Forward Contamination Research Articles

Planetary protection for human exploration of Mars

Human astronauts have unique capabilities that could greatly facilitate scientific exploration of other planets. However, when searching for life beyond Earth, these capabilities can be utilized effectively only if the biological contamination associated with human presence is monitored and minimized. This is termed planetary protection, and is a critical element in human exploration beyond Earth. Planetary protection must be incorporated from the earliest stages of mission planning and development, to ensure proper implementation. Issues involve both “forward contamination”, the contamination of other solar system bodies by Earth microbes and organic materials, and “backward contamination”, the contamination of Earth systems, including astronauts, by biological hazards or potential alien life. Conclusions from a number of international workshops held over the last six years recognize that some degree of forward contamination associated with human astronaut explorers is inevitable. Nevertheless, when humans are exploring space the principles and policies of planetary protection, developed by COSPAR in accordance with the 1967 Outer Space Treaty, still apply. Implementation guidelines include documenting and minimizing contamination of the exploration targets, control at the most stringent levels for locations in which Earth life might grow, and protection of humans from exposure to untested planetary materials. Preventing harmful contamination of the Earth must be of the highest priority for all missions.

Rapid Culture-Independent Microbial Analysis Aboard the International Space Station (ISS)

A new culture-independent system for microbial monitoring, called the Lab-On-a-Chip Application Development Portable Test System (LOCAD-PTS), was operated aboard the International Space Station (ISS). LOCAD-PTS was launched to the ISS aboard Space Shuttle STS-116 on December 9, 2006, and has since been used by ISS crews to monitor endotoxin on cabin surfaces. Quantitative analysis was performed within 15 minutes, and sample return to Earth was not required. Endotoxin (a marker of Gram-negative bacteria) was distributed throughout the ISS, despite previous indications that mostbacteria on ISS surfaces were Gram-positive [corrected].Endotoxin was detected at 24 out of 42 surface areas tested and at every surface site where colony-forming units (cfu) were observed, even at levels of 4-120 bacterial cfu per 100 cm(2), which is below NASA in-flight requirements (<10,000 bacterial cfu per 100 cm(2)). Absent to low levels of endotoxin (<0.24 to 1.0 EU per 100 cm(2); defined in endotoxin units, or EU) were found on 31 surface areas, including on most panels in Node 1 and the US Lab. High to moderate levels (1.01 to 14.7 EU per 100 cm(2)) were found on 11 surface areas, including at exercise, hygiene, sleeping, and dining facilities. Endotoxin was absent from airlock surfaces, except the Extravehicular Hatch Handle (>3.78 EU per 100 cm(2)). Based upon data collected from the ISS so far, new culture-independent requirements (defined in EU) are suggested, which are verifiable in flight with LOCAD-PTS yet high enough to avoid false alarms. The suggested requirements are intended to supplement current ISS requirements (defined in cfu) and would serve a dual purpose of safeguarding crew health (internal spacecraft surfaces <20 EU per 100 cm(2)) and monitoring forward contamination during Constellation missions (surfaces periodically exposed to the external environment, including the airlock and space suits, <0.24 EU per 100 cm(2)).

Improved MEUF removal of naphthenic acids from produced water

Naphthenic acids are naturally occurring organics in produced waters from oil recovery operations. In principle, these contaminants can be removed using micellar-enhanced ultrafiltration (MEUF), which is an effective technique for the removal of organic contaminants from water streams. In this work, we show that the amphiphilic nature of the naphthenic acids contributed to decreasing the critical micelle concentration (CMC) of cetylpyridinium chloride (CPC), a widely used surfactant in MEUF. This reduction in CMC allowed a decrease in the CPC dosage required to attain certain removal of the organics, and hence, improved the performance of traditional MEUF as a result of reducing back contamination and potential fouling of the membrane. The effect of CPC feed concentration, and the concentration and carbon number of the naphthenic acids on permeate flux, recovery ratio and percent rejection of CPC and naphthenic acids were explored over a range of trans-membrane pressure. The MEUF setup employed hydrophilic polyacrylonitrile (PAN) hollow fiber membrane with 13 kDa MWCO, since it allowed for high permeate flux and contaminant rejection.

