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Appl. Environ. Microbiol. doi:10.1128/AEM.01133-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Subsurface Microbial Diversity in Deep Granitic Fracture Water, Colorado, USA

Colorado School of Mines, Golden, CO 80401-1887, University of Colorado, Boulder, CO 80309, New Mexico Institute of Mining and Technology, Socorro, NM 87801, U.S. Geological Survey, Boulder, CO 80303, Colorado State University, Fort Collins, CO 80523, Climax Molybdenum Company, Empire, CO 80438

	Abstract

A microbial community analysis using 16S rRNA gene sequencing was performed on borehole water and a granite rock core from Henderson Mine; a 1000+ meter deep, molybdenum mine near Empire, Colorado. Chemical analysis of borehole water at two separate depths (1044 m and 1004 m below the mine entrance) suggests that a sharp chemical gradient exists, likely from the mixing of two distinct subsurface fluids, one metal-rich and one relatively dilute, creating unique niches for microorganisms. The microbial community analyzed from filtered, oxic borehole water indicated an abundance of sequences from iron-oxidizing bacteria (Gallionella spp.) and was compared to the community from the same borehole after two weeks of being plugged with an expandable packer. Statistical analyses with UniFrac revealed a significant shift in community structure following the addition of the packer. Phospholipid fatty acid analysis (PLFAs) suggested that Nitrosomonadales dominated the oxic borehole, while PLFAs indicative of anaerobic bacteria were most abundant in the samples from the plugged borehole. Microbial sequences were primarily represented by Firmicutes, Proteobacteria, and a lineage of sequences which did not group with any identified bacterial division; phylogenetic analyses confirmed the presence of a novel candidate division. This "Henderson Candidate Division" dominated the clone libraries from the dilute anoxic fluids. Sequences obtained from the granitic rock core (1740 m below surface) were represented by the divisions Proteobacteria (primarily the family Ralstoniaceae) and Firmicutes. Sequences grouping within Ralstoniaceae were also found in the clone libraries from metal-rich fluids, yet were absent in more dilute fluids. Lineage specific comparisons, combined with phylogenetic statistical analyses, show that geochemical variance has an important effect on microbial community structure in deep, subsurface systems.