Identification of marker proteins for Bacillus anthracis using MALDI‐TOF MS and ion trap MS/MS after direct extraction or electrophoretic separation

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Abstract
Direct extraction of bacterial vegetative cells or spores followed by matrix‐assisted laser desorption ionization/time of flight mass spectrometry (MALDI TOF MS) has become popular for bacterial identification, since it is simple to perform and mass spectra are readily interpreted. However, only high‐abundance proteins that are of low mass and ionize readily are observed. In the case of B. anthracis spores, small acid‐soluble spore proteins (SASPs) have been the most widely studied. Additional information can be obtained using tandem mass spectrometry (MS‐MS) to confirm the identity of proteins by sequencing. This is most readily accomplished using ion trap (IT) MS‐MS. However, enzymatic digestion of these proteins is needed to generate peptides that are within the mass range of the ion trap. The use of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS‐PAGE), or other forms of electrophoresis, allows one to focus on specific proteins of interest (e. g. the high mass exosporium glycoproteins BclA and BclB) that provide additional species‐ and strain‐specific discrimination.