Design and Practices for Use of Automated Drilling and Sample Handling in MARTE While Minimizing Terrestrial and Cross Contamination

Mars Astrobiology Research and Technology Experiment (MARTE) investigators used an automated drill and sample processing hardware to detect and categorize life-forms found in subsurface rock at Río Tinto, Spain. For the science to be successful, it was necessary for the biomass from other sources--whether from previously processed samples (cross contamination) or the terrestrial environment (forward contamination)-to be insignificant. The hardware and practices used in MARTE were designed around this problem. Here, we describe some of the design issues that were faced and classify them into problems that are unique to terrestrial tests versus problems that would also exist for a system that was flown to Mars. Assessment of the biomass at various stages in the sample handling process revealed mixed results; the instrument design seemed to minimize cross contamination, but contamination from the surrounding environment sometimes made its way onto the surface of samples. Techniques used during the MARTE Río Tinto project, such as facing the sample, appear to remove this environmental contamination without introducing significant cross contamination from previous samples.

Impact of assembly, testing and launch operations on the airborne bacterial diversity within a spacecraft assembly facility clean-room

AbstractIn an effort to minimize the probability of forward contamination of pristine extraterrestrial environments, the National Aeronautics and Space Administration requires that all US robotic spacecraft undergo assembly, testing and launch operations (ATLO) in controlled clean-room environments. This study examines the impact of ATLO activity on the microbial diversity and overall bioburden contained within the air of the clean-room facility in which the Mars Exploration Rovers (MERs) underwent final preparations for launch. Air samples were collected from several facility locations and traditional culture-based and molecular methodologies were used to measure microbial burden and diversity. Surprisingly, the greatest estimates of airborne bioburden, as derived from ATP content and cultivation assays, were observed prior to the commencement of MER ATLO activities. Furthermore, airborne microbial diversity gradually declined from the initiation of ATLO on through to launch. Proteobacterial sequences were common in 16S rDNA clone libraries. Conspicuously absent were members of the Firmicutes phylum, which includes the genusBacillus. In previous studies, species of this genus were repeatedly isolated from the surfaces of spacecraft and clean-room assembly facilities. Increased cleaning and maintenance initiated immediately prior to the start of ATLO activity could explain the observed declines in both airborne bioburden and microbial diversity.

Removal of Heavy Metals from Aqueous Solutions by Precipitation-Filtration Using Novel Organo-Phosphorus Ligands

An organophosphorus mixture of sodium mono- and di-(n-hexa-decyl) phosphinate was synthesized and purified, and then used as a ligand to remove heavy metals by precipitation from aqueous nitrate, chloride, and sulfate solutions. The new ligand offers more advantages over the previously studied sodium dioctyl and dodecyl phosphinates. The sodium form of the mono- and di-(n-hexa-decyl) phosphinate has a much lower solubility in water, which contributed to much lower back contamination and much lower loss of the reagent, even when excess amount of ligand was employed. Moreover, an excess amount of the ligand did not alter the filtration characteristics of the resultant precipitate. The heavy metals: lead, cadmium, mercury, cobalt, and nickel were precipitated with the sodium mono- and di-(n-hexa-decyl) phosphinate, NaL, in the form of Pb L 2(s), Cd L 2(s), Hg L 2(s), Co L 2(s), and Ni L 2(s). In the absence of free acid in the feed, a maximum removal of each metal corresponded to the stoichiometric ratio. The residual concentrations of each of the metals at the optimum conditions were measured for the different media and found to be lower than 10 ppb, lower than the acceptable levels for most regions. Lead, as a model heavy metal, was studied in more detail. Adding an acid to the feed solution reduced the removal of lead as some of the phosphinate ligand was converted to the acid form. The presence of chloride and sulfate in the feed solution; up to mole ratios to lead of 5000, and of calcium in the feed solution; up to mole ratio to lead of 200, had no effect on the removal of lead. The ligand was more selective to lead than the other four metals, and the selectivity was in the order Pb > Cd > Co & Ni > Hg. The ligand was regenerated up to 99.99% and the metals were recovered in 100 times more concentrated aqueous solutions.

AustroMars and PolAres: Measuring forward contamination during Mars-analogue missions

The search for life on Mars is one of the most ambitious scientific challenges in astrobiology. Although the surface of the planet is generally believed to be hostile to life, habitats embedded in the subsurface water repositories might harbor diminutive traces of extant or even extant life requiring advanced analytical capabilities. At the same time, hardware (including a human crew) delivered from Earth introduces the inherent risk of contaminating the very samples to be investigated for tracers of life and as such might compromise the pristinity of the sample leading to a false-positive detection. Deep subsurface drilling activities are considered to be one of the most promising sampling techniques, but require extensive infrastructure and technologies yet to be developed and increase the probability of such a forward contamination. AustroMars and PolAres are two Mars-analogue research programmes conducted by the Austrian Space Forum to investigate the contamination vectors of human Mars surface activities. Using fluorescent microspherules and non-pathogenic bacteria, an analysis strategy to quantify the bioload transfer rates and its field application in a Mars-analogue setting is described.

