Fig. 2.

Positive-ion MALDI-TOF mass spectra of SCWP-derived oligosaccharides (OSs) isolated from different Bacillus strains. (A) B. anthracis Ames; (B) B. cereus G9241; and (C) B. cereus 03BB102. The OSs from B. cereus strain 03BB87 gives identical results as shown for strain G9241. Ions are sodiated species of the form [M + Na]⁺¹. In all spectra, the molecular ion with mass of 1136 represents the sodiated MM of the hexasaccharide repeating unit (Hex₃HexNAc₃). The molecular ion with mass of 974 indicates the presence of this repeating unit less one hexose (i.e. Gal). The next cluster of ions with mass 2232 represents the dimer of the hexasaccharide, and ions with m/z 2070 and 1908 are, respectively, one and two Gal units less than the dimer. The SCWP from all B. cereus and B. anthracis strains showed the presence of these same ions, indicating the presence of conserved structural features. However, ions with more, as well as less, Gal substitutions were also observed in the B. cereus SCWP compared with B. anthracis SCWPs, indicating additional heterogeneity of the secondary cell wall structures in these pathogenic B. cereus strains. The B. cereus 03BB102 SCWP shows additional complexity, with increments corresponding to (Hex₁HexNAc₃), to be described in a separate report.