At Site 1158 two rock samples (Samples 187-1158A-2R-1 [Piece 8, 34-37 cm] and 187-1158C-2R-1 [Piece 10, 54-57 cm]) were collected to characterize the microbial community inhabiting this environment (Table T2). Both samples were pillow basalt fragments composed of crystalline basalt only (see "Igneous Petrology"). To sterilize them, the outer surfaces of the rock samples were quickly flamed with an acetylene torch, and enrichment cultures and samples for high-pressure enrichment, DNA analysis, and electron microscope studies were prepared (see "Igneous Rocks" in "Microbiology" in the "Explanatory Notes" chapter).
To evaluate the extent and type of contamination caused by drilling fluid, fluorescent microsphere tests were carried out for both rock cores. Surface seawater was collected for DNA characterization (Table T2; also see "Tracer Test" and "Surface Seawater" in "Microbiology" in the "Explanatory Notes" chapter). Pieces from each core were rinsed in nanopure water, the collected water was filtered, and the filters were examined for the presence of microspheres under a fluorescence microscope. Thin sections were used to examine the extent of contamination inside the samples. Microspheres were detected on the filters; in the thin sections microspheres were found both inside fractures and on the thin-section surface. All were located close to the thin-section margins, with the exception of one microsphere that was observed in a large fracture in the thin-section center (Section 187-1158A-2R-1). Five microspheres were observed in thin sections from Core 187-1158A-2R and 13 from Core 187-1158C-2R. Of these, 12 were in a single crack.