Fig. 3.
Influence of σB and the σB-dependent yabJ-spoVG operon on excreted virulence factors. The nuclease, protease, and lipase activities of S. aureus Newman, the ΔyabJ-spoVG mutant SM148, the ΔsigB mutant MS64, and SM148 complemented with pyabJ, pspoVG, and pyabJspoVG were compared. (A) Representative agarose gels of calf thymus DNA after incubation with bacterial culture supernatants to detect nuclease activity. Whereas the DNA is not degraded with sterile LB broth (control), samples incubated with culture supernatants show different stages of DNA degradation. (B) Proteolytic activity of the strains after growth on skim milk agar plates. (C) Lipase activity monitored by hydrolysis of 4-nitrophenyl octanoate by culture supernatants. Data shown are the means ± SD of four independent experiments and are presented as percentage of lipase activity compared with that of the wild-type Newman (100%). Statistical significances between wild-type and mutant supernatants were assessed with a paired, two-tailed Student t test (*, P < 0.05; **, P < 0.01).