Bacteria abundance measured on water bottle samples during HUDSON cruise HUD97/9@en

Samples for enumeration of bacterial abundance were drawn from Niskin bottles and immediately preserved in 20 mL glass scintillation vials with 0.2 µm filtered (Millex-GS, Millipore Corp.) formalin (2% final concentration). Preserved samples were stored dark in a refrigerator. Each sample was poured over triplicate polycarbonate membranes (0.2 µm black Nuclepore) underlain by pre-wetted backing filters (Sartorius #11306) which aid in distributing cells in an even manner on the Nuclepore surface. Cells were stained for 10 minutes with DAPI at a final concentration of 2 µg/ml and then drawn through the filters at a vacuum pressure of about 150 mm Hg. The filters were examined by epifluorescence microscopy (Leitz Orthoplan) under ultraviolet excitation from a mercury arc lamp (HBO 100W).用于细菌丰度计数的样品取自尼斯金采水器（Niskin bottles），并立即转移至20 mL玻璃闪烁瓶中，加入经0.2 µm过滤（Millex-GS，密理博公司（Millipore Corp.））的福尔马林，使其终浓度达到2%。经固定的样品于暗处冰箱内储存。将每份样品倾倒至三份置于预湿支撑滤膜（赛多利斯#11306，Sartorius #11306）上方的聚碳酸酯滤膜（0.2 µm黑色Nuclepore滤膜）上进行过滤，该支撑滤膜可帮助细胞在Nuclepore滤膜表面均匀分布。细胞用终浓度为2 µg/mL的DAPI (4',6-二脒基-2-苯基吲哚)染色10分钟，随后以约150毫米汞柱（mm Hg）的真空压力抽滤通过滤膜。采用Leitz Orthoplan型落射荧光显微镜（epifluorescence microscopy），搭配100W汞弧灯（mercury arc lamp，HBO 100W）作为紫外激发光源，对滤膜进行观测计数。