CONTAMINATION CONTROLS IN BIOLOGICAL SAMPLING DURING THE 2005 ICDP-USGS DEEP DRILLING OF THE CHESAPEAKE BAY IMPACT CRATER

Knowledge of the deep subsurface biosphere on Earth is limited due to difficulties in recovering materials. Deep drilling projects provide access to the subsurface; however contamination introduced during drilling poses a major obstacle in obtaining clean samples. In order to monitor contamination during the 2005 ICDP-USGS deep drilling of the Chesapeake Bay Impact Crater (CBIC), four methods for contamination control were utilized. During the drilling process, drilling mud was infused with a perfluorocarbon chemical tracer (halon) in order to monitor penetration of mud into cores. Bags containing fluorescent microspheres of a similar size to microorganisms were introduced into the core capture device and used to mimic the ability of contaminant cells to enter the samples through fractures in the core material. Direct injection negative electrospray ionization mass spectrometry was used to analyze the acidic polar components in porewater collected from the subcore samples and samples of the drilling fluid. Specific ions unique to the drilling fluid were identified in the mass spectral fingerprints and used to determine infiltration of drilling fluid and contamination of the aqueous samples. Finally, microbial 16S rDNA clone libraries were obtained on samples of the drilling mud so that a set of potential microbial contaminants could be identified and then compared to species cultured from core samples. Together, these methods allowed us to categorise the recovered microbiological samples according to the likelihood of contamination. Twenty-two of the subcores that were retrieved were free of contamination by all the methods used and were subsequently used for microbiological culture and culture-independent analysis.