Radiation sensitivity of Bacillus cereus with and without a crystalline surface protein layer

The radiation sensitivity of four strains of Bacillus cereus was investigated with attention to bacterial surface structure. All four strains were sensitive to radiation with gamma rays (D(10)=0.4 kGy). No crystalline surface protein layer could be detected on the cell surface. When cultured on solid media, an S-layer covered the cells of the two strains, and they were 2.6 times as resistant to radiation as the two reference strains without an S-layer. In SDS-PAGE, a major 97-kDa band from the resistant strains from plate cultures was replaced by a ca. 85-kDa protein band in samples from broth cultures. Electron microscopy, SDS-PAGE, Western blot and fluorescent antibody staining indicated that the higher resistance to radiation of the clinical strains from plate cultures was associated with the presence of the S-layer on the cell surface.