Lichens are an association of a photoautotrophic alga/cyanobacteria (photobiont) and a heterotrophic fungus (mycobiont) constituting the lichen thallus as a complex phenotype. Many mycobionts ...reproduce sexually and the ascospores are dispersed without the photobiont. For successful re-lichenization the specific photobiont must be recognized, contacted, and incorporated by the mycobiont. A so-called pre-contact stage has been postulated as the initial step of a gradual recognition process. In the present study, the effect of the specific Trebouxia photobiont, an unspecific Asterochloris photobiont and the non-lichenizing green alga Myrmecia bisecta on the development of the mycobiont Fulgensia bracteata was assessed by pre-contact assays. Three hypotheses were confirmed: (i) the pre-contact stage exists, (ii) it is characterized by morphological reactions in the development of the mycobiont, and (iii) the reactions depend on the interacting alga. Control conditions revealed a mycelial growth arrest but this effect was not observed in the presence of any of the three algae. Different algae induce distinct growth patterns with respect to hyphal length, morphological characteristics, and formation of mucilage. The specific Trebouxia photobiont had a positive impact on hyphal growth, branching frequency, and mucilage formation. These effects were less explicit with the non-specific Asterochloris photobiont. Myrmecia bisecta induced uncharacteristic growth patterns with pronounced hyphal growth and high numbers of aerial hyphae but less formation of mucilage. These results indicate that symbiont recognition mechanisms are established before physical contact. Pre-contact reactions may be an evolutionary advantage that supports the persistence of the mycobiont on newly colonized sites and improves the probability of re-lichenization.
The lichen Buellia frigida was exposed to space and simulated Mars analog conditions in the Biology and Mars Experiment (BIOMEX) project operated outside the International Space Station (ISS) for 1.5 ...years. To determine the effects of the Low Earth Orbit (LEO) conditions on the lichen symbionts, a LIVE/DEAD staining analysis test was performed. After return from the ISS, the lichen symbionts demonstrated mortality rates of up to 100% for the algal symbiont and up to 97.8% for the fungal symbiont. In contrast, the lichen symbiont controls exhibited mortality rates of 10.3% up to 31.9% for the algal symbiont and 14.5% for the fungal symbiont. The results performed in the BIOMEX Mars simulation experiment on the ISS indicate that the potential for survival and the resistance of the lichen B. frigida to LEO conditions are very low. It is unlikely that Mars could be inhabited by this lichen, even for a limited amount of time, or even not habitable planet for the tested lichen symbionts.
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. Key Words: Astrobiology-Extremotolerance-Gamma rays-Ionizing radiation-Lichens-Viability. Astrobiology 17, 136-144.
As part of the ESA space experiment BIOMEX (Biology and Mars Experiment) the lichen Buellia frigida has been exposed to space and simulated Mars analogue conditions on the expose facility EXPOSE-R2 ...placed outside the Russian Zvezda module on the International Space Station (ISS) for 1.5 years. Randomly Amplified Polymorphic DNA (RAPD) technique has been carried out to study the effect of space conditions on the DNA integrity as well as to assess DNA damage. The RAPD profiles of the space exposed lichen samples demonstrate conspicuous changes compared to the control profiles. For the survival of cells and entire organisms the DNA integrity is an essential prerequisite. The results of the study presented indicate a minor resistance potential of the lichen Buellia frigida towards Low Earth Orbit and Mars analogue conditions effecting the survival potential and the resistance of the symbiotic organism.
•Innovative knowledge on the DNA integrity of Buellia frigida after exposition to space conditions.•Space and Mars-like conditions clearly cause damages on the DNA level in the Antarctic lichen.•There is an obvious minor resistance potential of Buellia frigida to LEO space conditions.
Successful re-lichenization between the two bionts of the lichen symbiosis, the fungal mycobiont and its specific photobiont, is a process that is not well understood yet. To assess potential ...signalling between the two bionts during initial pre-contact, exudates of the
Trebouxia
photobionts of
Fulgensia bracteata
,
Fulgensia fulgens
, and
Xanthoria elegans
, of the
Asterochloris
photobiont of
Lecidea lurida
, and of the non-lichenizing green alga
Myrmecia bisecta
were investigated. The compounds identified in these exudates were tested with respect to their influence on germination and early development of the
Fulgensia bracteata
mycobiont. Additionally, carbohydrates (glucose, sucrose, ribitol) were tested to appraise their effect on the mycobiont growth patterns. Three hypotheses were confirmed: (i) photobionts exude various substances, (ii) the photobiont exudation pattern varies with the identity of the photobiont, and (iii) a pre-contact influence induces changes in the early development of the mycobiont of
F. bracteata
. This study gives comparative insight to exudates of lichen photobionts. In vitro photobionts differentially release compounds belonging to several substance classes which include indole-3-carbaldehyde, two cyclic dipeptides, and rhamnose. Two compounds had inhibitory effects on germination and germ-tube growth of the mycobiont and one other enhanced spore germination. Additionally, ribitol was found to elicit a strong effect on the mycobiont’s growth. In general, photobiont-exudation, its effect on the mycobiont, and the response to ribitol suggest that complex pre-contact signalling has a crucial role in lichen biont recognition.
