ASSESSING THE EFFECTS OF SAMPLING AND LONG-TERM STORAGE ON MICROBIAL LIPID BIOMARKER DISTRIBUTION IN DEEP SUBSURFACE MARCELLUS SHALE CORES

This study investigates the effects of sampling and storage conditions on subsurface microbial community using phospholipid fatty acids (PLFAs) and diglyceride fatty acids (DGFs) analyses. We collected core samples at similar intervals from two Marcellus Shale wells (WV 6 and MSEEL) at depths of about 2.5 km in Monongalia County, West Virginia. The WV 6 samples were collected and stored at room temperature for a long period of time while the samples from MSEEL were obtained from fresh cores collected using pertinent microbial sampling protocols and stored at -80°C till analysis. The PLFA’s and DGFA’s were extracted from samples of both cores and analyzed using the gas chromatography-mass spectrometry (GC-MS). The total yield and variety of the PLFA and DGFA profiles were examined as fatty acid methyl esters (FAMEs). The variety of individual and functional group biomarkers were higher in the freshly collected MSEEL core samples compared to the WV 6 core samples that were stored under room temperature conditions for several years. The lipid profiles in the MSEEL core samples consisted of normal saturated, monounsaturated, polyunsaturated, branched, oxiranes, and hydroxyl fatty acids while the WV 6 core samples consisted of normal saturated, monounsaturated, polyunsaturated, and hydroxyl fatty acids. We also observed an increase in lipid biomarker concentration in the MSEEL samples compared to WV 6 samples. The absence of some of the stress indicative biomarkers like keto-, and oxiranes in the WV 6 after storage suggested that these biomarkers adapted to changing environmental conditions associated with sampling, handling, and storage. Our results indicate the plausible changes that can take place in microbial biomarker distribution and the important role that appropriate sample collection, handling, and storage have on the efficient characterization of subsurface microbial communities.