scholarly journals Effects of Radiation Intensity, Mineral Matrix, and Pre-Irradiation on the Bacterial Resistance to Gamma Irradiation under Low Temperature Conditions

2021 ◽  
Vol 9 (1) ◽  
pp. 198
Author(s):  
Vladimir S. Cheptsov ◽  
Andrey A. Belov ◽  
Elena A. Vorobyova ◽  
Anatoli K. Pavlov ◽  
Vladimir N. Lomasov
Keyword(s):  
Low Temperature ◽  
Gamma Radiation ◽  
Radiation Intensity ◽  
Bacterial Resistance ◽  
Great Influence ◽  
Experimental Conditions ◽  
Temperature Conditions ◽  
Solid Media ◽  
Space Objects ◽  
Mineral Matrix

Ionizing radiation is one of the main factors limiting the survival of microorganisms in extraterrestrial conditions. The survivability of microorganisms under irradiation depends significantly on the conditions, in which the irradiation occurs. In particular, temperature, pressure, oxygen and water concentrations are of great influence. However, the influence of factors such as the radiation intensity (in low-temperature conditions) and the type of mineral matrix, in which microorganisms are located, has been practically unstudied. It has been shown that the radioresistance of bacteria can increase after their exposure to sublethal doses and subsequent repair of damage under favorable conditions, however, such studies are also few and the influence of other factors of extraterrestrial space (temperature, pressure) was not studied in them. The viability of bacteria Arthrobacter polychromogenes, Kocuria rosea and Xanthomonas sp. after irradiation with gamma radiation at a dose of 1 kGy under conditions of low pressure (1 Torr) and low temperature (−50 °C) at different radiation intensities (4 vs. 0.8 kGy/h) with immobilization of bacteria on various mineral matrices (montmorillonite vs. analogue of lunar dust) has been studied. Native, previously non-irradiated strains, and strains that were previously irradiated with gamma radiation and subjected to 10 passages of cultivation on solid media were irradiated. The number of survived cells was determined by culturing on a solid medium. It has been shown that the radioresistance of bacteria depends significantly on the type of mineral matrix, on which they are immobilized, wherein montmorillonite contributes to an increased survivability in comparison with a silicate matrix. Survivability of the studied bacteria was found to increase with decreasing radiation intensity, despite the impossibility of active reparation processes under experimental conditions. Considering the low intensity of radiation on various space objects in comparison with radiobiological experiments, this suggests a longer preservation of the viable microorganisms outside the Earth than is commonly believed. An increase in bacterial radioresistance was revealed even after one cycle of irradiation of the strains and their subsequent cultivation under favourable conditions. This indicates the possibility of hypothetical microorganisms on Mars increasing their radioresistance.

Zur Strahleninaktivierung von Ribonuclease

1968 ◽  
Vol 23 (7) ◽  
pp. 934-943 ◽  
Author(s):  
Horst Jung ◽  
Helga Schüssler
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Low Temperature ◽  
Gamma Radiation ◽  
Enzymatic Activity ◽  
Amino Acid Residue ◽  
Atomic Hydrogen ◽  
Active Components ◽  
Experimental Conditions ◽  
Elution Pattern

Dry ribonuclease was irradiated with 60Co gamma radiation in vacuo, under oxygen atmosphere, and at 77 °K. By chromatography on Sephadex G-50 active ribonuclease was separated from inactive radiation products. From the elution pattern and by ultracentrifugation it was shown that mainly unfolded dimers are formed by gamma irradiation of dry ribonuclease. Amino acid analysis of these various products shows that in all components cystine, methionine, tyrosine, phenylalanine, lysine, and histidine are destroyed with increasing dose whereas glycine shows a small increase. Thus, in ribonuclease irradiated in the dry state the same amino acids are changed as was found after irradiation in aqueous solutions. The radiosensitivity of dry ribonuclease shows an increase by the presence of oxygen of about 2 and a decrease at low temperature in vacuo of about 5. The same factors were also found for the alteration of amino acids, which means that under various experimental conditions amino acid destruction is proportional to loss of enzymatic activity of ribonuclease. The observed selectivity of amino acid destruction may be explained by energy migration or by the attack of atomic hydrogen liberated at random from the molecule. The total number of amino acids destroyed per ribonuclease molecule increases with dose. In enzymatically inactive products this value is always higher by one amino acid residue than in the active components. From this result and from the increase with dose it is concluded that after destruction of one amino acid residue the ribonuclease molecule has a probability (not depending on dose of irradiation) of 0.45 to become inactivated whereas in 55 per cent of all cases the molecule maintains its enzymatic activity.

scholarly journals Low-Temperature Mineralisation of Titania-Siloxane Composite Layers

Catalysts ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 50
Author(s):  
Tomáš Svoboda ◽  
Michal Veselý ◽  
Radim Bartoš ◽  
Tomáš Homola ◽  
Petr Dzik
Keyword(s):  
Low Temperature ◽  
Great Influence ◽  
Gel Permeation Chromatography ◽  
Photocatalytic Decomposition ◽  
Acid Orange 7 ◽  
Composite Layers ◽  
Nonthermal Treatment ◽  
Plasma Methods ◽  
Voltammetric Measurements ◽  
Thermally Treated

This paper deals with low-temperature mineralisation of coatings made with titania-siloxane compositions (TSC). Methyltriethoxysilane has been adopted as the precursor for the siloxane, and during its synthesis, an oligomeric siloxane condensate with methyl moieties acting as TiO2 binder has been produced. These methyl moieties, contained in TSC, provide solubility and prevent gelling, but reduce the hydrophilicity of the system, reduce the transfer of electrons and holes generated in the TiO2. In order to avoid these unfavourable effects, TSC mineralisation can be achieved by nonthermal treatment, for example, by using UV-radiation or plasma treatment. Characterisation of the siloxane was performed by gel permeation chromatography (GPC), which showed the size of the siloxane chain. Thermogravimetric analysis revealed a temperature at which the siloxane mineralises to SiO2. Printed layers of two types of TSC with different siloxane contents were studied by a scanning electron microscope (SEM), where a difference in the porosity of the samples was observed. TSC on fluorine-doped tin oxide (FTO) coated glass and microscopic glass were treated with non-thermal UV and plasma methods. TSC on FTO glass were tested by voltammetric measurements, which showed that the non-thermally treated layers have better properties and the amount of siloxane in the TSC has a great influence on their efficiency. Samples on microscopic glass were subjected to a photocatalytic decomposition test of the model pollutant Acid orange 7 (AO7). Non-thermally treated samples show higher photocatalytic activity than the raw sample.

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