FIG 4.

Proteolytic activities of wild-type and ΔgldN mutant cells. Exoproteolytic activities of F. psychrophilum wild type (WT), ΔgldN mutant, and ΔgldN mutant complemented with pBFp4. (A) Stationary-phase cultures were spotted on TYESG agar supplemented with casein (7.5 g/liter), and proteolytic activity was visualized as clearing zones around the bacterial growth after incubation at 18°C for 4 days. (B) Proteolytic activity measured using azocasein as a substrate. Cells were grown in TYESG broth at 18°C with shaking. Proteolytic activity was measured in cell-free supernatants from each strain at different stages of growth. The results of three experiments are presented (values and error bars are means and standard deviations, respectively). Solid lines, OD₆₀₀, indicating growth; dashed lines, proteolytic activity units.