Planetary protection for humans in space: Mars and the Moon

When searching for life beyond Earth, the unique capabilities provided by human astronauts will only be advantageous if the biological contamination associated with human presence is monitored and minimized. Controlling biological contamination during planetary exploration is termed ‘planetary protection,’ and will be a critical element in the human exploration of other solar system bodies. To ensure the safety and health of the astronauts and the Earth, while preserving science value, planetary protection considerations must be incorporated from the earliest stages of mission planning and development. Issues of concern to planetary protection involve both ‘forward contamination,’ which is the contamination of other solar system bodies by Earth microbes and organic materials, and ‘backward contamination,’ which is the contamination of Earth systems by potential alien life. Forward contamination concerns include contamination that might invalidate current or future scientific exploration of a particular solar system body, and that may disrupt the planetary environment or a potential endogenous (alien) ecosystem. Backward contamination concerns include both immediate and long-term effects on the health of the astronaut explorers from possible biologically active materials encountered during exploration, as well as the possible contamination of the Earth. A number of national and international workshops held over the last seven years have generated a consensus regarding planetary protection policies and requirements for human missions to Mars, and a 2007 workshop held by NASA has considered the issues and benefits to planetary protection that might be offered by a return to the Moon. Conclusions from these workshops recognize that some degree of forward contamination associated with human astronaut explorers is inevitable. Nonetheless, the principles and policies of planetary protection, developed by COSPAR in conformance with the 1967 Outer Space Treaty, can and should be followed when humans are exploring space. Implementation guidelines include documenting and minimizing contamination of the exploration targets, protection at the most stringent levels for any target locations in which Earth life might grow, protection of humans from exposure to untested planetary materials, and preventing harmful contamination of the Earth as the highest priority for all missions. These considerations should be incorporated in planning for future human exploration missions.

An ethical approach to planetary protection

What hazards might biological contamination pose to planets, comets and other celestial bodies visited by probes launched from Earth? What hazards might returning probes pose to Earth and its inhabitants? What should be considered an acceptable level of risk? What technologies, procedures and constraints should be applied? What sort of attitude has to be chosen concerning human crews, who themselves could become both contaminated victims and contaminating agents? The vast issue of planetary protection must, more than ever, spark ethical debate. Space treaty, COSPAR recommendations offer borders and context for this reflection, which has to be introduced in the actual humanist: never has been anthropocentrism so practical and concerned, in the same time, by the next generations, because of the historical character of life. At least an ethics of risk is necessary (far from the myth of zero-risk) for all the three types of contamination: other celestial bodies (forward contamination), Earth (backward contamination) and astronauts.

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-microm-filtered desert soil (DSE) microcosms and desiccated for 75 days on aluminum died, whereas cells prepared similarly in 60-microm-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 (approximately 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.

Slow degradation of ATP in simulated martian environments suggests long residence times for the biosignature molecule on spacecraft surfaces on Mars

