Characterization of the components of hemolysin BL from Bacillus cereus

Previously we described the partial purification of a novel hemolysin from Bacillus cereus and showed that hemolytic activity required the combined action of at least two components, called B and L to signify their cell-binding and cell-lytic roles in this activity. On further purification, as described in the present article, a combination of anion-exchange chromatography and polyacrylamide gel electrophoresis separated three proteins, B, L1, and L2 (35, 36, and 45 kDa, respectively). Individually, these proteins were inactive in hemolytic and vascular permeability assays, and combinations of B and L1 or B and L2 were either inactive or slightly active. Combinations of all three moieties produced the unique ring-shaped zone of hemolysis, a previously described characteristic of hemolysin BL, as well as edema and bluing in the vascular permeability assay. Since the vascular permeability assay is known to correlate with enterotoxicity, these results suggest that hemolysin BL is enterotoxigenic. Furthermore, the molecular weights and isoelectric point values of the hemolysin BL components are consistent with those described by others for the multicomponent diarrheal enterotoxin of B. cereus. Immunofluorescent staining of B-treated erythrocytes confirmed that B binds to cells as an initial step required before the L components can act to cause cell lysis.