analysen zur Stabilität und Degradation biogener Substanzen sowie zum Resistenzpotential der Fleche Buellia frigida unter simulierten Marsbedingungen und nach Exposition im LEO-Weltrau

Biosignature stability in space enables their use for life detection on Mars

Two rover missions to Mars aim to detect biomolecules as a sign of extinct or extant life with, among other instruments, Raman spectrometers. However, there are many unknowns about the stability of Raman-detectable biomolecules in the martian environment, clouding the interpretation of the results. To quantify Raman-detectable biomolecule stability, we exposed seven biomolecules for 469 days to a simulated martian environment outside the International Space Station. Ultraviolet radiation (UVR) strongly changed the Raman spectra signals, but only minor change was observed when samples were shielded from UVR. These findings provide support for Mars mission operations searching for biosignatures in the subsurface. This experiment demonstrates the detectability of biomolecules by Raman spectroscopy in Mars regolith analogs after space exposure and lays the groundwork for a consolidated space-proven database of spectroscopy biosignatures in targeted environments

Biosignature stability in space enables their use for life detection on Mars

Two rover missions to Mars aim to detect biomolecules as a sign of extinct or extant life with, among other instruments, Raman spectrometers. However, there are many unknowns about the stability of Raman-detectable biomolecules in the martian environment, clouding the interpretation of the results. To quantify Raman-detectable biomolecule stability, we exposed seven biomolecules for 469 days to a simulated martian environment outside the International Space Station. Ultraviolet radiation (UVR) strongly changed the Raman spectra signals, but only minor change was observed when samples were shielded from UVR. These findings provide support for Mars mission operations searching for biosignatures in the subsurface. This experiment demonstrates the detectability of biomolecules by Raman spectroscopy in Mars regolith analogs after space exposure and lays the groundwork for a consolidated space-proven database of spectroscopy biosignatures in targeted environments

Simulated Space Radiation: Impact of Four Different Types of High-Dose Ionizing Radiation on the Lichen Xanthoria elegans

This study addresses the viability of the lichen Xanthoria elegans after high-dose ionizing irradiation in the frame of the STARLIFE campaign. The first set of experiments was intended to resemble several types of galactic cosmic radiation (GCR) as present beyond the magnetic shield of Earth. In the second set of experiments, γ radiation up to 113 kGy was applied to test the limit of lichen resistance to ionizing radiation. Entire thalli of Xanthoria elegans were irradiated in the anhydrobiotic state. After STARLIFE 1, the metabolic activity of both symbionts was quantified by live/dead staining with confocal laser scanning microscopy. The photosynthetic activity was measured after the respective irradiation to assess the ability of the symbiotic green algae to restore photosynthesis after irradiation. The STARLIFE campaign complements the results of the LIFE experiments at the EXPOSE-E facility on the International Space Station by testing the model organism Xanthoria elegans on its resistance to hazardous radiation that might be accumulated during long-term space exposure. In addition, the photosynthetic activity of metabolically active lichen was investigated after X-ray irradiation up to 100 Gy (3.3 Gy/min). Since previous astrobiological experiments were mostly performed with anhydrobiotic lichen, these experiments will broaden our knowledge on the correlation of physiological state and astrobiological stressors

Desiccation and low temperature attenuate the effect of UVC254 nm in the photobiont of the astrobiologically relevant lichens Circinaria gyrosa and Buellia frigida

Several investigations on lichen photobionts (PBs) after exposure to simulated or real-space parameters consistently reported high viability and recovery of photosynthetic activity. These studies focused on PBs within lichen thalli, mostly exposed in a metabolically inactive state. In contrast, a recent study exposed isolated and metabolically active PBs to the non-terrestrial stressor UVC254 nm and found strong impairment of photosynthetic activity and photo-protective mechanisms (Meeßen et al. in 2014b). Under space and Mars conditions, UVC is accompanied by other stressors as extreme desiccation and low temperatures. The present study exposed the PBs of Buellia frigida and Circinaria gyrosa, to UVC in combination with desiccation and subzero temperatures to gain better insight into the combined stressors’ effect and the PBs’ inherent potential of resistance. These effects were examined by chlorophyll a fluorescence which is a good indicator of photosynthetic activity (Lüttge& Büdel in 2010) and widely used to test the viability of PBs after (simulated) space exposure. The present results reveal fast recovery of photosynthetic activity after desiccation and subzero temperatures. Moreover, they demonstrate that desiccation and cold confer an additional protective effect on the investigated PBs and attenuate the PBs’ reaction to another stressor – even if it is a non-terrestrial one such as UVC. Besides other protective mechanisms (anhydrobiosis, morphological–anatomical traits and secondary lichen compounds), these findings may help to explain the high resistance of lichens observed in astrobiological studies