Prelaunch planetary protection protocols on spacecraft are designed to reduce the numbers and diversity of viable bioloads on surfaces in order to mitigate the forward contamination of planetary surfaces. In addition, there is a growing appreciation that prelaunch spacecraft cleaning protocols will be required to reduce the levels of biogenic signature molecules on spacecraft to levels that will not compromise life-detection experiments on landers. The biogenic molecule, adenosine triphosphate (ATP) was tested for long-term stability under simulated Mars surface conditions of high UV flux, low temperature, low pressure, Mars atmosphere, and clear-sky dust loading conditions. Data on UV-induced ATP degradation rates were then extrapolated to a diversity of global conditions using a radiative transfer model for UV on Mars. The UV-induced degradation of ATP tested at 4.1 W m −2 UVC (200–280 nm), −10 °C, 7.1 mb, 95% CO 2 gas composition, and an atmospheric opacity of τ = 0.1 yielded a half-life for ATP of 1342 kJ m −2; or extrapolated to approximately 22 sols on equatorial Mars with an atmospheric opacity of τ = 0.5 . Temperature was found to moderately affect ATP degradation rates under martian conditions; tests at −80 or 20 °C yielded ATP half-lives of 2594 or 1183 kJ m −2, respectively. The ATP degradation rates reported here are over 10 orders of magnitude slower than the UV-induced biocidal rates reported in the literature on the inactivation of strongly UV-resistant bacterial spores from Bacillus pumilus SAFR-032 [Schuerger, A.C., Richards, J.T., Newcombe, D.A., Venkateswaran, K.J., 2006. Icarus 181, 52–62]. Extrapolating results to global Mars conditions, residence times for a 99% reduction of ATP on spacecraft surfaces ranged from 158 sols on Sun-exposed surfaces to approximately 32,000 sols for the undersides of landers similar to Viking. However, spacecraft materials greatly affected the survival times of ATP under martian conditions. Stainless steel was found to enhance the UV degradation of ATP by over 2 orders of magnitude compared to ATP-doped iridited aluminum, graphite, and astroquartz coupons. Extrapolating these results to global conditions, ATP on stainless steel might be expected to persist between 2 and 320 sols for upper and lower surfaces of landers. Liquid chromatography-mass spectrometry data supported the conclusion that UV irradiation acted to remove the γ-phosphate group from ATP, and no evidence was observed for the UV-degradation of d-ribose or adenine moieties. Long residence times for ATP on spacecraft materials under martian conditions suggest that prelaunch cleaning protocols may need to be strengthened to mitigate against possible ATP contamination of life-detection experiments on Mars landers.

Archaeal diversity analysis of spacecraft assembly clean rooms

One of the main tasks of NASA's planetary protection program is to prevent the forward contamination of extraterrestrial environments with Earth life, and in turn preserve other planets and the integrity of future life detection missions. Despite information regarding bacterial diversity in NASA's clean rooms, little is known about the presence of Archaea. Archaeal community analysis of spacecraft-associated surfaces is important, as they are considered by some to represent terrestrial life most capable of surviving on Mars. The first insights into the archaeal diversity of clean rooms where spacecraft assembled are attempted. Nucleic acid sequences clustering with uncultivable Archaea within the Eury- and Crenarchaeota were retrieved from 8 of 26 samples collected from several spacecraft assembly clean rooms. Due to their potential capability to survive and proliferate in Martian conditions, screening for Archaea on spacecraft surfaces and instruments that are associated with future life detection missions may be necessary.

Biological assessment of Ariane 5 fairing

United Nations Space Treaties [ United Nations, Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies, 610 UNTS 205, resolution 2222(XXI) of December 1966., United Nations, Agreement Governing the Activities of States on the Moon and Other Celestial Bodies, UN doc A/RES/34/68, resolution 38/68 of December 1979.] require the preservation of planets and of Earth from contamination. All nations part to these Treaties shall take measures to prevent forward and backward contamination during missions exploring our solar system. As observer for the United Nations Committee on Peaceful Uses of Outer Space, the COSPAR (Committee of Space Research) defines and handles the applicable policy and proposes recommendations to Space Agencies [COSPAR Planetary Protection Panel, Planetary Protection Policy accepted by the COSPAR Council and Bureau, 20 October 2002, amended 24 March 2005. http://www.cosparhq.org/scistr/PPPolicy.htm.]. The goal is to protect celestial bodies from terrestrial biological contamination as well as to protect the Earth environment from an eventual biohazard which may be carried by extraterrestrial samples or by space systems returning to Earth. According to the applicable specifications, including in our case the French requirements [ CNES, System Safety. Planetary Protection Requirements. Normative referential CNES RNC-CNES-R-14, CNES Toulouse, ed. 4, 04 October 2002.], the prevention of forward contamination is accomplished by reducing the bioburden on space hardware to acceptable, prescribed levels, including in some instances system sterilization, assembling and integrating the appropriate spacecraft systems in cleanrooms of appropriate biological cleanliness, avoiding or controlling any recontamination risk, and limiting the probability impact of space systems. In order to prepare for future exploration missions [ Debus, A., Planetary protection: organization requirements and needs for future planetary exploration missions, ESA conference publication SP-543, pp 103–114, 2003.], and in particular for missions to Mars requiring to control the spacecraft bioburden, a test program has been developed to evaluate the biological contamination under the fairing of the Ariane 5 launcher.

