PNNL

Abstract

Recent experience with Bacillus spore characterization has demonstrated that protein markers can provide potentially vital identifying and bioforensic information. The masses of constitutively expressed proteins and their peptide fragments can be used to identify bacterial isolates. Protein marker mass variation information reflects the underlying amino acid sequence variation to provide complementary information to genetic sequence analysis. Protein markers (identified by mass or sequence) that are conserved or variable can be readily selected. In contrast, genetic primers, as used in PCR, target conserved genetic regions. Furthermore, protein markers are relatively stable compared to nucleic acids and may remain in samples for longer periods of time. This is important to consider when the source, age and condition of samples may vary in a forensic investigation. Examples of constitutively expressed proteins that have been extensively characterized include the exosporium BclA and BclB proteins and small acid soluble proteins (SASPs). Finally, gene expression (usually assessed at the mRNA level) can vary in response to different environmental conditions. As a result, the profile of protein markers of the organism also reflects the culture environment. Mass spectrometric tools can be used to access the same information on culture-related protein expression variation. However, unlike genetic methods, with proteomic methodology there is the potential to define exactly which medium was employed for organism growth. This potential could provide additional clues for forensic attribution