Spacecraft microbes: Difference between revisions
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==Spacecraft Environments== | ==Spacecraft Environments== | ||
As stated the type of environment available to microbes is fundamentally determined by the presence or absence of humans on the mission. Increased radiation exposure and microgravity are common | As stated the type of environment available to microbes is fundamentally determined by the presence or absence of humans on the mission. Increased radiation exposure and microgravity are common challenges faced by microbes in each environment. Early experiments seemed to show no effect of microgravity on cells smaller than 10 µm in diameter (Pollard et al 1967), but later experiments demonstrated an indirect lag on the metabolism of nonmotile bacteria due to reduced material exchange with surrounding fluid made more static without gravity (Klaus et al. 2004 and Thevenet 1996). Conversely damage by ionizing radiation is a serious hazard to microbial DNA causing double-stranded breaks, mutations, or irreversible destruction. Bacteria have evolved techniques to deal with genetic damage that include homologous and nonhomologous end-joining and protein-protection in spores (Horneck 2010). Different strains display varying levels of resistance and threshold lethality to radiation-induced damage (Horneck 2010). | ||
===Manned Spacecraft and Space Stations=== | ===Manned Spacecraft and Space Stations=== | ||
The interior of hermetically sealed spacecraft designed for human occupancy provide many opportunities for microbial populations. The same conditions that create an oasis of Earth-like conditions for humans benefit their commensal microbial partners as well. Conditions inside the craft are aerobic, warm, and generally ideal for mesophilic heterotrophs (bioshmars). | |||
The first and probably richest microenvironment inside the craft is the astronauts themselves. The natural human microbiota accompanies them on their journey (bioshmars). Human bodies provide a rich source of carbon sources and nutrients and the commensal and mutuaistic members of our skin and body cavity microbial ecosystems probably are the most substantial source of inoculation to a craft's interior. However, this of course means that pathogens, particularly opportunistic pathogens, can just as easily enter which has been demonstrated in previous research (bioshmars). | The first and probably richest microenvironment inside the craft is the astronauts themselves. The natural human microbiota accompanies them on their journey (bioshmars). Human bodies provide a rich source of carbon sources and nutrients and the commensal and mutuaistic members of our skin and body cavity microbial ecosystems probably are the most substantial source of inoculation to a craft's interior. However, this of course means that pathogens, particularly opportunistic pathogens, can just as easily enter which has been demonstrated in previous research (bioshmars). | ||
Surfaces of the craft also provide adequate environments for many bacteria. Microbes that colonize the infrastructure and equipment are termed technofiles and can be a serious threat to the craft's integrity (bioshmars). Bacterial-fungal associations will form on polymers to utilize them as a carbon source and release enzymes and acids that further corrode the polymers (bioshmars). Biodegredation of polymers in this way can also release volatile noxious byproducts that can adversely affect air quality (Novikova 2002). Microbes can also exploit organic deposits on metal surfaces and similarly the metal through release of enzymes and organic acids(bioshmars). Polymer and surface corrosion were both observed on the MIR space station (Novikova 2004) and technophile bacterial strains have been detected on the | Surfaces of the craft also provide adequate environments for many bacteria. Microbes that colonize the infrastructure and equipment are termed technofiles and can be a serious threat to the craft's integrity (bioshmars). Bacterial-fungal associations will form on polymers to utilize them as a carbon source and release enzymes and acids that further corrode the polymers (bioshmars). Biodegredation of polymers in this way can also release volatile noxious byproducts that can adversely affect air quality (Novikova 2002). Microbes can also exploit organic deposits on metal surfaces and similarly the metal through release of enzymes and organic acids(bioshmars). Polymer and surface corrosion were both observed on the MIR space station (Novikova 2004) and technophile bacterial strains have been detected on the International Space Station(Novikova 2006). | ||
