At Site 1153, one rock sample (Sample 187-1153A-8R-1 [Piece 15A, 106-109 cm]) and two sediment samples (Samples 187-1153A-4W-2, 92-97 cm, and 7W-3, 69-71 cm) were collected to characterize the microbial community (Table T2). The rock sample is a pillow basalt fragment including both the partly altered glassy margin and the more crystalline interior. The sediment samples consist mainly of clay and differ slightly in color from dark brown (Sample 187-1153A-4W-2, 92-97 cm) to grayish brown (Sample 187-1153A-7W-3, 69-71 cm). To minimize drilling-induced contamination, the outer surface of the rock sample was quickly flamed with an acetylene torch, and the sediment samples were collected from the centers of the cores. After the sterilization, enrichment cultures and samples for DNA analysis and electron microscope studies were prepared for each sample as described in "Igneous Rocks" in "Microbiology" in the "Explanatory Notes" chapter. Aliquots of a surface seawater sample were prepared for DNA analysis as described in "Surface Seawater" in "Microbiology" in the "Explanatory Notes" chapter.
To examine the extent and type of contamination caused by drilling fluid, fluorescent microsphere tests were carried out for Cores 187-1153A-3W, 6W, and 8R (see "Tracer Test" in "Microbiology" in the "Explanatory Notes" chapter and Table T2). Smear slides from both outer and inner parts of the upper portions of the sediment cores were checked for microspheres under a fluorescence microscope, but none were detected in either the outer or inner smear slides. If the microsphere experiment had been successful, microspheres would be expected on the outer surface of the core. Because none were detected in this case, we conclude that they were flushed from the system and never reached this part of the core.
Pieces of rock from Core 187-1153A-8R were rinsed in nanopure water, the collected water was filtered, and the filters examined for the presence of microspheres under a fluorescence microscope. A thin section from the inner part of the rock was also examined under a fluorescence microscope. Microspheres were observed on the filter but not in the thin section.