FIG 3.

The stringent response modulates GBS βHC expression and hemolytic activity. (A) A909 and 10/84 WT and SR mutants were grown overnight in new Granada medium with appropriate antibiotic selection. The cultures were normalized for OD₆₀₀ and volume, pelleted, resuspended in 100 μl PBS, and photographed in a 96-well plate. (B) A909 ΔrelA shows decreased hemolysis relative to the results for the WT and ΔrelA+pDC123:relA strains. (C) WT A909 grown under SR-activating conditions with supplemental SHX shows enhanced hemolysis over bacteria grown in TSB or A909 ΔcylE, which does not produce βHC. All hemolysis experiments were performed in triplicate and repeated at least twice. The percentage of hemolysis is relative to the result for a 1% Triton X-100 positive-control solution. Histograms show mean values, with error bars illustrating standard errors of the means. ***, P < 0.005, and ****, P < 0.0001, t test with Bonferroni correction for multiple comparisons.