Escherichia coli

All plasmids involved in this study were constructed with the Basic Seamless Cloning and Assembly Kit (TransGen Biotech, Beijing, China). The resulting constructs were transformed into Escherichia coli (TransGen Biotech, Beijing, China) and confirmed using PCR and sequencing (Sangon Biotech, Shanghai, China). Plasmids and primers used are listed in Table S2 and Table S3, respectively.

The fish pathogen E. piscicida (formerly known as E. tarda) has been reported previously [35 (link)]. Vibrio anguillarum and fish infectious spleen and kidney necrosis virus (ISKNV) were kindly provided by Dr. Min Zhang of Qingdao Agricultural University, and viral proliferation was reported previously [36 (link)]. Escherichia coli was purchased from Transgene (Beijing, China). Bacterial strains were cultured in Luria–Bertani broth (LB) medium at 37 °C (for E. coli) or at 28 °C (all other microbes).
The FG cell line FG-9307 was derived from the gills of Japanese flounder and maintained according to the method described by Tong [37 (link)]. Briefly, FG cells were cultured in Leibovitz’s L-15 with L-glutamine (L-15; Solarbio Science & Technology Co., Ltd., Beijing, China) supplemented with 10% bovine calf serum (BCS; HyClone, Utah, USA), 100 IU mL penicillin and 100 mg/mL streptomycin in plastic culture flasks (Corning, New York, USA) at 23 °C.