Bacteriophage Isolation and Purification

About 50 ml of microbial biomass was first disrupted by pottering on ice to free the bacteriophages. To digest non-viral DNA and RNA, DNase I (Thermo Scientific, final concentration 1U/ml), and RNase A (Thermo Scientific, final concentration 5U/mL) treatments were simultaneously performed for 1 h at 37°C. The sample volume was divided in 2 ml Eppendorf tubes and PEG 8000 precipitation was performed as described previously (Guo et al., 2012 (link)). The sample was centrifuged for 30 min at 2000 × g and the obtained pellet was resuspended in MSM buffer. PEG 8000 was separated from the viral particles as described previously (Colombet and Sime-Ngando, 2012 ). In addition, to lower the salt concentration, the supernatant containing free phages was extensively washed with MSM buffer in spin columns (Vivaspin, GE Healthcare, 10,000 MWCO) at 2500 × g and 4°C using an Allegra X-15R Centrifuge (Beckman Coulter) to a final concentration of 20 mM KCl. The sample was stored at 4°C until further analyses.