Survival of Methanogenic Archaea from Siberian Permafrost under Simulated Martian Thermal Conditions

Methanogenic archaea from Siberian permafrost complementary to the already well-studied methanogens from non-permafrost habitats were exposed to simulated Martian conditions. After 22 days of exposure to thermo-physical conditions at Martian low- and mid-latitudes up to 90% of methanogenic archaea from Siberian permafrost survived in pure cultures as well as in environmental samples. In contrast, only 0.3%–5.8% of reference organisms from non-permafrost habitats survived at these conditions. This suggests that methanogens from terrestrial permafrost seem to be remarkably resistant to Martian conditions. Our data also suggest that in scenario of subsurface lithoautotrophic life on Mars, methanogenic archaea from Siberian permafrost could be used as appropriate candidates for the microbial life on Mars.     

Survival of Microorganisms in a Simulated Martian Environment: I. Bacillus subtilis var. globigii

Survival of Bacillus subtilis var. globigii in a simulated Martian environment was demonstrated. Previous contact with the simulated Martian soil or atmosphere reduced germination or outgrowth of unheated spores, or both. Inoculation into simulated Martian soil and then flushing with a simulated Martian atmosphere were lethal to both vegetative cells and spores. After one diurnal temperature cycle (26 to -60 C), the majority of of cells present were spores. No further effect of the diurnal cycle on survival was noted in any of the experimental samples.     

Effect of Shadowing on Survival of Bacteria under Conditions Simulating the Martian Atmosphere and UV Radiation

Spacecraft-associated spores and four non-spore-forming bacterial isolates were prepared in Atacama Desert soil suspensions and tested both in solution and in a desiccated state to elucidate the shadowing effect of soil particulates on bacterial survival under simulated Martian atmospheric and UV irradiation conditions. All non-spore-forming cells that were prepared in nutrient-depleted, 0.2-μm-filtered desert soil (DSE) microcosms and desiccated for 75 days on aluminum died, whereas cells prepared similarly in 60-μm-filtered desert soil (DS) microcosms survived such conditions. Among the bacterial cells tested, Microbacterium schleiferi and Arthrobacter sp. exhibited elevated resistance to 254-nm UV irradiation (low-pressure Hg lamp), and their survival indices were comparable to those of DS- and DSE-associated Bacillus pumilus spores. Desiccated DSE-associated spores survived exposure to full Martian UV irradiation (200 to 400 nm) for 5 min and were only slightly affected by Martian atmospheric conditions in the absence of UV irradiation. Although prolonged UV irradiation (5 min to 12 h) killed substantial portions of the spores in DSE microcosms (~5- to 6-log reduction with Martian UV irradiation), dramatic survival of spores was apparent in DS-spore microcosms. The survival of soil-associated wild-type spores under Martian conditions could have repercussions for forward contamination of extraterrestrial environments, especially Mars.     

Survival of the Halophilic Archaeon Halovarius luteus after Desiccation,Simulated Martian UV Radiation and Vacuum in Comparison to Bacillus atrophaeus

Origins of Life and Evolution of Biospheres - Extraterrestrial environments influence the biochemistry of organisms through a variety of factors, including high levels of radiation and vacuum,...     

Survival of Microorganisms in a Simulated Martian Environment: II. Moisture and Oxygen Requirements for Germination of Bacillus cereus and Bacillus subtilis var. niger Spores1

The effects of moisture and oxygen concentration on germination of Bacillus cereus and B. subtilis var. niger spores were investigated in a simulated Martian environment. Less moisture was required for germination than for vegetative growth of both organisms. A daily freeze-thaw cycle lowered moisture requirements for spore germination and vegetative growth of both organisms, as compared with a constant 35 C environment. Oxygen had a synergistic effect by lowing the moisture requirements for vegetative growth, and possibly germination, of both organisms. Oxygen was not required for spore germination of either organism, but was required for vegetative growth of B. subtilis and for sporulation of both organisms.     