Monitoring of Hydrocarbon Gaseous Compounds formed During Bioleaching of Copper Sulphide Minerals with Mesophilic Microorganisms

An experimental campaign was conducted for monitoring the formation of hydrocarbon gaseous compounds during bioleaching of copper sulphide ores with mesophilic microorganisms. Three different mineral samples were used: a pyrite concentrate, a chalcopyrite concentrate and a copper sulphide ore rock from El Teniente mine containing 1 % copper. Mineral samples were bioleached in 250 ml shake flasks containing 100 ml of basal medium inoculated either with a pure strain of Acidithiobacillus ferrooxidans or a natural bacteria consortium obtained from the acid leaching of El Teniente ore in columns. Each sealed system shake flask was fed with a flow of synthetic air and the exit stream was passed through a column containing an adsorbent material and next through a water trap as to avoid back air contamination from the environment. Compounds present in the adsorbent material after 90 days of bioleaching were analysed using a gas chromatography mass spectrometry technique with a procedure that detects 162 different hydrocarbon gaseous compounds (SGH). Results showed that the bacterial communities in copper sulphide bioleaching results in the formation of some hydrocarbon gaseous compounds, mainly various types of methyl benzene and branched alkanes. The formation of these organic compounds is likely to be related to the presence of heterothrofic microorganisms present in the natural populations.

Isolation and Characterization of Bacteria Capable of Tolerating the Extreme Conditions of Clean Room Environments

In assessing the bacterial populations present in spacecraft assembly, spacecraft test, and launch preparation facilities, extremophilic bacteria (requiring severe conditions for growth) and extremotolerant bacteria (tolerant to extreme conditions) were isolated. Several cultivation approaches were employed to select for and identify bacteria that not only survive the nutrient-limiting conditions of clean room environments but can also withstand even more inhospitable environmental stresses. Due to their proximity to spacefaring objects, these bacteria pose a considerable risk for forward contamination of extraterrestrial sites. Samples collected from four geographically distinct National Aeronautics and Space Administration clean rooms were challenged with UV-C irradiation, 5% hydrogen peroxide, heat shock, pH extremes (pH 3.0 and 11.0), temperature extremes (4 degrees C to 65 degrees C), and hypersalinity (25% NaCl) prior to and/or during cultivation as a means of selecting for extremotolerant bacteria. Culture-independent approaches were employed to measure viable microbial (ATP-based) and total bacterial (quantitative PCR-based) burdens. Intracellular ATP concentrations suggested a viable microbial presence ranging from below detection limits to 10(6) cells/m(2). However, only 0.1 to 55% of these viable cells were able to grow on defined culture medium. Isolated members of the Bacillaceae family were more physiologically diverse than those reported in previous studies, including thermophiles (Geobacillus), obligate anaerobes (Paenibacillus), and halotolerant, alkalophilic species (Oceanobacillus and Exiguobacterium). Non-spore-forming microbes (alpha- and beta-proteobacteria and actinobacteria) exhibiting tolerance to the selected stresses were also encountered. The multiassay cultivation approach employed herein enhances the current understanding of the physiological diversity of bacteria housed in these clean rooms and leads us to ponder the origin and means of translocation of thermophiles, anaerobes, and halotolerant alkalophiles into these environments.

Testing interplanetary transfer of bacteria between Earth and Mars as a result of natural impact phenomena and human spaceflight activities

Interplanetary transport of microbes between Earth and Mars can be envisioned to occur either naturally as a consequence of impacts (lithopanspermia) or as a result of human and robotic spaceflight. In either case, the considerations for modeling successful transfer of microbial life are similar. The probability of microbes surviving either natural or human-mediated transfer is a function of: the initial population size and composition (i.e., the bioload); survival of launch, transit through space, entry and deposition; and ability to survive and proliferate on the recipient planet. Modeling this process for testing lithopanspermia and for mitigation of forward and back contamination for planetary protection purposes calls for accurate simulation of all aspects of transfer.

The European standard on planetary protection requirements

Since the beginning of solar system exploration, numerous spacecrafts have been sent towards others worlds, and one of the main goals of such missions is the search for extraterrestrial forms of life. It is known that, under certain conditions, some terrestrial entities are able to survive during cruises in space and that they may contaminate other planets (forward contamination). At another level, possible extraterrestrial life forms are unknown and their ability to contaminate the Earth's biosphere (back contamination) in the frame of sample return missions cannot be excluded. Article IX of the Outer Space Treaty (London/Washington, January 27, 1967) requires the preservation of planets and the Earth from contamination. All nations taking part in this Treaty must prevent forward and back contamination during missions exploring our solar system. Consequently, the United Nations (UN-COPUOS) has delegated COSPAR (Committee of Space Research) to take charge of planetary protection and, at present, all space-faring nations must comply with COSPAR policy and consequently with COSPAR planetary protection recommendations. Starting from these recommendations and the “CNES Planetary Protection Standard” document, a working group has been set up in the framework of the “European Cooperation for Space Standardization” (ECSS) to establish the main specifications for preventing cross-contamination between target bodies within the solar system and the Earth–moon system.

