Microporous membrane

Chromatographic pure methanol (Fisher Scientific, USA); chromatographic purified water (DUKSAN, Korea); cell culture dish, cell culture bottle, 96-well cell culture plate (Corning, USA); ultra-clean workbench (Thermo Scientific, USA); pipetting gun (Eppendorf, Germany); inverted phase contrast microscope (OLYMPUS, Japan); microporous membrane (0.22 μm, Millipore, USA); microplate reader (BioTek, USA); Antifade Polyvinylpyrrolidone Mounting Medium (Biyuntian Biotechnology Co., Ltd., Shanghai, China); microporous membrane (0.22 μm, Millipore, USA); Western blot electrophoresis (Bio-Rad, USA); Western blot electric converter (Bio-Rad, USA); Decoloring shaker (3D, China); Vortex oscillator (SCILOGEX, USA).

The physical parameters of the surface freshwater were measured in situ using a multiprobe instrument (HQd Portable Meter, Edition 6, HACH, USA) before sample collection. The measured parameters included pH, electrical conductivity (EC), and DO. Moreover, TN, TP, COD, nitrate nitrogen (NO₃^–-N) and ammonia nitrogen (NH₄⁺-N) were measured by a water quality analysis system (DRB200 and DR3900, HACH, USA). The biochemical oxygen demand (BOD₅) and chlorophyll-a (Chla) concentration were determined with the HJ505-2009 and HJ897-2017 methods (Ministry of Ecology and Environment of the People’s Republic of China, 2009 , 2017 ), respectively. The freshwater samples were passed through microporous membranes with a pore size of 0.22°μm and a diameter of 50 mm (Millipore, USA), and microbiological analysis was then conducted on microorganisms attached to the membranes. The microbial filter membrane samples were stored at −80°C until DNA extraction.