Survival of spacecraft-associated microorganisms under simulated martian UV irradiation

Spore-forming microbes recovered from spacecraft surfaces and assembly facilities were exposed to simulated Martian UV irradiation. The effects of UVA (315 to 400 nm), UVA+B (280 to 400 nm), and the full UV spectrum (200 to 400 nm) on the survival of microorganisms were studied at UV intensities expected to strike the surfaces of Mars. Microbial species isolated from the surfaces of several spacecraft, including Mars Odyssey, X-2000 (avionics), and the International Space Station, and their assembly facilities were identified using 16S rRNA gene sequencing. Forty-three Bacillus spore lines were screened, and 19 isolates showed resistance to UVC irradiation (200 to 280 nm) after exposure to 1,000 J m(-2) of UVC irradiation at 254 nm using a low-pressure mercury lamp. Spores of Bacillus species isolated from spacecraft-associated surfaces were more resistant than a standard dosimetric strain, Bacillus subtilis 168. In addition, the exposure time required for UVA+B irradiation to reduce the viable spore numbers by 90% was 35-fold longer than the exposure time required for the full UV spectrum to do this, confirming that UVC is the primary biocidal bandwidth. Among the Bacillus species tested, spores of a Bacillus pumilus strain showed the greatest resistance to all three UV bandwidths, as well as the total spectrum. The resistance to simulated Mars UV irradiation was strain specific; B. pumilus SAFR-032 exhibited greater resistance than all other strains tested. The isolation of organisms like B. pumilus SAFR-032 and the greater survival of this organism (sixfold) than of the standard dosimetric strains should be considered when the sanitation capabilities of UV irradiation are determined.     

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 of microorganisms in a simulated Martian environment

Studies were conducted to determine the effects of a simulated Martian environment on the survival of terrestrial microorganisms. Mariner IV data were utilized to establish the Martian model. Day/night cycling, temperature, humidity, pressure, atmospheric constituents and solar irradiation were controlled in a 3600 ft³ simulation chamber at the Boeing Kent Space Simulation Laboratory.Microorganisms used in this study included suspensions of:Bacillus subtilis var.niger spores, a psychrophilic sporeformer, and the organisms contained in a soil emulsion prepared from several soils. Aliquots of each suspension were placed on separate sterile stainless steel planchets, air dried, and positioned in 4 layers in sterile limonite. One-half of the samples placed on the surface received the total solar spectrum (0.44 earth solar constants); the remainder of the surface samples received the above treatment minus the ultraviolet (UV) portion of the spectrum. Subsurface samples were placed in limonite at depths of 0.5, 1.5 and 3 in.Survival data were obtained for chamber exposure periods of 2, 4, and 8 days. These data indicate that: (1) organisms exposed to the total solar spectrum did not survive, (2) a time dependent, 1 to 3 log, reduction in numbers occurred in the surface samples that received the solar spectrum minus UV, and (3) subsurface survival varied with depth and type or organism.     

Enhanced Photodegradation of PNP on Soil Surface under UV Irradiation with TiO2

Photodegradation of p-nitrophenol (PNP) on soil surface was investigated to explore the photochemical remediation of soil polluted by nitrophenols. Soil samples spiked with PNP were irradiated by UV light with and without the addition of TiO ₂ . The addition of 0.5–2 wt% TiO ₂ enhanced PNP photodegradation with approximately 1.36 times increase in apparent rate of PNP disappearance. Soil moisture, humic acid and soil pH were important factors influencing the rate of PNP photodegradation. Increase in soil moisture improved the degradation significantly, whereas humic acid reduced the degradation rate. Changes in soil pH resulted in different degradation rates, and higher degradation efficiencies were observed under alkaline condition.     