Another target environment for microbes aboard spacecraft are life-support systems. This too can lead to dangers if colonization impairs equipment. Water filtration and regeneration systems and coolant lines must be monitored to guard against biofilm formation that can clog up tubing and prevent necessary flow (bioshmars). However it is in life support systems where microbes perhaps show the most promise for occupying a constructive niche in the spaceraft ecosystem. Because microbes play a role in nearly every a major biogeochemical process on Earth they will undoubtedly be a part in establishing artificial biospheres in future spaceflight (Roberts et. al 2004). | Another target environment for microbes aboard spacecraft are life-support systems. This too can lead to dangers if colonization impairs equipment. Water filtration and regeneration systems and coolant lines must be monitored to guard against biofilm formation that can clog up tubing and prevent necessary flow (bioshmars). However it is in life support systems where microbes perhaps show the most promise for occupying a constructive niche in the spaceraft ecosystem. Because microbes play a role in nearly every a major biogeochemical process on Earth they will undoubtedly be a part in establishing artificial biospheres in future spaceflight (Roberts et. al 2004). | ||
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===Unmanned and Robotic Spacecraft=== | ===Unmanned and Robotic Spacecraft=== | ||
Unmanned craft and the exteriors of manned spacecraft represent a far more extreme environment for microbes. This is due to the both the physical extremes of space itself and the rigorous sterilization procedures applied prior to launch (Space Microbiology, Nicholson 2009, Moissl-Echinger 2012). There are no friendly Earth-simulated environments on these craft and thus bacteria capable of colonizing are usually endospore-forming or extremophiles. | |||
Outer space is a very harsh environment for life in virtually all respects. Microbes face desiccation, strong radiation, extremes of temperature, and scarce nutrients (space microbiology). Experimentation has been conducted since the earliest days of space flight to determine microbial survival capabilities in space. The 1972 Apollo 16 mission used the MEED facility installed on the outside of the command module possessing 798 sample cuvettes with varying levels of exposure to the vacuum of space or solar UV radiation (space microbiology). The most recent experimentation were conducted by the EXPOSE facilities on the International Space Station in 2008 and 2009 (space microbiology, NPR). Very few organisms have demonstrated the ability to survive the onslaught of full exposure to space (Space Microbiology). Among them are lichens Rhizocarpon geographicum and Xanthoria elegans and the cyanobacteria Synechococcus, and it should be noted that these organisms were dormant during their exposure and Synechococcus was protected in a gypsum-halite crystal (Space Microbioloy). Shielding from ultraviolet light seems to allow for higher incidence of microbe survival for several years (Space Microbiiology, NPR). Even if the craft is destined for a celestial body with an atmosphere and a microbe survives the journey the alien atmosphere and surface temperatures are likely not favorable for growth (Space Microbiology). | |||
The effects of radiation are mentioned above, but a unique problem for microbes exposed to the vacuum of space is extreme desiccation (Space Microbiology). It induces conformational changes in DNA that make it more susceptible to radiation damage (Falk 194). Lipid membranes may change conformation from planar to cylindrical and amino acids, carbohydrates, and nucleic acids may all polymerize together (Cox 1993). Even UV-shielded but vacuum-exposed spore-forming microbes (bacteria and fungi) did not cope much better with the desiccation and required protecting sugars or salts for their spores to survive (Space Microbiology). | |||
