Rapid Chemical Digestion of Small Acid-Soluble Spore Proteins for Analysis of Bacillus Spores

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Abstract
A method for the rapid identification of Bacillus spores is proposed, based on the selective release and chemical digestion of small, acid-soluble spore proteins (SASPs). Microwave-assisted acid hydrolysis of SASPs from B. anthracis str. Sterne and B. subtilis str. 168 was accomplished in a single step requiring only 90 s of heating. The peptide products of the chemical digestion were identified by postsource decay sequencing with a MALDI-TOF-MS equipped with a curved-field reflectron. The specificity of the observed SASP peptides was evaluated using a cross-species sequence search. The incomplete nature of the acid digestion under these conditions allowed detection of the digest products along with the proteins from which they originated, which increased species identification confidence. The feasibility of this approach for the rapid identification of Bacillus species was further demonstrated by analyzing a mixture of B. subtilis str. 168 and B. anthracis str. Sterne spores.