FIG. 6.

Analyses of supernatants from a VtpA-deficient mutant of V. tubiashii strain RE22. Protease (A) and hemolysin (B) production, as well as toxicity to oyster larvae (C), was compared to that of the wild-type strain. Although the mutant strain, but not the wild-type strain, was grown in the presence of 50 μg/ml kanamycin, all cells were harvested at an OD₆₀₀ of approximately 3.0. For the toxicity assay, filter-sterilized supernatants were added to a final concentration of 0.5%. The error bars indicate standard deviations (n = 3). Data for proteolytic and hemolytic activities were evaluated by Student's t test (*, P < 0.01 compared with the wild type). Data for larval mortality were evaluated by chi-square test (*, P < 0.05 compared with the wild type).