The exterior of spacecraft also represent an extreme environment because of the extensive decontamination procedures employed before launch. This is done to avoid the transport of terrestrial microbes to other celestial bodies, known as forward contamination, and also the hypothetical return of potentially dangerous extraterrestrial life to Earth, known as back contamination (Nicholson 2009). Protection of forward and back contamination is mandated under the 1967 U.N. Outer Space Treaty for all space travel (Nicholson 2009, Probst 2010). A related motivation is the desire to avoid confounding variables in life-detection research (Moissi-Eichinger 2012, Nicholson 2009, Probst 2010). This concern came to the forefront when it was the suspected that late alterations to the Mars Curiosity rover’s drill may have introduced microbial and physical contamination (NPR, Space.com). The space craft are constructed and sterilized in clean rooms that are kept low in nutrient content, humidity, and air particulates and are frequently and comprehensively cleaned with disinfectants (Nicholson 2009). Quality control checks have traditionally involved culturing but are increasingly employing molecular techniques (Probst 2010, Moissl-Eichinger 2012, Nicholson 2009). While these procedures may eliminate most microbes they unfortunately also select for the extremophiles, which are the most likely group to survive a space-flight (Nicholson 2009). | |||
==Microbial Communities== | |||
As follows from the differences in environment, microbial communities differ dramatically between manned and unmanned spacecraft. The advent of molecular methods has allowed for further refinement of the microbe community composition in these locales. | |||
Manned space flights have demonstrated | |||
Revision as of 21:10, 7 April 2013
Spacecraft Microbiology
Spacecraft represent a unique environment for microbes. Spacecraft are generally classified as either manned or unmanned and this distinction carries profound consequences on the microbial ecology of the crafts. As on Earth, microbial communities can have both positive and negative effects. While they present hazards like degradation of equipment, infection, and contamination they also offer the promise for advanced life support systems.
Spacecraft Environments
As stated the type of environment available to microbes is fundamentally determined by the presence or absence of humans on the mission. Increased radiation exposure and microgravity are common challenges faced by microbes in each environment. Early experiments seemed to show no effect of microgravity on cells smaller than 10 µm in diameter (Pollard et al 1967), but later experiments demonstrated an indirect lag on the metabolism of nonmotile bacteria due to reduced material exchange with surrounding fluid made more static without gravity (Klaus et al. 2004 and Thevenet 1996). Conversely damage by ionizing radiation is a serious hazard to microbial DNA causing double-stranded breaks, mutations, or irreversible destruction. Bacteria have evolved techniques to deal with genetic damage that include homologous and nonhomologous end-joining and protein-protection in spores (Horneck 2010). Different strains display varying levels of resistance and threshold lethality to radiation-induced damage (Horneck 2010).
Manned Spacecraft and Space Stations
The interior of hermetically sealed spacecraft designed for human occupancy provide many opportunities for microbial populations. The same conditions that create an oasis of Earth-like conditions for humans benefit their commensal microbial partners as well. Conditions inside the craft are aerobic, warm, and generally ideal for mesophilic heterotrophs (bioshmars).
The first and probably richest microenvironment inside the craft is the astronauts themselves. The natural human microbiota accompanies them on their journey (bioshmars). Human bodies provide a rich source of carbon sources and nutrients and the commensal and mutuaistic members of our skin and body cavity microbial ecosystems probably are the most substantial source of inoculation to a craft's interior. However, this of course means that pathogens, particularly opportunistic pathogens, can just as easily enter which has been demonstrated in previous research (bioshmars).
Surfaces of the craft also provide adequate environments for many bacteria. Microbes that colonize the infrastructure and equipment are termed technofiles and can be a serious threat to the craft's integrity (bioshmars). Bacterial-fungal associations will form on polymers to utilize them as a carbon source and release enzymes and acids that further corrode the polymers (bioshmars). Biodegredation of polymers in this way can also release volatile noxious byproducts that can adversely affect air quality (Novikova 2002). Microbes can also exploit organic deposits on metal surfaces and similarly the metal through release of enzymes and organic acids(bioshmars). Polymer and surface corrosion were both observed on the MIR space station (Novikova 2004) and technophile bacterial strains have been detected on the International Space Station(Novikova 2006).
