Figure 2.

(A) In acid challenge assay, log phase SS2 cultures were harvested and washed once with 0.1 M glycine buffer (pH 7.0), and then resuspended using THB with various pH values (4.0, 5.0, 6.0, and 7.0), which were achieved by adjustment with HCl. The suspensions were incubated for up to 4 h at 37°C and the numbers of surviving cells were determined by plating them on THA plates in triplicate. (B) In H₂O₂ challenge assay, log phase SS2 were pelleted, washed and resuspended in 0.1 M glycine buffer (pH 7.0). H₂O₂ was added to the cell suspension to create a final concentration of 10 mM and incubation for 15, 30, and 45 min, respectively. Then catalase was added immediately (5 mg/mL; Sigma) to the samples to inactive H₂O₂. Surviving cells were diluted appropriately, plated on THA plates. The percentage of the CFU was normalized to WT group designed as 100% (n. s, p > 0.05, **p < 0.01).