Limits of Life and the Habitability of Mars: The ESA Space Experiment BIOMEX on the ISS

BIOMEX (BIOlogy and Mars EXperiment) is an ESA/Roscosmos space exposure experiment housed within the exposure facility EXPOSE-R2 outside the Zvezda module on the International Space Station (ISS). The design of the multiuser facility supports—among others—the BIOMEX investigations into the stability and level of degradation of space-exposed biosignatures such as pigments, secondary metabolites, and cell surfaces in contact with a terrestrial and Mars analog mineral environment. In parallel, analysis on the viability of the investigated organisms has provided relevant data for evaluation of the habitability of Mars, for the limits of life, and for the likelihood of an interplanetary transfer of life (theory of lithopanspermia). In this project, lichens, archaea, bacteria, cyanobacteria, snow/permafrost algae, meristematic black fungi, and bryophytes from alpine and polar habitats were embedded, grown, and cultured on a mixture of martian and lunar regolith analogs or other terrestrial minerals. The organisms and regolith analogs and terrestrial mineral mixtures were then exposed to space and to simulated Mars-like conditions by way of the EXPOSE-R2 facility. In this special issue, we present the first set of data obtained in reference to our investigation into the habitability of Mars and limits of life. This project was initiated and implemented by the BIOMEX group, an international and interdisciplinary consortium of 30 institutes in 12 countries on 3 continents. Preflight tests for sample selection, results from ground-based simulation experiments, and the space experiments themselves are presented and include a complete overview of the scientific processes required for this space experiment and postflight analysis. The presented BIOMEX concept could be scaled up to future exposure experiments on the Moon and will serve as a pretest in low Earth orbit

The responses of an anaerobic microorganism, Yersinia intermedia MASE-LG-1 to individual and combined simulated Martian stresses

The limits of life of aerobic microorganisms are well understood, but the responses of anaerobic microorganisms to individual and combined extreme stressors are less well known. Motivated by an interest in understanding the survivability of anaerobic microorganisms under Martian conditions, we investigated the responses of a new isolate, Yersinia intermedia MASE-LG-1 to individual and combined stresses associated with the Martian surface. This organism belongs to an adaptable and persistent genus of anaerobic microorganisms found in many environments worldwide. The effects of desiccation, low pressure, ionizing radiation, varying temperature, osmotic pressure, and oxidizing chemical compounds were investigated. The strain showed a high tolerance to desiccation, with a decline of survivability by four orders of magnitude during a storage time of 85 days. Exposure to X-rays resulted in dose-dependent inactivation for exposure up to 600 Gy while applied doses above 750 Gy led to complete inactivation. The effects of the combination of desiccation and irradiation were additive and the survivability was influenced by the order in which they were imposed. Ionizing irradiation and subsequent desiccation was more deleterious than vice versa. By contrast, the presence of perchlorates was not found to significantly affect the survival of the Yersinia strain after ionizing radiation. These data show that the organism has the capacity to survive and grow in physical and chemical stresses, imposed individually or in combination that are associated with Martian environment. Eventually it lost its viability showing that many of the most adaptable anaerobic organisms on Earth would be killed on Mars today

DNA double strand break repair in peripheral blood mononuclear cells from participants of head-down tilt bedrest studies

Introduction: Major limiting factors in human spaceflight are deleterious effects of reduced gravity and of space radiation exposure on health and performance. Radiationinduced cellular DNA damage, if not repaired or not correctly repaired, increases the risk of cancer and degenerative diseases. Likewise, reduced gravity may lead to musculoskeletal and cardiovascular deconditioning without appropriate countermeasures. We hypothesize that deconditioning could possibly hinder the recovery of cells from radiation damage. We aimed to develop a terrestrial ex vivo model to investigate cellular DNA repair while simulating microgravity effects using head-downtilt (HDT) bedrest during the Spaceflight-Associated Neuro-Ocular Syndrome Countermeasures (SANS-CM) studies. Methods: The SANS CM campaigns comprised three experimental phases: 1) a 14-days baseline data collection (BDC) phase (BDC-14 through BDC-1); 2) 30 days of 6° HDT bedrest phase (HDT1 through HDT30); and 3) a 14- days recovery (R+) phase (R+0 through R+13). Twelve participants were enrolled in each campaign. Blood samples were obtained from the subjects 14 days before the bedrest (BDC-14), 10 and 28 days into head-down-tilt bedrest (HDT-10 and HDT-28) and after 10 days of recovery (R+10). Peripheral blood mononuclear cells (PBMC) were isolated by density gradient centrifugation using Greiner LeucosepTM tubes. We studied the ex vivo induction and repair of DNA double strand breaks, for which the cells were exposed to 1 and 4 Gy of X-rays and harvested after 0.5, 1, 2, 4 and 24 h after irradiation. DNA double strand breaks were detected via immunofluorescence staining of gamma-H2AX that was quantified using flow cytometry. Results: The results for gamma-H2AX fluorescence intensity and the percentage of cells with unrepaired DNA reached a peak value after 2 h of X-rays irradiation and was greatly reduced after 24 h. For all blood collection time-points during the study, BDC-14, HDT-10, HDT-28 and R+10, the gamma-H2AX fluorescence intensity did not differ significantly. Furthermore, there was no significant interpersonal variance of DNA double strand break repair capacity. Conclusion: DNA double strand break repair activity in PBMC remained unaffected by one month of HDT bedrest, suggesting that the physical deconditioning does not modulate DNA repair capacity. Acknowledgement: The study was funded by the National Aeronautics and Space Administration (NASA) and the German Aerospace Center, and performed at the :envihab research facility of the DLR Institute of Aerospace Medicine. The authors wish to gratefully acknowledge the bedrest participants who volunteered their time, without whom this project would not have been possible. We also thank the SANS-CM study staffs for their dedicated work and tireless effort

