FIG. 1.

Production of caseinolytic protease during Y. ruckeri growth. Cells were grown in NB medium, and at different incubation times 120 μl of the cell-free supernatants was used to measure the caseinolytic activity, with azocasein used as a substrate. (A) Absorbance at 600 nm as a measure of cell density. (B) Caseinolytic activity. Symbols: ○, Y. ruckeri wild-type strain; ■, CS1 mutant; and ▴, E1 mutant.