Gerda Horneck

Responses of Bacillus subtilis Spores to Space Environment: Results from Experiments in Space

Onboard of several spacecrafts (Apollo 16, Spacelab 1, LDEF), spores ofBacillus subtilis were exposed to selected parameters of space, such as space vacuum, different spectral ranges of solar UV-radiation and cosmic rays, applied separately or in combination, and we have studied their survival and genetic changes after retrieval. The spores survive extended periods of time in space — up to several years —, if protected against the high influx of solar UV-radiation. Water desorption caused by the space vacuum leads to structural changes of the DNA; the consequences are an increased mutation frequency and altered photobiological properties of the spores. UV-effects, such as killing and mutagenesis, are augmented, if the spores are in space vacuum during irradiation. Vacuum-specific photoproducts which are different from the ‘spore photoproduct’ may cause the synergistic response of spores to the simultaneous action of UV and vacuum. The experiments provide an experimental test of certain steps of the panspermia hypothesis.

Role of DNA Repair by Nonhomologous-End Joining in Bacillus subtilis Spore Resistance to Extreme Dryness, Mono- and Polychromatic UV, and Ionizing Radiation

The role of DNA repair by nonhomologous-end joining (NHEJ) in spore resistance to UV, ionizing radiation, and ultrahigh vacuum was studied in wild-type and DNA repair mutants (recA, splB, ykoU, ykoV, and ykoU ykoV mutants) of Bacillus subtilis. NHEJ-defective spores with mutations in ykoU, ykoV, and ykoU ykoV were significantly more sensitive to UV, ionizing radiation, and ultrahigh vacuum than wild-type spores, indicating that NHEJ provides an important pathway during spore germination for repair of DNA double-strand breaks.

Microbial rock inhabitants survive hypervelocity impacts on Mars-like host planets: First phase of lithopanspermia experimentally tested

The scenario of lithopanspermia describes the viable transport of microorganisms via meteorites. To test the first step of lithopanspermia, i.e., the impact ejection from a planet, systematic shock recovery experiments within a pressure range observed in martian meteorites (5-50 GPa) were performed with dry layers of microorganisms (spores of Bacillus subtilis, cells of the endolithic cyanobacterium Chroococcidiopsis, and thalli and ascocarps of the lichen Xanthoria elegans) sandwiched between gabbro discs (martian analogue rock). Actual shock pressures were determined by refractive index measurements and Raman spectroscopy, and shock temperature profiles were calculated. Pressure-effect curves were constructed for survival of B. subtilis spores and Chroococcidiopsis cells from the number of colony-forming units, and for vitality of the photobiont and mycobiont of Xanthoria elegans from confocal laser scanning microscopy after live/dead staining (FUN-I). A vital launch window for the transport of rock-colonizing microorganisms from a Mars-like planet was inferred, which encompasses shock pressures in the range of 5 to about 40 GPa for the bacterial endospores and the lichens, and a more limited shock pressure range for the cyanobacterium (from 5-10 GPa). The results support concepts of viable impact ejections from Mars-like planets and the possibility of reseeding early Earth after asteroid cataclysms.

A BIOFILM USED AS ULTRAVIOLET‐DOSIMETER

Abstract— A UV‐dosimeter has been developed for routine measurements which mainly weights the various components of the spectrum in relation to their damaging effects on a microorganism. For this purpose a biofilm was constructed, comprising dried spores of Bacillus subtilis (wild‐type or DNA repair defective strain), immobilized on transparent polyester plastic sheets. After irradiation, the biofilm was incubated in a growth medium. The proteins, synthesized by the immobilized microorganisms after spore germination and several cell divisions, were stained and determined by photometry, giving a measure of the biological activity. The ”biologically effective dose“ was determined from a calibration curve. It reflects the dose equivalent to that of the calibration source producing the same effect.

