Stress response of methanogenic archaea from Siberian permafrost compared with methanogens from nonpermafrost habitats

We examined the survival potential of methanogenic archaea exposed to different environmental stress conditions such as low temperature (down to −78.5°C), high salinity (up to 6 M NaCl), starvation (up to 3 months), long-term freezing (up to 2 years), desiccation (up to 25 days) and oxygen exposure (up to 72 h). The experiments were conducted with methanogenic archaea from Siberian permafrost and were complemented by experiments on well-studied methanogens from nonpermafrost habitats. Our results indicate a high survival potential of a methanogenic archaeon from Siberian permafrost when exposed to the extreme conditions tested. In contrast, these stress conditions were lethal for methanogenic archaea isolated from nonpermafrost habitats. A better adaptation to stress was observed at a low temperature (4°C) compared with a higher one (28°C). Given the unique metabolism of methanogenic archaea in general and the long-term survival and high tolerance to extreme conditions of the methanogens investigated in this study, methanogenic archaea from permafrost should be considered as primary candidates for possible subsurface Martian life.     

Methanogenic communities in permafrost-affected soils of the Laptev Sea coast, Siberian Arctic, characterized by 16S rRNA gene fingerprints

Permafrost environments in the Arctic are characterized by extreme environmental conditions that demand a specific resistance from microorganisms to enable them to survive. In order to understand the carbon dynamics in the climate-sensitive Arctic permafrost environments, the activity and diversity of methanogenic communities were studied in three different permafrost soils of the Siberian Laptev Sea coast. The effect of temperature and the availability of methanogenic substrates on CH4 production was analysed. In addition, the diversity of methanogens was analysed by PCR with specific methanogenic primers and by denaturing gradient gel electrophoresis (DGGE) followed by sequencing of DGGE bands reamplified from the gel. Our results demonstrated methanogenesis with a distinct vertical profile in each investigated permafrost soil. The soils on Samoylov Island showed at least two optima of CH4 production activity, which indicated a shift in the methanogenic community from mesophilic to psychrotolerant methanogens with increasing soil depth. Furthermore, it was shown that CH4 production in permafrost soils is substrate-limited, although these soils are characterized by the accumulation of organic matter. Sequence analyses revealed a distinct diversity of methanogenic archaea affiliated to Methanomicrobiaceae, Methanosarcinaceae and Methanosaetaceae. However, a relationship between the activity and diversity of methanogens in permafrost soils could not be shown.     

Structure and Function of the A1A0-ATPases from Methanogenic Archaea

Recent molecular studies revealed nine to ten gene products involved infunction/assembly of the methanoarchaeal ATPase and unravel a closerelationship of the A₁A₀-ATPase and theV₁V₀-ATPase with respect to subunit composition and thestructure of individual subunits. Most interestingly, there is anastonishing variability in the size of the proteolipids in methanoar chaealA₁A₀-ATPases with six, four, or two transmembranehelices and a variable number of conserved protonizable groups per monomer.Despite the structural similarities the A₁A₀-ATPasediffers fundamentally from the V₁V₀-ATPase by itsability to synthesize ATP, a feature shared withF₁F₀-ATPases. The discovery of duplicated andtriplicated versions of the proteolipid in A₁A₀-ATPsynthases questions older views of the structural requirements for ATPsynthases versus ATP hydrolases and sheds new light on the evolutionof these secondary energy converters.     

Survival of Micromycetes and Actinobacteria under Conditions of Long-Term Natural Cryopreservation

Almost all of the investigated samples of the Arctic and Antarctic permafrost sediments of different genesis with ages from 5–10 thousand to 2–3 million years were found to contain viable micromycete and bacterial cells. The maximum amounts of viable cells of fungi (up to 10⁴CFU/g air-dried sample) and bacteria (up to 10⁷–10⁹CFU/g air-dried sample) were present in fine peaty sediment samples taken from different depths. The identified micromycetes belonged to more than 20 genera of the divisions Basidiomycota, Ascomycota, and Zygomycota, and some represented mitosporic fungi. Thawing the samples at 35 and 52°C allowed the number of detected fungal genera to be increased by more than 30%. Aerobic heterotrophic prokaryotes were dominated by coryneform, nocardioform, and spore-forming microorganisms of the order Actinomycetales.Analysis of the isolated fungi and actinomycetes showed that most of them originated from the microbial communities of ancient terrestrial biocenoses.     