DNA double strand break repair in peripheral blood mononuclear cells from participants of head-down tilt bedrest studies

Introduction: Major limiting factors in human spaceflight are deleterious effects of reduced gravity and of space radiation exposure on health and performance. Radiationinduced cellular DNA damage, if not repaired or not correctly repaired, increases the risk of cancer and degenerative diseases. Likewise, reduced gravity may lead to musculoskeletal and cardiovascular deconditioning without appropriate countermeasures. We hypothesize that deconditioning could possibly hinder the recovery of cells from radiation damage. We aimed to develop a terrestrial ex vivo model to investigate cellular DNA repair while simulating microgravity effects using head-downtilt (HDT) bedrest during the Spaceflight-Associated Neuro-Ocular Syndrome Countermeasures (SANS-CM) studies. Methods: The SANS CM campaigns comprised three experimental phases: 1) a 14-days baseline data collection (BDC) phase (BDC-14 through BDC-1); 2) 30 days of 6° HDT bedrest phase (HDT1 through HDT30); and 3) a 14- days recovery (R+) phase (R+0 through R+13). Twelve participants were enrolled in each campaign. Blood samples were obtained from the subjects 14 days before the bedrest (BDC-14), 10 and 28 days into head-down-tilt bedrest (HDT-10 and HDT-28) and after 10 days of recovery (R+10). Peripheral blood mononuclear cells (PBMC) were isolated by density gradient centrifugation using Greiner LeucosepTM tubes. We studied the ex vivo induction and repair of DNA double strand breaks, for which the cells were exposed to 1 and 4 Gy of X-rays and harvested after 0.5, 1, 2, 4 and 24 h after irradiation. DNA double strand breaks were detected via immunofluorescence staining of gamma-H2AX that was quantified using flow cytometry. Results: The results for gamma-H2AX fluorescence intensity and the percentage of cells with unrepaired DNA reached a peak value after 2 h of X-rays irradiation and was greatly reduced after 24 h. For all blood collection time-points during the study, BDC-14, HDT-10, HDT-28 and R+10, the gamma-H2AX fluorescence intensity did not differ significantly. Furthermore, there was no significant interpersonal variance of DNA double strand break repair capacity. Conclusion: DNA double strand break repair activity in PBMC remained unaffected by one month of HDT bedrest, suggesting that the physical deconditioning does not modulate DNA repair capacity. Acknowledgement: The study was funded by the National Aeronautics and Space Administration (NASA) and the German Aerospace Center, and performed at the :envihab research facility of the DLR Institute of Aerospace Medicine. The authors wish to gratefully acknowledge the bedrest participants who volunteered their time, without whom this project would not have been possible. We also thank the SANS-CM study staffs for their dedicated work and tireless effort

INFLUENCE OF HEAD-DOWN TILT BEDREST ON DNA REPAIR CAPACITY

INTRODUCTION Major limiting factors in human spaceflight are the deleterious effects of reduced gravity and space radiation exposure on health and performance. Radiation-induced cellular DNA damage, if not repaired or not correctly repaired, increases the risk of cancer and degenerative diseases. Likewise, without appropriate countermeasures, reduced gravity will lead to musculoskeletal and cardiovascular deconditioning. We hypothesized that deconditioning per se would hinder the recovery of cells from radiation damage. We developed a terrestrial ex vivo model to investigate cellular DNA repair while simulating microgravity effects using head-down-tilt (HDT) bedrest during the Spaceflight-Associated Neuro-Ocular Syndrome Countermeasures (SANS-CM) study. METHODS Each of the four SANS CM campaigns comprised three experimental phases: 1) a 14-day baseline data collection (BDC) phase (BDC-14 through BDC-1); 2) a 30-day 6° HDT bedrest phase (HDT1 through HDT30); and 3) a 14-day recovery (R+) phase (R+0 through R+13). Twelve participants were enrolled in each campaign. Blood samples were obtained from the subjects 14 days before the bedrest (BDC-14), 10 and 28 days into head-down-tilt bedrest (HDT10 and HDT28), and after 10 days of recovery (R+10). Peripheral blood mononuclear cells (PBMC) were isolated by density gradient centrifugation using Greiner LeucosepTM tubes. We studied the ex vivo induction and repair of DNA double strand breaks, for which the cells were exposed to 1 and 4 Gy of X-rays. The cells were then harvested 0.5, 1, 2, 4, and 24 h after irradiation. DNA double strand breaks were detected via immunofluorescence staining of γH2AX that was quantified using flow cytometry. RESULTS The results for γH2AX fluorescence intensity and the percentage of cells with unrepaired DNA reached a peak value after 2 h of X-rays irradiation and was greatly reduced after 24 h. For all blood collection time-points during the study, the γH2AX fluorescence intensity did not differ significantly. Furthermore, there was no significant interpersonal variance of DNA double strand break repair capacity. CONCLUSION DNA double strand break repair activity in PBMC remained unaffected by 30 days of HDT bedrest, suggesting that physiological deconditioning likely does not modulate DNA repair capacity. ACKNOWLEDGEMENT The study was funded by the National Aeronautics and Space Administration (NASA) and the German Aerospace Center (DLR), and performed at the :envihab research facility of the DLR Institute of Aerospace Medicine. The authors wish to gratefully acknowledge the bedrest participants who volunteered their time, without whom this project would not have been possible. We also thank the SANS CM study staff for their dedicated work and tireless effort