Survival of Rock-Colonizing Organisms After 1.5 Years in Outer Space

Cryptoendolithic microbial communities and epilithic lichens have been considered as appropriate candidates for the scenario of lithopanspermia, which proposes a natural interplanetary exchange of organisms by means of rocks that have been impact ejected from their planet of origin. So far, the hardiness of these terrestrial organisms in the severe and hostile conditions of space has not been tested over extended periods of time. A first long-term (1.5 years) exposure experiment in space was performed with a variety of rock-colonizing eukaryotic organisms at the International Space Station on board the European EXPOSE-E facility. Organisms were selected that are especially adapted to cope with the environmental extremes of their natural habitats. It was found that some-but not all-of those most robust microbial communities from extremely hostile regions on Earth are also partially resistant to the even more hostile environment of outer space, including high vacuum, temperature fluctuation, the full spectrum of extraterrestrial solar electromagnetic radiation, and cosmic ionizing radiation. Although the reported experimental period of 1.5 years in space is not comparable with the time spans of thousands or millions of years believed to be required for lithopanspermia, our data provide first evidence of the differential hardiness of cryptoendolithic communities in space.

Localisation and distance between ABL and BCR genes in interphase nuclei of bone marrow cells of control donors and patients with chronic myeloid leukaemia.

Quantitative measurements of the nuclear localisation of the ABL and BCR genes and the distance between them were performed in randomly oriented bone marrow cells of control donors and patients with chronic myeloid leukaemia (CML). Most ABL and BCR genes (75%) are located at a distance of 20–65% of the local radius from the nuclear centre to the nuclear membrane. A chimeric BCR-ABL gene located on a derivative chromosome 22 resulting from t(9;22)(q34;q11) [the so-called Philadelphia (Ph) chromosome] as well as the intact ABL and BCR genes of patients suffering from chronic myeloid leukaemia are also located mostly in this region, which has a mean thickness of 2 μm in bone marrow cells. We have not found any significant differences in the location of the two genes in the G1 and G2 phases of the cell cycle, nor between bone marrow cells and stimulated lymphocytes. Irradiation of lymphocytes with a dose of 5 Gy of γ-rays results in a shift of both genes to the central region of the nucleus (0–20% of the radius distant from the nuclear centre) in about 15% of the cells. The minimum distance between one ABL and one BCR gene is less than 1 μm in 47.5% of bone marrow cells of control donors. Such a small distance is found between homologous ABL and between homologous BCR genes in only 8.1% and 8.4% of cells, respectively. It is possible that the relative closeness of nonhomologous ABL and BCR genes in interphase nuclei of bone marrow cells could facilitate translocation between these genes. In 16.4% of bone marrow cells one ABL and one BCR gene are juxtaposed (the distance between them varies from 0–0.5 μm) and simulate the Ph chromosome. This juxtaposition is the result of the projection of two genes located one above another into a plane, as follows from the probability calculation.

QUANTIFICATION OF THE BIOLOGICAL EFFECTIVENESS OF ENVIRONMENTAL UV RADIATION

Abstract To determine the impact of environmental UV radiation on the critical processes of our biosphere demands accurate and reliable monitoring systems that weight the spectral irradiance according to the biological responses under consideration. The need for the biological weighting of solar UV irradiance derives from the highly wavelength-specific absorption characteristics of atmospheric ozone and the wavelength specificity of the biological action spectra in the UVB range. The degree to which the biological effectiveness of solar UV radiation increase with stratospheric ozone depletion is determined by the shape of the action spectrum of the biological phenomenon under consideration. In principle, three different approaches for quantifying biologically effective solar irradiance are available: (1) weighted spectroradiometry where the biologically weighted radiometric quantities are derived from spectral data by multiplication with an action spectrum of a relevant photobiological reaction, e.g. erythema formation, DNA damage, skin cancer or reduced productivity of terrestrial plants and aquatic ecosystems; (2) wavelength-integrating chemical or physical dosimetric systems with spectral sensitivities similar to a biological response curve; (3) biological dosimeters that weight directly the incident UV components of sunlight in relation to the effectiveness of the different wavelengths and the interactions between them. In most cases, simple biological dosimeters are applied, such as bacteria, bacteriophages or biomolecules. Induction rates for lethality, mutagenesis or photoproduct formation are used, which reflect directly the UV sensitivity of DNA. Biological dosimeters are potentially reliable field dosimeters for measuring the integrated biologically effective irradiance for key targets, provided that a direct intercalibration with spectroradiometric-based measurements is applied.