Energy-Converting [NiFe] Hydrogenases from Archaea and Extremophiles: Ancestors of Complex I

[NiFe] hydrogenases are well-characterized enzymes that have a key function in the H2 metabolism of various microorganisms. In the recent years a subfamily of [NiFe] hydrogenases with unique properties has been identified. The members of this family form multisubunit membrane-bound enzyme complexes composed of at least four hydrophilic and two integral membrane proteins. These six conserved subunits, which built the core of these hydrogenases, have closely related counterparts in energy-conserving NADH:quinone oxidoreductases (complex I). However, the reaction catalyzed by these hydrogenases differs significantly from the reaction catalyzed by complex I. For some of these hydrogenases the physiological role is to catalyze the reduction of H+ with electrons derived from reduced ferredoxins or poly-ferredoxins. This exergonic reaction is coupled to energy conservation by means of electron-transport phosphorylation. Other members of this hydrogenase family mainly function to provide the cell with reduced ferredoxin with H2 as electron donor in a reaction driven by reverse electron transport. As complex I these hydrogenases function as ion pumps and have therefore been designated as energy-converting [NiFe] hydrogenases.     

tRNA-dependent Cysteine Biosynthetic Pathway Represents a Strategy to Increase Cysteine Contents by Preventing it from Thermal Degradation: Thermal Adaptation of Methanogenic Archaea Ancestor

Abstract

Although cysteine (Cys) is beneficial to stabilize protein structures, it is not prevalent in ther-mophiles. For instance, the Cys contents in most thermophilic archaea are only around 0.7%. However, methanogenic archaea, no matter thermophilic or not, contain relatively abundant Cys, which remains elusive for a long time. Recently, Klipcan et al. correlated this intriguing property of methanogenic archaea with their unique tRNA-dependent Cys biosynthetic pathway. But, the deep reasons underlying the correlation are ambiguous. Considering the facts that free Cys is thermally labile and the tRNA-dependent Cys biosynthesis avoids the use of free Cys, we speculate that the unique Cys biosynthetic pathway represents a strategy to increase Cys contents by preventing it from thermal degradation, which may be relevant to the thermal adaptation of methanogenic archaeza ancestor.     

Protection of Bacterial Spores in Space, a Contribution to the Discussion on Panspermia

Spores of Bacillus subtilis were exposed to space in theBIOPAN facility of the European Space Agency onboard of the Russian Earth-orbiting FOTON satellite. The spores were exposed either in dry layers without any protecting agent, or mixed withclay, red sandstone, Martian analogue soil or meteorite powder,in dry layers as well as in so-called `artificial meteorites', i.e. cubes filled with clay and spores in naturally occurring concentrations. After about 2 weeks in space, their survival was tested from the number of colony formers. Unprotected spores in layers open to space or behind a quartz window were completely or nearly completely inactivated (survival rates in most cases10^-6). The same low survival was obtained behind a thin layer of clay acting as an optical filter. The survival rate was increased by 5 orders of magnitude and more, if the spores in the dry layer were directly mixed with powder of clay,rock or meteorites, and up to 100% survival was reached in soilmixtures with spores comparable to the natural soil to spore ratio. These data confirm the deleterious effects of extraterrestrial solar UV radiation. Thin layers of clay, rock or meteorite are only successful in UV-shielding, if they are indirect contact with the spores. The data suggest that in a scenario of interplanetary transfer of life, small rock ejecta ofa few cm in diameter could be sufficiently large to protectbacterial spores against the intense insolation; however, micron-sized grains, as originally requested by Panspermia, may notprovide sufficient protection for spores to survive. The data arealso pertinent to search for life on Mars and planetaryprotection considerations for future missions to Mars.     

