. "4 Drilling and Sampling Technologies and the Potential for Contamination." Exploration of Antarctic Subglacial Aquatic Environments: Environmental and Scientific Stewardship. Washington, DC: The National Academies Press, 2007.
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Exploration of Antarctic Subglacial Aquatic Environments: Environmental and Scientific Stewardship
WHAT LEVELS OF CLEANLINESS ARE FEASIBLEWHEN ACCESSING SUBGLACIAL ENVIRONMENTS?
Planetary protection cleanliness requirements are achieved in a closed environment, generally in class 100K clean rooms or other facilities that have controlled environments. Spacecraft and associated hardware are cleaned, assayed to confirm bioburden levels, and maintained clean throughout building and processing. The external environment of the spacecraft is controlled up to the time of launch to prevent recontamination. While the process is dynamic due to test and rework of hardware, for the most part hardware is accessible for recleaning and assaying. Once certified as clean, mated surfaces that are no longer accessible remain so by definition unless separated due to rework or reassembly requirements. In this environment it is possible to quantify the bioburden on the spacecraft and to maintain cleanliness requirements as dictated by planetary protection protocols.
Current levels of cleanliness associated with planetary protection standards are not feasible in the open environment associated with subglacial lake exploration. While it may be possible to control the quantity of cells associated with drilling and sampling operations initially, it is not possible to control the likely transfer and distribution of cells during the drilling and sampling process. Using current technologies, it is likely that operations will transfer cells between different strata in the borehole. Drilling and sampling equipment can be precleaned prior to penetration, but the extreme depths required for drilling and the fact that hardware cannot readily be accessed for recleaning make stringent bacterial cleanliness requirements such as those implemented in space research unachievable.
In addition the water environment of the lakes facilitates cell transfer from any object that may find its way into liquid water. If the lake has unique biological ecosystems, transfer may also occur as a robotic sampling device moves from ecosystem to ecosystem. In general, cleanliness requirements will have to be addressed in terms of (1) cleaning hardware (and quantification of bacterial levels and diversity) prior to penetration, (2) maintaining hardware cleanliness levels as much as possible during penetration, and (3) designing research techniques that minimize the possibility of cell transfer between different levels in the ice and the lake bed itself.
BIOLOGICAL CONTAMINANT DETECTION
The detection of whole cells has traditionally relied on a variety of techniques including culture-based methods in which different media are used to grow organisms from a sample that can then be counted microscopically or as colonies on plates. These techniques are limited in scope because only those organisms capable of growing on a particular media formulation can be cultured, and these may constitute only a small fraction of the total community (Kämpfer et al. 1996). Microscopic counts of spores have also been used as proxies of bacteria (see Potential for Testing and Assessing Contamination: Experiences from Interplanetary Research). An important set of techniques for counting intact cells is the use of fluorescent dyes such as SYBR Gold, 4’,6-diamidino-2-phenylindole (DAPI), and acridine orange (AO). These methods use epifluorescence microscopy or flow cytometry to quantify the fluorescent-stained cells, and they are appropriate to the ongoing analysis of Antarctic glacial ice and drilling fluids for environmental monitoring and management. Application of this approach