Lichen symbioses between fungi and algae represent successful life strategies to colonize the most extreme terrestrial habitats. Consequently, space exposure and simulation experiments have ...demonstrated lichens' high capacity for survival, and thus, they have become models in astrobiological research with which to discern the limits and limitations of terrestrial life. In a series of ground-based irradiation experiments, the STARLIFE campaign investigated the resistance of astrobiological model organisms to galactic cosmic radiation, which is one of the lethal stressors of extraterrestrial environments. Since previous studies have identified that the alga is the more sensitive lichen symbiont, we chose the isolated photobiont Trebouxia sp. of the astrobiological model Circinaria gyrosa as a subject in the campaign. Therein, γ radiation was used to exemplify the deleterious effects of low linear energy transfer (LET) ionizing radiation at extremely high doses up to 113 kGy in the context of astrobiology. The effects were analyzed by chlorophyll a fluorescence of photosystem II (PSII), cultivation assays, live/dead staining and confocal laser scanning microscopy (CLSM), and Raman laser spectroscopy (RLS). The results demonstrate dose-dependent impairment of photosynthesis, the cessation of cell proliferation, cellular damage, a decrease in metabolic activity, and degradation of photosynthetic pigments. While previous investigations on other extraterrestrial stressors have demonstrated a high potential of resistance, results of this study reveal the limits of photobiont resistance to ionizing radiation and characterize γ radiation-induced damages. This study also supports parallel STARLIFE studies on the lichens Circinaria gyrosa and Xanthoria elegans, both of which harbor a Trebouxia sp. photobiont. Key Words: Astrobiology-Gamma rays-Extremotolerance-Ionizing radiation-Lichens-Photobiont. Astrobiology 17, 154-162.
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. Key Words: Simulated space ionizing radiation-Gamma rays-Extremotolerance-Lichens-Circinaria gyrosa-Photosynthetic activity. Astrobiology 17, 145-153.
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.
Biomolecules were preserved under martian conditions simulated on the ISS and their analysis supports the search for life on Mars.
The Low Earth Orbit (LEO) experiment Biology and Mars Experiment (BIOMEX) is an interdisciplinary and international space research project selected by ESA. The experiment will be accommodated on the ...space exposure facility EXPOSE-R2 on the International Space Station (ISS) and is foreseen to be launched in 2013. The prime objective of BIOMEX is to measure to what extent biomolecules, such as pigments and cellular components, are resistant to and able to maintain their stability under space and Mars-like conditions. The results of BIOMEX will be relevant for space proven biosignature definition and for building a biosignature data base (e.g. the proposed creation of an international Raman library). The library will be highly relevant for future space missions such as the search for life on Mars. The secondary scientific objective is to analyze to what extent terrestrial extremophiles are able to survive in space and to determine which interactions between biological samples and selected minerals (including terrestrial, Moon- and Mars analogs) can be observed under space and Mars-like conditions. In this context, the Moon will be an additional platform for performing similar experiments with negligible magnetic shielding and higher solar and galactic irradiation compared to LEO. Using the Moon as an additional astrobiological exposure platform to complement ongoing astrobiological LEO investigations could thus enhance the chances of detecting organic traces of life on Mars. We present a lunar lander mission with two related objectives: a lunar lander equipped with Raman and PanCam instruments which can analyze the lunar surface and survey an astrobiological exposure platform. This dual use of testing mission technology together with geo- and astrobiological analyses will significantly increase the science return, and support the human preparation objectives. It will provide knowledge about the Moon′s surface itself and, in addition, monitor the stability of life-markers, such as cells, cell components and pigments, in an extraterrestrial environment with much closer radiation properties to the surface of Mars. The combination of a Raman data base of these data together with data from LEO and space simulation experiments, will lead to further progress on the analysis and interpretation of data that we will obtain from future Moon and Mars exploration missions.
► We show connections between LEO investigations, Moon and Mars explorations. ► The relevance of data base collection about space resistant biosignatures. ► In situ measurements of exposed geo-bio-samples on a Lunar Lander ► BIOMEX as an example for astrobiological exposure experiments on the Moon. ► Combining Mineralogy and Biology to support the search for life on Mars.
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-PAM fluorometer) 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.
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