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Potassium ferrate [Fe(VI)] does not mediate self-sterilization of a surrogate Mars soil.

Crawford RL, Paszczynski A, Allenbach L - BMC Microbiol. (2003)

Bottom Line: Under ambient conditions (25 degrees C, oxygen and water present) K2FeO4 mixed into sand mineralized some reactive organic molecules to CO2, while less reactive compounds were not degraded.Similar results were observed with permanganate.Spores in oxidant-enriched sand exposed to high fluxes of UV light were protected from the sporocidal activity of the radiation below about 5 mm depths.

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Affiliation: Environmental Research Institute, University of Idaho, Moscow, ID 83844-1052, USA. crawford@uidaho.edu

ABSTRACT

Background: Martian soil is thought to be enriched with strong oxidants such as peroxides and/or iron in high oxidation states that might destroy biological materials. There is also a high flux of ultraviolet radiation at the surface of Mars. Thus, Mars may be inhospitable to life as we know it on Earth. We examined the hypothesis that if the soil of Mars contains ferrates [Fe(VI)], the strongest of the proposed oxidizing species, and also is exposed to high fluxes of UV radiation, it will be self-sterilizing.

Results: Under ambient conditions (25 degrees C, oxygen and water present) K2FeO4 mixed into sand mineralized some reactive organic molecules to CO2, while less reactive compounds were not degraded. Dried endospores of Bacillus subtilis incubated in a Mars surrogate soil comprised of dry silica sand containing 20% by weight K2FeO4 and under conditions similar to those now on Mars (extreme desiccation, cold, and a CO2-dominated atmosphere) were resistant to killing by the ferrate-enriched sand. Similar results were observed with permanganate. Spores in oxidant-enriched sand exposed to high fluxes of UV light were protected from the sporocidal activity of the radiation below about 5 mm depths.

Conclusion: Based on our data and previously published descriptions of ancient but dormant life forms on Earth, we suggest that if entities resembling bacterial endospores were produced at some point by life forms on Mars, they might still be present and viable, given appropriate germination conditions. Endospores delivered to Mars on spacecraft would possibly survive and potentially compromise life detection experiments.

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Characteristic colors of 10 mM water solutions of K2FeO4, KMnO4 and Fe2 (SO4)3. 1 = Permanganate; 2 = Potassium ferrate; 3 = Ferric chloride.
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Figure 4: Characteristic colors of 10 mM water solutions of K2FeO4, KMnO4 and Fe2 (SO4)3. 1 = Permanganate; 2 = Potassium ferrate; 3 = Ferric chloride.

Mentions: Results of spore survival over time in the control and ferrate(VI)-enriched or permanganate-enriched Mars surrogate soils under simulated Martian environmental conditions are shown in Figure 3. The endospores survived exposure to high levels of ferrate under the imposed conditions for the duration of the experiment (up to six weeks). At the times of sampling, the surrogate soil suspensions contained the characteristic crimson color of ferrate(VI) (Figure 4) or similar color of permanganate. After spreading on the agar medium, the ferrate present in the inoculum was reduced over 30 minutes to give a characteristic brown oxyhydroxy polymer precipitate of Fe(III) residue on the plate surface, indicating that ferrate(VI) was stable under the simulated Mars conditions and had been available as a potential biocide for the duration of the experiment. Spore survival was similarly high in a surrogate soil containing permanganate in place of ferrate. An important observation relevant to the Mars environment was that transient exposure of spores to K2FeO4 in the presence of liquid water was not sporocidal. Once Fe(VI) is reduced to Fe(III), a rapid process, it becomes non-toxic to the spores.


Potassium ferrate [Fe(VI)] does not mediate self-sterilization of a surrogate Mars soil.

Crawford RL, Paszczynski A, Allenbach L - BMC Microbiol. (2003)

Characteristic colors of 10 mM water solutions of K2FeO4, KMnO4 and Fe2 (SO4)3. 1 = Permanganate; 2 = Potassium ferrate; 3 = Ferric chloride.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC153549&req=5

Figure 4: Characteristic colors of 10 mM water solutions of K2FeO4, KMnO4 and Fe2 (SO4)3. 1 = Permanganate; 2 = Potassium ferrate; 3 = Ferric chloride.
Mentions: Results of spore survival over time in the control and ferrate(VI)-enriched or permanganate-enriched Mars surrogate soils under simulated Martian environmental conditions are shown in Figure 3. The endospores survived exposure to high levels of ferrate under the imposed conditions for the duration of the experiment (up to six weeks). At the times of sampling, the surrogate soil suspensions contained the characteristic crimson color of ferrate(VI) (Figure 4) or similar color of permanganate. After spreading on the agar medium, the ferrate present in the inoculum was reduced over 30 minutes to give a characteristic brown oxyhydroxy polymer precipitate of Fe(III) residue on the plate surface, indicating that ferrate(VI) was stable under the simulated Mars conditions and had been available as a potential biocide for the duration of the experiment. Spore survival was similarly high in a surrogate soil containing permanganate in place of ferrate. An important observation relevant to the Mars environment was that transient exposure of spores to K2FeO4 in the presence of liquid water was not sporocidal. Once Fe(VI) is reduced to Fe(III), a rapid process, it becomes non-toxic to the spores.

Bottom Line: Under ambient conditions (25 degrees C, oxygen and water present) K2FeO4 mixed into sand mineralized some reactive organic molecules to CO2, while less reactive compounds were not degraded.Similar results were observed with permanganate.Spores in oxidant-enriched sand exposed to high fluxes of UV light were protected from the sporocidal activity of the radiation below about 5 mm depths.

View Article: PubMed Central - HTML - PubMed

Affiliation: Environmental Research Institute, University of Idaho, Moscow, ID 83844-1052, USA. crawford@uidaho.edu

ABSTRACT

Background: Martian soil is thought to be enriched with strong oxidants such as peroxides and/or iron in high oxidation states that might destroy biological materials. There is also a high flux of ultraviolet radiation at the surface of Mars. Thus, Mars may be inhospitable to life as we know it on Earth. We examined the hypothesis that if the soil of Mars contains ferrates [Fe(VI)], the strongest of the proposed oxidizing species, and also is exposed to high fluxes of UV radiation, it will be self-sterilizing.

Results: Under ambient conditions (25 degrees C, oxygen and water present) K2FeO4 mixed into sand mineralized some reactive organic molecules to CO2, while less reactive compounds were not degraded. Dried endospores of Bacillus subtilis incubated in a Mars surrogate soil comprised of dry silica sand containing 20% by weight K2FeO4 and under conditions similar to those now on Mars (extreme desiccation, cold, and a CO2-dominated atmosphere) were resistant to killing by the ferrate-enriched sand. Similar results were observed with permanganate. Spores in oxidant-enriched sand exposed to high fluxes of UV light were protected from the sporocidal activity of the radiation below about 5 mm depths.

Conclusion: Based on our data and previously published descriptions of ancient but dormant life forms on Earth, we suggest that if entities resembling bacterial endospores were produced at some point by life forms on Mars, they might still be present and viable, given appropriate germination conditions. Endospores delivered to Mars on spacecraft would possibly survive and potentially compromise life detection experiments.

Show MeSH
Related in: MedlinePlus