Another target environment for microbes aboard spacecraft are life-support systems. This too can lead to dangers if colonization impairs equipment. Water filtration and regeneration systems and coolant lines must be monitored to guard against biofilm formation that can clog up tubing and prevent necessary flow (bioshmars). However it is in life support systems where microbes perhaps show the most promise for occupying a constructive niche in the spaceraft ecosystem. Because microbes play a role in nearly every a major biogeochemical process on Earth they will undoubtedly be a part in establishing artificial biospheres in future spaceflight (Roberts et. al 2004).
Unmanned and Robotic Spacecraft
Unmanned craft and the exteriors of manned spacecraft represent a far more extreme environment for microbes. This is due to the both the physical extremes of space itself and the rigorous sterilization procedures applied prior to launch (Space Microbiology, Nicholson 2009, Moissl-Echinger 2012). There are no friendly Earth-simulated environments on these craft and thus bacteria capable of colonizing are usually endospore-forming or extremophiles.
Outer space is a very harsh environment for life in virtually all respects. Microbes face desiccation, strong radiation, extremes of temperature, and scarce nutrients (space microbiology). Experimentation has been conducted since the earliest days of space flight to determine microbial survival capabilities in space. The 1972 Apollo 16 mission used the MEED facility installed on the outside of the command module possessing 798 sample cuvettes with varying levels of exposure to the vacuum of space or solar UV radiation (space microbiology). The most recent experimentation were conducted by the EXPOSE facilities on the International Space Station in 2008 and 2009 (space microbiology, NPR). Very few organisms have demonstrated the ability to survive the onslaught of full exposure to space (Space Microbiology). Among them are lichens Rhizocarpon geographicum and Xanthoria elegans and the cyanobacteria Synechococcus, and it should be noted that these organisms were dormant during their exposure and Synechococcus was protected in a gypsum-halite crystal (Space Microbioloy). Shielding from ultraviolet light seems to allow for higher incidence of microbe survival for several years (Space Microbiiology, NPR). Even if the craft is destined for a celestial body with an atmosphere and a microbe survives the journey the alien atmosphere and surface temperatures are likely not favorable for growth (Space Microbiology).
The effects of radiation are mentioned above, but a unique problem for microbes exposed to the vacuum of space is extreme desiccation (Space Microbiology). It induces conformational changes in DNA that make it more susceptible to radiation damage (Falk 194). Lipid membranes may change conformation from planar to cylindrical and amino acids, carbohydrates, and nucleic acids may all polymerize together (Cox 1993). Even UV-shielded but vacuum-exposed spore-forming microbes (bacteria and fungi) did not cope much better with the desiccation and required protecting sugars or salts for their spores to survive (Space Microbiology).
The exterior of spacecraft also represent an extreme environment because of the extensive decontamination procedures employed before launch. This is done to avoid the transport of terrestrial microbes to other celestial bodies, known as forward contamination, and also the hypothetical return of potentially dangerous extraterrestrial life to Earth, known as back contamination (Nicholson 2009). Protection of forward and back contamination is mandated under the 1967 U.N. Outer Space Treaty for all space travel (Nicholson 2009, Probst 2010). A related motivation is the desire to avoid confounding variables in life-detection research (Moissi-Eichinger 2012, Nicholson 2009, Probst 2010). This concern came to the forefront when it was the suspected that late alterations to the Mars Curiosity rover’s drill may have introduced microbial and physical contamination (NPR, Space.com). The space craft are constructed and sterilized in clean rooms that are kept low in nutrient content, humidity, and air particulates and are frequently and comprehensively cleaned with disinfectants (Nicholson 2009). Quality control checks have traditionally involved culturing but are increasingly employing molecular techniques (Probst 2010, Moissl-Eichinger 2012, Nicholson 2009). While these procedures may eliminate most microbes they unfortunately also select for the extremophiles, which are the most likely group to survive a space-flight (Nicholson 2009).
Microbial Communities
As follows from the differences in environment, microbial communities differ dramatically between manned and unmanned spacecraft. The advent of molecular methods has allowed for further refinement of the microbe community composition in these locales. Manned space flights have demonstrated
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