Survival of Microorganisms in Laundered Polyester-Cotton Sheeting

The effects of wash-water temperature, cold-water or regular detergent, wash-cycle design, drying, and drying temperature on survival of four microorganisms on polyester-cotton sheeting were examined. Escherichia coli T3 bacteriophage survived washing at 24, 35, 46, and 57 C, but not at 68 C. Serratia marcescens survived only the lowest three wash temperatures. Levels of residual Staphylococcus aureus were diminished at the highest two wash temperatures, but survival was substantial even at 68 C. Counts of Bacillus stearothermophilus spores were not altered appreciably by wash temperature. Type of detergent had no practical effect on observed counts. The regular wash cycle was significantly more efficient in removal of microorganisms than the permanent-press cycle. Counts, especially of the bacteriophage and the gramnegative bacterium, were decreased by drying; after drying, the effects of wash-water temperature on S. aureus and B. stearothermophilus were not significantly different. Microorganisms were transferred from inoculated to sterilized sheeting during laundering. The public health significance of these observations is discussed.     

Effect of Irradiation on Microorganisms in a Nuclear Reactor

The effects of irradiation in the JRR-1 (Japan Research Reactor No. 1, a homogeneous light water nuclear reactor; max. power, 50 KW) on microorganisms such as bacterial and fungal spores and yeast cells were investigated in comparison with those of ⁶⁰Co gamma radiation. As far as the lethal effect was concerned the dose rate of radiation in the experimental hole No. 16 of the JRR-1 was equivalent to 3.0×l0⁶~3.4×l0⁶ r/hr with ⁶⁰Co gamma radiation, and a ratio of the neutron effect to the gamma radiation effect on microorganisms in this hole was estimated to be approximately 3~5.4. The results different from those with gamma radiation were obtained in experiments such as post-NaCl treatment and spore germination. The considerable contribution of fast neutrons to the total biological effect of neutrons, in comparison with the thermal neutron effect, could be presumed from the microbiological experiments with the help of physical and chemical data. Morphological changes in post-irradiation growth were observed by means of phase contrast microscopy. No specific aftereffect was found.     

微生物在水环境中的存活和生长

在灭菌自来水模拟水体中,研究了7种细菌的存活和生长规律。Klebsiella pneumo-niae,Enterobacter aerogenes,Agrobacterium tumefatciens,在7天内平板计数降至0,而水体中镜检细菌总数(AODC)和活菌直接计数(DVC)结果无大变化,说明细菌已变成活的非可培养状态。Micrococcus,flavus 和 Streptococcus faecalis 的可培养菌数也可降至0。Pseudomonas sp.在48小时内由10~5降至10~2cfu/ml,随即升至10~6 cfu/ml 并持续到实验终了(41天)。Bacillus subtilis 在48小时平板计数降至10~2cfu/ml 并维持在该水平至实验结束(38天)。研究结果表明仅用涂布平板法检测多种细菌在水环境中的生存和分布是不合适的。     

Inactivation of Mycobacterium avium Complex by UV Irradiation

The effectiveness of two major UV technologies against a highly prevalent species of Mycobacterium avium complex was investigated. Our study indicates that M. avium is much more resistant to UV irradiation than most waterborne pathogens and that it is one of the rare microorganisms that are highly resistant to both chemical and UV disinfection in water.     

