Figure 3.

Impact of mutating individual protease genes/operons. Proteolytic activity was assessed in FPR3757 (WT) with and without addition of the indicated protease, its sarA mutant, and derivatives of the sarA mutant with mutations inactivating the indicated protease genes. Top panel: To ensure the use of physiologically relevant amounts of purified proteases in the context of the amounts produced by the isogenic sarA mutant, each purified protease was examined individually at a concentration of 250 nmol/L, which was the highest concentration used in our protease add-back experiments. Bottom panels: The protease phenotype of the WT strain was compared to that of its sarA mutant carrying mutations in the indicated protease genes. As discussed in the text, the sspA mutation is polar, thus eliminating production of both SspA and SspB. Purified proteases were also included as additional controls.