Fig 3. Evidence for CovRS mutations as the basis for the SpeB^A- phenotype of variants selected in subcutaneous infection of mice.

(A) MGAS2221 and its rocA deletion mutant, but not its covS deletion mutant, had SpeB protease activity in overnight culture supernatant as determined by the casein hydrolysis assay. (B) Levels of SsE platelet-activating factor acetylhydrolase activity in culture supernatant at the exponential growth phase of 10 SpeB^A- variants and their 5 emm1 SpeB^A+ parent strains listed in Table 4. The SsE activity was measured using the colorimetric assay as described in the Methods.