Survival of Microorganisms under the Extreme Conditions of the Atacama Desert

Spores of Bacillus subtilis, conidia of Aspergillus niger, versicolor and ochraceus andcells of Deinococcus radiodurans have been exposed in the dark at two locations (at about 23°S and 24°S) in the Atacama Desert for up to 15 months. B. subtilis spores (survival 15%) and A. niger conidia (survival 30%) outlived the other species. The survival of the conidiaand spores species was only slightly poorer than that of thecorresponding laboratory controls. However, the Deinococcus radiodurans cells did not survive the desertexposure, because they are readily inactivated at relativehumidities between 40 and 80% which typically occurduring desert nights. Cellular monolayers of the dry sporesand conidia have in addition been exposed to the full sunlight for up to several hours. The solar fluences causing 63% loss in viability (F₃₇-values) have been determined.These F₃₇-values are compared with those determined atother global locations such as Punta Arenas (53°S), Key Largo (25°N) or Mainz (50°N) during the same season. Thesolar UVB radiation kills even the most resistantmicroorganisms within a few hours due to DNA damages. Thedata are also discussed with respect to possible similaritiesbetween the climatic conditions of the recent Atacama Desertand the deserts of early Mars.     

Survival and Reproduction Potential of Philodina roseola (Ehrenberg) (Rotatoria,Bdelloida) under Various Temperature Conditions

Survival data, in addition to data on growth and reproduction rate, are necessary to estimate rotifer productivity under various thermal conditions. A method of individual culturing of Philodina roseola helped the authors to obtain data concerning length of life span and realisation of reproduction potential at different temperatures, ranging from 9 to 35 °C. The method also was helpful in revealing the causes of individual deaths. It is shown that at a temperature of 20 °C net reproduction rate (R₀) of Ph. roseola is maximum and is equal to reproduction potential of the individual. The peculiarity of Philodina ontogenetic reaction to temperature beyond optimum is the impairment of reproduction process.     

Effect of Dim and Bright Light Exposure on Some Immunological Parameters Measured under Thermal Neutral Conditions

This study assesses the effects of ambient light conditions, under a thermoneutral environment, on selected immunological parameters of 7 healthy young women (aged 19 to 22 yrs). Subjects entered the bioclimatic chamber at 11∶00 h, controlled at 26°C and 60% relative humidity, a “neutral climate”. They lead a well‐regulated life in the climatic chamber (pre‐condition) while exposed to dim (200 lux) or, on the next day, bright (5000 lux) light between 06∶00 to 12∶00 h. Just before the end of each period of light exposure, a blood sample was taken for later immunological assay of white blood cell count (WBC), phagocytosis, interferon‐γ (IFN‐γ), interleukin‐4 (IL‐4), CD69 T cells (CD69), CD4⁺CD25⁺ T cells (CD4⁺CD25⁺), and transforming growth factor‐β 1 (TGF‐β1). The results, when compared with the pre‐condition, were as follows: 1) CD69 and IFN‐γ increased during normal conditions without thermal stress under dim light; 2) WBC increased and IL‐4 decreased under bright light; 3) as shown by the highly significant decrease of TGF‐β1, the immune system was activated under bright light; 4) phagocytosis tended to increase under bright light exposure; 5) CD69 and IFN‐γ were significantly higher, and CD4⁺CD25⁺ tended to decrease under bright light; 6) phagocytosis tended to be lower and TGF‐β1 significantly higher under dim light, indicating a decline of immune system function. Taken together, this preliminary single time‐point sampling study infers that some parameters are activated (CD69) while others are attenuated (phagocytosis, TGF‐β1) according to the environmental light intensity, dim vs. bright, in women adhering to a standardized routine in the absence of thermal stress. These findings are discussed in terms of inhibition of the sympathetic and excitation of the parasympathetic nervous system under the influence of life‐style regularity and daytime bright light exposure.     

Life Cycle and Morphology of Bryopsidella ostreobiformis spec. nov. (Bryopsidaceae,Chlorophyta) from the Mediterranean,under Culture Conditions,with Comments on the Phylogeny of the Bryopsis/Derbesia Complex

Bryopsidella ostreobiformis sp. nov. is presented as the second species of the genus. The latter is amended to accomodate this new species. The derbesioid sporophyte is capable of producing three- to eight-rayed stellate propagules. The dioecious gametophyte is a heterotrichous thallus with branched, prostrate filaments and unbranched, erect ones, and does not resemble Bryopsis. The life cycle is distinctly diplohaplontic, with a diploid sporophyte and a haploid gametophyte. B. ostreobiformis is postulated as the starting point of a hypothetical evolutionary sequence of life histories in the Derbesia/Bryopsis complex.