The Effect of High-Dose Ionizing Radiation on the Astrobiological Model Lichen Circinaria gyrosa

The lichen Circinaria gyrosa is an astrobiological model defined by its high capacity of resistance to space conditions and to a simulated martian environment. Therefore, it became part of the currently operated BIOMEX experiment on board the International Space Station and the recent STARLIFE campaign to study the effects of four types of space-relevant ionizing radiation. The samples were irradiated with helium and iron ions at doses up to 2 kGy, with X-rays at doses up to 5 kGy and with γ rays at doses from 6 to 113 kGy. Results on C. gyrosa's resistance to simulated space ionizing radiation and its post-irradiation viability were obtained by (i) chlorophyll a fluorescence of photosystem II (PSII), (ii) epifluorescence microscopy, (iii) confocal laser scanning microscopy (CLSM), and (iv) field emission scanning electron microscopy (FESEM). Results of photosynthetic activity and epifluorescence show no significant changes up to a dose of 1 kGy (helium ions), 2 kGy (iron ions), 5 kGy (X-rays)—the maximum doses applied for those radiation qualities—as well as a dose of 6 kGy of γ irradiation, which was the lowest dose applied for this low linear energy transfer (LET) radiation. Significant damage in a dose-related manner was observed only at much higher doses of γ irradiation (up to 113 kGy). These data corroborate the findings of the parallel STARLIFE studies on the effects of ionizing radiation on the lichen Circinaria gyrosa, its isolated photobiont, and the lichen Xanthoria elegans

UV-C tolerance of symbiotic Trebouxia sp. in the space-tested lichen species Rhizocarpon geographicum and Circinaria gyrosa: role of the hydration state and cortex/screening substances

Many experiments were carried out in order to evaluate the survival capacity of extremotolerant lichens when facing harsh conditions, including those of outer space or of simulated Martian environment. For further progress, a deeper study on the physiological mechanisms is needed that confer the unexpected levels of resistance detected on these symbiotic organisms. In this work, the response of the lichenized green algae Trebouxia sp. (a predominant lichen photobiont) to increasing doses of UV-C radiation is studied. UV-C (one of the most lethal factors to be found in space together with vacuum and cosmic-ionizing radiation with high atomic number and energy (HZE) particles) has been applied in the present experiments up to a maximum dose analogue to 67 days in Low Earth Orbit (LEO). For that purpose we selected two extremotolerant and space-tested lichen species in which Trebouxia sp. is the photosynthetic partner: the crustose lichen Rhizocarpon geographicum and the fruticose lichen Circinaria gyrosa. In order to evaluate the effect of the physiological state of the lichen thallus (active when wet and dormant when dry) and of protective structures (cortex and photoprotective pigments) on the resistance of the photobiont to UV-C, four different experimental conditions were tested: (1) dry intact samples, (2) wet intact samples, (3) dry samples without cortex/acetone-rinsed and (4) wet samples without cortex/acetone-rinsed. After irradiation and a 72 hours period of recovery, the influence of UV-C on the two lichen’s photobiont under each experimental approach was assessed by two complimentary methods: (1) By determining the photosystem II (PSII) activity in three successive 24 hours intervals (Mini-PAMfluorometer) to investigate the overall state of the photosynthetic process and the resilience of Trebouxia sp. (2) By performing high performance liquid chromatography (HPLC)-quantification of four essential photosynthetic pigments (chlorophyll a, chlorophyll b, β-carotene and lutein) of one sample of each species and dose. Results indicate that the physiological state of the thallus is the most important factor impairing the tolerance of Trebouxia sp. to UV-C radiation in both lichen species. Desiccated thalli were demonstrated to be more resistant to UV-C. No clear influence of UV-C radiation on the carotenoid content was detected. Comparing the respective doses applied, the individuals of R. geographicum are more sensitive than C. gyrosa