Radiobiological experiments in space: A review☆☆☆

Abstract Of the various fields of radiation biology in space, comprising (1) radiation detection and measurement; (2) studies on the biological response to radiation in space; (3) the impact of spaceflight environment on radiation effects; and (4) radiation protection efforts, this paper deals mainly with results from space experiments on the biological effects of cosmic ray HZE particles and on their potential interactions with the microgravity environment. So far, mainly with resting systems, such as viruses, bacterial spores, plant seeds or shrimp cysts, as well as in a few embryonic systems, methods have been applied to trace injuries to the passage of a single HZE particle of cosmic radiation. Most effects point to damage to the genetic material, such as mutations, tumour induction, chromosomal aberrations, cell inactivation, or development anomalies. Using higher organisms, including mammals, a few attempts have been made to identify tissue damage along the passage of single HZE particles, such as microscopically visible injury in brain or eyes, or the light flash sensation. The latter, correlated with orbital parameters, showed highest frequency during the passage of the South Atlantic Anomaly. To study potential interactions of ionizing radiation with microgravity, either additional irradiation was applied, pre-, in-, or post-flight, or a 1 g reference centrifuge was utilized in combination with methods of particle effect correlation. Especially in embryonic systems, synergistic interactions were observed in producing mutations or anomalies with high frequency. It is assumed that, among other mechanisms, microgravity might interfere with the function of DNA repair systems. On the basis of the results obtained on the biological effectiveness of radiation in space and in view of upcoming space activities with an increasing number of manned missions, perspectives are given for future experimental approaches in space radiation biology.

Resistance of Antarctic black fungi and cryptoendolithic communities to simulated space and Martian conditions.

Dried colonies of the Antarctic rock-inhabiting meristematic fungi Cryomyces antarcticus CCFEE 515, CCFEE 534 and C. minteri CCFEE 5187, as well as fragments of rocks colonized by the Antarctic cryptoendolithic community, were exposed to a set of ground-based experiment verification tests (EVTs) at the German Aerospace Center (DLR, Köln, Germany). These were carried out to test the tolerance of these organisms in view of their possible exposure to space conditions outside of the International Space Station (ISS). Tests included single or combined simulated space and Martian conditions. Responses were analysed both by cultural and microscopic methods. Thereby, colony formation capacities were measured and the cellular viability was assessed using live/dead dyes FUN 1 and SYTOX Green. The results clearly suggest a general good resistance of all the samples investigated. C. minteri CCFEE 5187, C. antarcticus CCFEE 515 and colonized rocks were selected as suitable candidates to withstand space flight and long-term permanence in space on the ISS in the framework of the LIchens and Fungi Experiments (LIFE programme, European Space Agency).

The History of the UV Radiation Climate of the Earth—Theoretical and Space-based Observations¶

In the Archean era (3.8–2.5 Ga ago) the Earth probably lacked a protective ozone column. Using data obtained in the Earths orbit on the inactivation of Bacillus subtilis spores we quantitatively estimate the potential biological effects of such an environment. We combine this practical data with theoretical calculations to propose a history of the potential UV stress on the surface of the Earth over time. The data suggest that an effective ozone column was established at a pO2 of ∼5 × 10−3 present atmospheric level. The improvement in the UV environment on the early Proterozoic Earth might have been a much more rapid event than has previously been supposed, with DNA damage rates dropping by two orders of magnitude in the space of just a few tens of millions of years. We postulate that a coupling between reduced UV stress and increased pO2 production could have contributed toward a positive feedback in the production of ozone in the early Proterozoic atmosphere. This would contribute to the apparent rapidity of the oxidation event. The data provide an evolutionary perspective on present‐day Antarctic ozone depletion.