Dataset: Fluids cell counts
Deployment: MSM20-5

Whole formation fluids and bottom seawater were fixed with 3.7% formaldehyde for cell counts. Up to 19.8 ml of fixed fluids were filtered onto a 0.2 um GTBP polycarbonate filter (Millipore), stained with DAPI (4',6'-diamidino-2-phenylindole; Sigma), and counted via epiflourescent microscopy. For fluorescence in situ hybridization (FISH), cells were filtered onto 0.2 um GTTP polycarbonate filters (Millipore) and fixed with 2% paraformaldehyde, rinsed with milliQ H2O, air dried and stored at –20 degrees C until further use. Cells on filters were hybridized with HRP-labeled 16S rRNA targeted oligonucleotide probes EUB338, ARCH915 and NON338(Biomers GmbH, Ulm, Germany), and the signal was amplified as described elsewhere using Alexa 488® tyramides (Invitrogen). The permeabilization step of the protocol before probe hybridization was modified, such that the cells on the filters were first permeabilized with Proteinase K (0.005 U ul –1 in 0.05 M EDTA, 0.1 M Tris-HCl, at pH 8) for 30 minutes at 37 degrees C. Filters were then washed in 50 ml 1X PBS at room temperature, followed by a second permeabilization treatment with Lysozyme (10^6 U ml–1, in 0.05 M EDTA, 0.1 M Tris-HCl, at pH 8) for 30 minutes at 37 degrees C. After signal amplification, all cells were counterstained with DAPI and counted via epiflourescent microscopy.