FIG 3 .

Effect of purified Stx2 on the survival of axenically growing wild-type and NP1 mutant Tetrahymena cells at various temperatures. Purified Stx2 holotoxin or BSA (40 ng/ml) was added to 10⁴/ml Tetrahymena cells cultured as described in Materials and Methods at 30°C (A) or 37°C (B). The number of live Tetrahymena cells was determined after 6 h of incubation. Data are presented as the number of live Tetrahymena cells after incubation relative to the number of live Tetrahymena cells at the start of incubation. Error bars represent standard deviations from three or more independent experiments, with each experiment comprising a minimum of three individual measurements. *, P < 0.01; **, P < 0.001.