Activity and stability of a complex bacterial soil community under simulated Martian conditions

A simulation experiment with a complex bacterial soil community in a Mars simulation chamber was performed to determine the effect of Martian conditions on community activity, stability and survival. At three different depths in the soil core short-term effects of Martian conditions with and without ultraviolet (UV) exposure corresponding to 8 Martian Sol were compared. Community metabolic activities and functional diversity, measured as glucose respiration and versatility in substrate utilization, respectively, decreased after UV exposure, whereas they remained unaffected by Martian conditions without UV exposure. In contrast, the numbers of culturable bacteria and the genetic diversity were unaffected by the simulated Martian conditions both with and without UV exposure. The genetic diversity of the soil community and of the colonies grown on agar plates were evaluated by denaturant gradient gel electrophoresis (DGGE) on DNA extracts. Desiccation of the soil prior to experimentation affected the functional diversity by decreasing the versatility in substrate utilization. The natural dominance of endospores and Gram-positive bacteria in the investigated Mars-analogue soil may explain the limited effect of the Mars incubations on the survival and community structure. Our results suggest that UV radiation and desiccation are major selecting factors on bacterial functional diversity in terrestrial bacterial communities incubated under simulated Martian conditions. Furthermore, these results suggest that forward contamination of Mars is a matter of great concern in future space missions.

Aqueous Micellar Solvent Extraction of Phenol from Wastewater

In aqueous micellar solvent extraction (AMSE), an organic solute is extracted from an aqueous solution across an ultrafiltration membrane into a solvent consisting of an aqueous micellar surfactant solution. The solute crossing the membrane is solubilized in the surfactant micelles, which are retained by the membrane. Phenol was extracted from water into an aqueous solution of sodium dodecyl sulfate (SDS) in hollow fiber membrane contactors of 5 K and 10 K molecular weight cutoff. The objectives were to determine the effect of bulk flow across the membrane on the transfer of phenol, and to measure the extent of back contamination of the wastewater by surfactant. Cocurrent flow of solvent and wastewater with equal transmembrane pressure differences at each end of the module were used to impose uniform bulk flows. Extractions with a range of bulk flowrates across the membrane in either direction yielded smaller overall diffusive mass transfer coefficients than the value with no bulk flow, which was approximately 2 µm/s. Back contamination of the wastewater by the surfactant was reduced by lowering the CMC of the solvent.

Glacial ice cores: A model system for developing extraterrestrial decontamination protocols

Evidence gathered from spacecraft orbiting Mars has shown that water ice exists at both poles and may form a large subsurface reservoir at lower latitudes. The recent exploration of the martian surface by unmanned landers and surface rovers, and the planned missions to eventually return samples to Earth have raised concerns regarding both forward and back contamination. Methods to search for life in these icy environments and adequate protocols to prevent contamination can be tested with earthly analogues. Studies of ice cores on Earth have established past climate changes and geological events, both globally and regionally, but only recently have these results been correlated with the biological materials (i.e., plant fragments, seeds, pollen grains, fungal spores, and microorganisms) that are entrapped and preserved within the ice. The inclusion of biology into ice coring research brings with it a whole new approach towards decontamination. Our investigations on ice from the Vostok core (Antarctica) have shown that the outer portion of the cores have up to 3 and 2 orders of magnitude higher bacterial density and dissolved organic carbon (DOC) than the inner portion of the cores, respectively, as a result of drilling and handling. The extreme gradients that exist between the outer and inner portion of these samples make contamination a very relevant aspect of geomicrobiological investigations with ice cores, particularly when the actual numbers of ambient bacterial cells are low. To address this issue and the inherent concern it raises for the integrity of future investigations with ice core materials from terrestrial and extraterrestrial environments, we employed a procedure to monitor the decontamination process in which ice core surfaces are painted with a solution containing a tracer microorganism, plasmid DNA, and fluorescent dye before sampling. Using this approach, a simple and direct method is proposed to verify the authenticity of geomicrobiological results obtained from ice core materials. Our protocol has important implications for the design of life detection experiments on Mars and the decontamination of samples that will eventually be returned to Earth.