Assessment of Planetary Protection Requirements for Spacecraft Missions to Icy Solar System Bodies (2012) / Chapter Skim
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5 Microbial Metabolism and Physiology
5 Microbial Metabolism and Physiology
Pages 41-54
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From page 41... ...
The cold environments of icy bodies might provide habitats for terrestrial microbes that can grow only at very low temperatures. On Earth, environments capable of supporting microbial growth at 0°C or below typically include temperate and high-latitude marine environments, high-latitude ice, soils, cryopegs, the upper atmosphere, seasonally cold soils, and dairy products, meats, and seafoods that are maintained at low temperature.
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From page 42... ...
However, complex ecosystems exist in oligiotrophic environments where the concentration of phosphate is lower than the lowest concentration that either prevents growth or induces stress responses in most isolated microbes tested. Oligiotrophic oceans such as the Sargasso Sea in the northwestern Atlantic, the North Pacific subtropical gyre, and eastern part of the Mediterranean Sea have extremely low levels of dissolved phosphate.
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From page 43... ...
The dominant heterotrophic bacteria in these oligiotrophic oceans, Pelagobacter ubique, can like the Prochlorococcus species grow in situ in phosphate at low concentrations while utilizing carbon com pounds in the low levels found in the dissolved organic compound fraction. 22 Both of these organisms are small (<1 µm)
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From page 44... ...
44 PLANETARY PROTECTION REQUIREMENTS FOR SPACECRAFT MISSIONS TO ICY SOLAR SYSTEM BODIES TABLE 5.1 Examples of Electron Donors or Acceptors for Life in Icy Bodies Both Inferred and Measured in Past Work Europa Comments Enceladus Comments Titan Comments Electron Donors (observed) Organics Detected Expected on the Organic Methane and Organics and methane Surface on surface surface.
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From page 45... ...
Unlike many terrestrial extremophiles that grow within a singular extreme environment, species of the genus Deinococcus demonstrate a suite of extreme survival advantages similar to that needed to survive multiple chal lenges encountered on missions to the outer planets. One of these species, Deinococcus radiodurans, can survive exposures to ionizing radiation (x rays and gamma rays)
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From page 46... ...
Daly, and P R02216 Setlow, Effects of Mn and Fe levels on Bacillus subtilis spore resistance and effects of Mn2+, other divalent cations, ortho phosphate, and dipicolinic acid on protein resistance to ionizing radiation, Applied and Environmental Microbiology 77:32-40, vector editable 2011; M.J.
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From page 47... ...
Psychrophiles can grow only over a limited temperature range that does not exceed 20°C to 30°C, whereas the temperature range of growth for psychrotolerant microorganisms is somewhat broader at 30°C to 40°C. Thus, for both kinds of physiology, the anticipated maximum growth temperature lies between −5°C and 40°C.
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From page 48... ...
The overall conclusion is that psychrophiles and psychrotolerant microorganisms are not adapted at the molecular level to grow or survive at temperatures much more than10°C above their maximum growth temperature. Therefore, to meet planetary protection requirements for missions to the icy bodies, heating of the spacecraft or its sealed components to 60°C for 5 hours will provide sufficient bioload reduction for non-spore-forming psychrophiles and psychrotolerant microorganisms.
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From page 49... ...
SOURCE: A.D.Warth, Relationship between the heat resistance of spores and the optimum and maximum growth temperatures of Bacillus species, Journal of Bacteriology 134:699-705, 1978. few examples of cold-tolerant, spore-forming organisms that are known require complex organic compounds to grow.
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From page 50... ...
Raes, and J.-Y. Matroule, Phosphate starva tion triggers production and secretion of an extracellular lipoprotein in Caulobacter crescentus, Public Library of Science One 5:1-11, 2010.
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From page 51... ...
Daly, How radiation kills cells: Survival of Deinococcus radiodurans and Shewanella oneidensis under oxidative stress, FEMS Microbiology Reviews 29:361-375, 2005.
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From page 52... ...
DiRuggiero, Salt shield: intra cellular salts provide cellular protection against ionizing radiation in the halophilic archaeon, Halobacterium salinarum NRC-1, Environmental Microbiology 11:1066-1078, 2009.
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From page 53... ...
Daly, and P Setlow, Effects of Mn and Fe levels on Bacillus subtilis spore resistance and effects of Mn2+, other divalent cations, orthophosphate, and dipicolinic acid on protein resistance to ionizing radiation, Applied and Environmental Microbiology 77:32-40, 2011.
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From page 54... ...
A.D. Warth, Relationship between the heat resistance of spores and the optimum and maximum growth temperatures of Bacillus species, Journal of Bacteriology 134:699-705, 1978.
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