Carotenoids are promising targets in our quest to search for life on Mars due to their biogenic origin and easy detection by Raman spectroscopy, especially with a 532 nm excitation thanks to ...resonance effects. Ionizing radiations reaching the surface and subsurface of Mars are however detrimental for the long-term preservation of biomolecules. We show here that desiccation can protect carotenoid Raman signatures in the desert cyanobacterium
sp. CCMEE 029 even after high-dose gamma irradiation. Indeed, while the height of the carotenoids Raman peaks was considerably reduced in hydrated cells exposed to gamma irradiation, it remained stable in dried cells irradiated with the highest tested dose of 113 kGy of gamma rays, losing only 15-20% of its non-irradiated intensity. Interestingly, even though the carotenoid Raman signal of hydrated cells lost 90% of its non-irradiated intensity, it was still detectable after exposure to 113 kGy of gamma rays. These results add insights into the preservation potential and detectability limit of carotenoid-like molecules on Mars over a prolonged period of time and are crucial in supporting future missions carrying Raman spectrometers to Mars' surface.
To study the role of different DNA repair genes in the resistance of Deinococcus radiodurans to mono- and polychromatic UV radiation, wild-type strain and knockout mutants in RecA, PprA, and IrrE of ...D. radiodurans were irradiated with UV-C (254 nm), UV-(A + B) (280-400 nm) and UV-A (315-400 nm) radiation, and survival was monitored. The strain deficient in recA was highly sensitive to UV-C radiation compared to the wild-type, but showed no loss of resistance against irradiation with UV-(A + B) and UV-A, while pprA and irrE-deficient strains exhibited elevated sensitivity to UV-A and UV-(A + B) radiation. These results suggest that the repair of DNA double-strand breaks is essential after treatment with highly energetic UV-C radiation, whereas protection from oxidative stress may play a greater role in resistance to environmentally relevant UV radiation.
Mutations in the RNA polymerase β-subunit gene
rpoB
causing resistance to rifampicin (Rif
R
) in
Bacillus subtilis
were previously shown to lead to alterations in the expression of a number of global ...phenotypes known to be under transcriptional control. To better understand the influence of
rpoB
mutations on sporulation and spore resistance to heat and chemicals, cells and spores of the wild-type and twelve distinct congenic Rif
R
mutant strains of
B. subtilis
were tested. Different levels of glucose catabolite repression during sporulation and spore resistance to heat and chemicals were observed in the Rif
R
mutants, indicating the important role played by the RNA polymerase β-subunit, not only in the catalytic aspect of transcription, but also in the initiation of sporulation and in the spore resistance properties of
B. subtilis
.
Extremophiles are optimal models in experimentally addressing questions about the effects of cosmic radiation on biological systems. The resistance to high charge energy (HZE) particles, and helium ...(He) ions and iron (Fe) ions (LET at 2.2 and 200 keV/µm, respectively, until 1000 Gy), of spores from two thermophiles, Bacillushorneckiae SBP3 and Bacilluslicheniformis T14, and two psychrotolerants, Bacillus sp. A34 and A43, was investigated. Spores survived He irradiation better, whereas they were more sensitive to Fe irradiation (until 500 Gy), with spores from thermophiles being more resistant to irradiations than psychrotolerants. The survived spores showed different germination kinetics, depending on the type/dose of irradiation and the germinant used. After exposure to He 1000 Gy, D-glucose increased the lag time of thermophilic spores and induced germination of psychrotolerants, whereas L-alanine and L-valine increased the germination efficiency, except alanine for A43. FTIR spectra showed important modifications to the structural components of spores after Fe irradiation at 250 Gy, which could explain the block in spore germination, whereas minor changes were observed after He radiation that could be related to the increased permeability of the inner membranes and alterations of receptor complex structures. Our results give new insights on HZE resistance of extremophiles that are useful in different contexts, including astrobiology.
The habitability of Mars is determined by the physical and chemical environment. The effect of low water availability, temperature, low atmospheric pressure and strong UV radiation has been ...extensively studied in relation to the survival of microorganisms. In addition to these stress factors, it was recently found that silicates exposed to simulated saltation in a Mars-like atmosphere can lead to a production of reactive oxygen species. Here, we have investigated the stress effect induced by quartz and basalt abraded in Mars-like atmospheres by examining the survivability of the three microbial model organisms
, and
upon exposure to the abraded silicates. We found that abraded basalt that had not been in contact with oxygen after abrasion killed more than 99% of the vegetative cells while endospores were largely unaffected. Exposure of the basalt samples to oxygen after abrasion led to a significant reduction in the stress effect. Abraded quartz was generally less toxic than abraded basalt. We suggest that the stress effect of abraded silicates may be caused by a production of reactive oxygen species and enhanced by transition metal ions in the basalt leading to hydroxyl radicals through Fenton-like reactions. The low survivability of the usually highly resistant
indicates that the effect of abraded silicates, as is ubiquitous on the Martian surface, would limit the habitability of Mars as well as the risk of forward contamination. Furthermore, the reactivity of abraded silicates could have implications for future manned missions, although the lower effect of abraded silicates exposed to oxygen suggests that the effects would be reduced in human habitats.
