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Microbial communities inhabiting recent (< or =1 million years old; Ma) seafloor basalts from the Arctic spreading ridges were analyzed using traditional enrichment culturing methods in combination with culture-independent molecular phylogenetic techniques. Fragments of 16S rDNA were amplified from the basalt samples by polymerase chain reaction, and fingerprints of the bacterial and archaeal communities were generated using denaturing gradient gel electrophoresis. This analysis indicates a substantial degree of complexity in the samples studied, showing 20-40 dominating bands per profile for the bacterial assemblages. For the archaeal assemblages, a much lower number of bands (6-12) were detected. The phylogenetic affiliations of the predominant electrophoretic bands were inferred by performing a comparative 16S rRNA gene sequence analysis. Sequences obtained from basalts affiliated with eight main phylogenetic groups of Bacteria, but were limited to only one group of the Archaea. The most frequently retrieved bacterial sequences affiliated with the gamma-proteobacteria, alpha-proteobacteria, Chloroflexi, Firmicutes, and Actinobacteria. The archaeal sequences were restricted to the marine Group 1: Crenarchaeota. Our results indicate that the basalt harbors a distinctive microbial community, as the majority of the sequences differed from those retrieved from the surrounding seawater as well as from sequences previously reported from seawater and deep-sea sediments. Most of the sequences did not match precisely any sequences in the database, indicating that the indigenous Arctic ridge basalt microbial community is yet uncharacterized. Results from enrichment cultures showed that autolithotrophic methanogens and iron reducing bacteria were present in the seafloor basalts. We suggest that microbial catalyzed cycling of iron may be important in low-temperature alteration of ocean crust basalt. The phylogenetic and physiological diversity of the seafloor basalt microorganisms differed from those previously reported from deep-sea hydrothermal systems.

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and IPOD Expedition 301 ScientistsPerfluorocarbon tracers (PFTs) are used during cruises of the Ocean Drilling Program (ODP) and Integrated Ocean Program (IODP) to measure sample contamination with drilling fluid. Drilling fluid is supplied with a constant PFT concentration that can then be detected and quantified in sediment and basalt core samples. During IODP Expedition 301, we used washing (2×) and flaming to effectively remove PFT from the exterior of basalt rocks. Near-complete removal from the exterior allowed us to demonstrate that the interior of basalts was only minutely, if at all, contaminated with drilling fluid. We examined horizontal and vertical trends in sediment core contamination. Contamination decreased greatly between the core exterior to halfway along the core radius, and slightly from halfway to the center of cores, and was generally very low in halfway and center portions. Clay cores were, on average, more contaminated than cores with fine sand. Contamination was typically highest in the two uppermost sections (sections 1 and 2) and lower below (sections 3-5). There was no relationship between depth of core origin and contamination. To determine mechanisms of contamination in halfway and interior parts of cores, we estimated the diffusive flux of PFT from the core liner towards the core center. Based on conservative estimates, we concluded that diffusion did not account for any of the PFT measured in halfway and interior parts of cores in this study. Any measurable PFT concentrations in halfway and center parts of cores were caused by advection.

During Integrated Ocean Drilling Program Expedition 301, we obtained a sample of black rust from a circulation obviation retrofit kit (CORK) observatory at a borehole on the eastern flank of Juan de Fuca Ridge. Due to overpressure, the CORK had failed to seal the borehole. Hot fluids from oceanic crust had discharged to the overlying bottom seawater and resulted in the formation of black rust analogous to a hydrothermal chimney deposit. Both culture-dependent and culture-independent analyses indicated that the black-rustassociated community differed from communities reported from other microbial habitats, including hydrothermal vents at seafloor spreading centers, while it shared phylotypes with communities previously detected in crustal fluids from the same borehole. The most frequently retrieved sequences of bacterial and archaeal 16S rRNA genes were related to the genera Ammonifex and Methanothermococcus, respectively. Most phylotypes, including phylotypes previously detected in crustal fluids, were isolated in pure culture, and their metabolic traits were determined. Quantification of the dissimilatory sulfite reductase (dsrAB) genes, together with stable sulfur isotopic and electron microscopic analyses, strongly suggested the prevalence of sulfate reduction, potentially by the Ammonifex group of bacteria. Stable carbon isotopic analyses suggested that the bulk of the microbial community was trophically reliant upon photosynthesis-derived organic matter. This report provides important insights into the phylogenetic, physiological, and trophic characteristics of subseafloor microbial ecosystems in warm ridge flank crusts.