Efficacy of UV Irradiation in Inactivating Cryptosporidiumparvum Oocysts

To evaluate the effectiveness of UV irradiation in inactivating Cryptosporidium parvum oocysts, the animal infectivities and excystation abilities of oocysts that had been exposed to various UV doses were determined. Infectivity decreased exponentially as the UV dose increased, and the required dose for a 2-log₁₀ reduction in infectivity (99% inactivation) was approximately 1.0 mWs/cm² at 20°C. However, C. parvum oocysts exhibited high resistance to UV irradiation, requiring an extremely high dose of 230 mWs/cm² for a 2-log₁₀ reduction in excystation, which was used to assess viability. Moreover, the excystation ability exhibited only slight decreases at UV doses below 100 mWs/cm². Thus, UV treatment resulted in oocysts that were able to excyst but not infect. The effects of temperature and UV intensity on the UV dose requirement were also studied. The results showed that for every 10°C reduction in water temperature, the increase in the UV irradiation dose required for a 2-log₁₀ reduction in infectivity was only 7%, and for every 10-fold increase in intensity, the dose increase was only 8%. In addition, the potential of oocysts to recover infectivity and to repair UV-induced injury (pyrimidine dimers) in DNA by photoreactivation and dark repair was investigated. There was no recovery in infectivity following treatment by fluorescent-light irradiation or storage in darkness. In contrast, UV-induced pyrimidine dimers in the DNA were apparently repaired by both photoreactivation and dark repair, as determined by endonuclease-sensitive site assay. However, the recovery rate was different in each process. Given these results, the effects of UV irradiation on C. parvum oocysts as determined by animal infectivity can conclusively be considered irreversible.     

A Semi-Markovian Model for Cell Survival after Irradiation

To study the behaviour of a living cell exposed to radiations we investigate a stochastic model, employing for its analysis the theory of semi-Markov and Markov renewal processes. Four states of the cell namely, normal state, damaged state 1, damaged state 2 and altered state are defined and various characteristics of interest pertaining to the cell behaviour are studied.     

Meristems under Continuous Irradiation

Root tips of Vicia faba and Zea mays have been subjected tocontinuous irradiation from radium or cobalt-60 for long periodsat various dose rates. The rates of mitosis and the damage tothe chromosomes (assessed as percentages of cells with micronulei)have been measured in four regions of the meristems. In Zearates of mitosis are reduced under chronic irradiation, exceptin the quiescent centre, and the cap initials are particularlysensitive. In Vicia the main change in mitosis is that the quiescentcentre increases its rate, but at 12°C there is a slightstimulation of division all over the meristem. In Vicia increasingthe dose rate or lowering the temperature increases the nucleardamage. At 19° C there is an increase in damage with accumulateddose percell cycle, but the data at 12°C do not fall onthe 19°C curve, suggesting that there may be a temperatureeffect on damage other than that caused by changing the durationof the cell cycle. The differences in radiosensitivity betweenthe different regions of the meristem are due solely to differencesin the rates of mitosis of the cells.     

Factors Affecting High-Oxygen Survival of Heterotrophic Microorganisms from an Antarctic Lake

We sought to determine factors relating to the survival of heterotrophic microorganisms from the high-dissolved-oxygen (HDO) waters of Lake Hoare, Antarctica. This lake contains perpetual HDO about three times that of normal saturation (40 to 50 mg liter⁻¹). Five isolates, one yeast and four bacteria, were selected from Lake Hoare waters by growth with the membrane filter technique with oxygen added to yield dissolved concentrations 14 times that in situ, 175 mg liter⁻¹. One bacterial isolate was obtained from the microbial mat beneath the HDO waters. This organism was isolated at normal atmospheric oxygen saturation. The bacteria were gram-negative rods, motile, oxidase positive, catalase positive, and superoxide dismutase positive; they contained carotenoids. The planktonic isolates grew in media containing 10 mg of Trypticase soy (BBL Microbiology Systems)-peptone (2:1) liter⁻¹ but not at 10 g liter⁻¹. Under low-nutrient levels simulating Lake Hoare waters (10 mg liter⁻¹), two of the planktonic isolates tested were not inhibited by HDO. Growth inhibition by HDO increased as nutrient concentration was increased. A carotenoid-negative mutant of one isolate demonstrated a decreased growth rate, maximal cell density, and increased cell lysis in the death phase under HDO compared with the parent strain. The specific activity of superoxide dismutase was increased by HDO in four of the five bacterial isolates. The superoxide dismutase was of the manganese type on the basis of inhibition and electrophoretic studies. The bacterial isolates from Lake Hoare possess several adaptations which may aid their survival in the HDO waters, as well as protection due to the oligotrophic nature of the lake.