Abstract In order to obtain high-quality microbial samples from the hadal zone, which has a depth of over 6,000 m, a full-ocean-depth sampler with the function of in-situ filtration and preservation was developed. A flow pump and several membrane filters were used for in-situ
filtration under the sea. With a multistage filtering structure, the microbes can be initially screened according to their sizes. To avoid the degradation of microbial ribonucleic acid (RNA), a special structure was designed to inject the RNAlater solution into the samples immediately after
the filtration. The sampler was tested in our laboratory and deployed during Mariana TS-15 in 2019. It was installed on a hadal lander of Shanghai Ocean University and deployed at MBR02 (11.371°N, 142.587°E, 10,931 m) in the Mariana Trench. A total of 20 L of in-situ seawater was filtered,
and membranes with pore sizes of 3 and 0.2 μm were preserved. The study is expected to provide important support for the establishment of a hadal microbial gene pool.