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doi:10.2204/iodp.proc.311.104.2006

Microbiology

Site U1326 is located along the transect of sites established during Expedition 311 across the northern Cascadia accretionary prism at the westernmost uplifted ridge of the accretionary prism. It was the last site sampled for microbiology. Efforts continued to obtain live anaerobic methane oxidizers, potentially unknown gas hydrate–associated microbial communities, high pressure adapted microorganisms, and methanogens. Subsampling for direct cell counts and biological contamination tests continued at this site.

Microbiological sampling

Sampling from the mudline (Sample 311-U1326C-1H-1, 0–3 cm) in Hole U1326C and the deepest core (Sample 311-U1326D-20X-1, 70–80 cm; 263 mbsf) in Hole U1326D targeted microorganisms for aerobic and anaerobic high-pressure culturing.

Methanogenesis can occur in most anaerobic environments, but it becomes the major metabolic strategy when other electron donors such as nitrate, Fe(III), and sulfate are depleted. We sampled regularly downhole to below the depth of the predicted BSR to quantify methanogenesis in these sediments (see "Microbiology" in the "Methods" chapter).

Contamination tests

Contamination tests at previous sites had verified that the interior of APC cores and the center of biscuits in XCB cores yielded samples with low amounts of exogenous microbial contamination. At this site we focused contamination tests on sand layers, gas hydrate–bearing sediments, and shallow APC cores where soupy texture is common.

Perfluorocarbon tracers

Samples for perfluorocarbon tracers and fluorescent microsphere analyses were taken immediately from the ends of APC whole-round cut sections on the catwalk. Extra sediment samples for microsphere analysis were collected from split cores in the core laboratory because it was possible to differentiate between sand layers, biscuits, and drilling slurry. Sediment samples associated with gas hydrate were collected from the ends of whole-round sections when the presence of gas hydrate was indicated by the data collected on the catwalk using the IR camera. Samples were analyzed as described and the raw data are presented in Table T9.

Fluorescent microspheres

We detected very small but nonzero numbers of fluorescent microspheres in the interior of the mudline APC core, which was very soupy at this site. Tests on sand layers, which were widely distributed at this site, showed that the interiors of sand layers were possibly contaminated with microspheres but at a very low level. One of the gas hydrate–bearing samples indicated that the interior of the sediment was contaminated with the microspheres at a very low level.

Shipboard analysis

Samples were taken from the top (Sample 311-U1326C-1H-1, 0–3 cm) and bottom (Sample 311-U1326D-20X-1, 70–80 cm; 263 mbsf) of the sedimentary section for inoculation of enrichment cultures targeting high-pressure adapted heterotrophic and sulfate-reducing microorganisms. Samples were maintained at low temperature, and dilution series were inoculated to culture for microorganisms at 55.1 MPa and 4°C. Cultures for sulfate reducers required preparation in the anaerobic chamber and were fed formate, acetate, or lactate as a carbon source.

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