To test the effect of hydrogen peroxide (H2O2) on growth of each strain, we used a previously reported method [28 (link)] with slight modification. Each strain was cultured in XOM2 broth medium at 28 °C with shaking until the population reached 3.5 × 108 CFU/mL. Then, 200 μL of each cell culture was mixed with 20 mL PSA medium (1.0% agar) containing appropriate antibiotics and poured into a Petri-dish (90 × 15 mm, SPL life science, Seoul, South Korea). After solidification, a 6-mm-diameter sterilized Whatman paper disc was placed on the center of the plate, and then 5 μL of H2O2 (1 mM and 10 mM) was dropped onto the paper disc. Halo zone formation by H2O2 on the PSA plate was monitored, and the diameter was measured after 3 days of incubation at 28 °C.
Survivability of each strain against ROS was tested as described previously [19 (link)]. Each strain was incubated in XOM2 broth medium at 28 °C with shaking to 3.5 × 108 CFU/mL. These cells were transferred to fresh XOM2 containing H2O2 (0, 1, or 10 mM) at a density of OD600 = 0.2 and then shaken at 200 rpm and 28 °C for 6 h. The cells were spotted after serial dilution onto PSA plates containing appropriate antibiotics to count cell number.
Survivability of each strain against ROS was tested as described previously [19 (link)]. Each strain was incubated in XOM2 broth medium at 28 °C with shaking to 3.5 × 108 CFU/mL. These cells were transferred to fresh XOM2 containing H2O2 (0, 1, or 10 mM) at a density of OD600 = 0.2 and then shaken at 200 rpm and 28 °C for 6 h. The cells were spotted after serial dilution onto PSA plates containing appropriate antibiotics to count cell number.
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