The modern concept of the evolution of Mars assumes that life could potentially have originated on the planet Mars, possibly during the end of the late heavy bombardment, and could then be ...transferred to other planets. Since then, physical and chemical conditions on Mars changed and now strongly limit the presence of terrestrial-like life forms. These adverse conditions include scarcity of liquid water (although brine solutions may exist), low temperature and atmospheric pressure, and cosmic radiation. Ionizing radiation is very important among these life-constraining factors because it damages DNA and other cellular components, particularly in liquid conditions where radiation-induced reactive oxidants diffuse freely. Here, we investigated the impact of high doses (up to 2 kGy) of densely-ionizing (197.6 keV/µm), space-relevant iron ions (corresponding on the irradiation that reach the uppermost layer of the Mars subsurface) on the survival of an extremophilic terrestrial organism—Cryomyces antarcticus—in liquid medium and under atmospheric conditions, through different techniques. Results showed that it survived in a metabolically active state when subjected to high doses of Fe ions and was able to repair eventual DNA damages. It implies that some terrestrial life forms can withstand prolonged exposure to space-relevant ion radiation.
Bacterial spores of
Bacillus subtilis were used as a model system to study the effects of ionizing radiation on the survivability of spores uncovered and covered with artificial martian regolith. ...Spore survival after X-ray exposure was mainly depending on the role of non-homologous end-joining (NHEJ) as the major DNA double-strand break repair pathway during germination, the involvement of major small, acid-soluble spore proteins (SASP) as DNA radioprotectants and the coverage by martian regolith, whereas spores covered with martian regolith were significantly more sensitive to X-rays than uncovered spores, which is mainly due to the interaction of X-rays with artificial martian regolith resulting in the formation of secondary electrons and reactive oxygen species.
As part of the PROTECT experiment of the EXPOSE-E mission on board the International Space Station (ISS), the mutagenic efficiency of space was studied in spores of Bacillus subtilis 168. After 1.5 ...years' exposure to selected parameters of outer space or simulated martian conditions, the rates of induced mutations to rifampicin resistance (Rif(R)) and sporulation deficiency (Spo(-)) were quantified. In all flight samples, both mutations, Rif(R) and Spo(-), were induced and their rates increased by several orders of magnitude. Extraterrestrial solar UV radiation (>110 nm) as well as simulated martian UV radiation (>200 nm) led to the most pronounced increase (up to nearly 4 orders of magnitude); however, mutations were also induced in flight samples shielded from insolation, which were exposed to the same conditions except solar irradiation. Nucleotide sequencing located the Rif(R) mutations in the rpoB gene encoding the β-subunit of RNA polymerase. Mutations isolated from flight and parallel mission ground reference (MGR) samples were exclusively localized to Cluster I. The 21 Rif(R) mutations isolated from the flight experiment showed all a C to T transition and were all localized to one hotspot: H482Y. In mutants isolated from the MGR, the spectrum was wider with predicted amino acid changes at residues Q469K/L/R, H482D/P/R/Y, and S487L. The data show the unique mutagenic power of space and martian surface conditions as a consequence of DNA injuries induced by solar UV radiation and space vacuum or the low pressure of Mars.
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.
In local Principal Component Analysis (PCA), a distribution is approximated by multiple units, each representing a local region by a hyper-ellipsoid obtained through PCA. We present an extension for ...local PCA which adaptively adjusts both the learning rate of each unit and the potential function which guides the competition between the local units. Our local PCA method is an online neural network method where unit centers and shapes are modified after the presentation of each data point. For several benchmark distributions, we demonstrate that our method improves the overall quality of clustering, especially for high-dimensional distributions where many conventional methods do not perform satisfactorily. Our online method is also well suited for the processing of streaming data: The two adaptive mechanisms lead to a quick reorganization of the clustering when the underlying distribution changes.
•Highly accurate clustering results in high-dimensional data spaces.•Adaptive learning rate to learn dynamic data distributions.•Adaptive potential function to continuously learn all local models.•Systematic analysis of learning rule combinations for local PCA.
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