Characterization of Residual Medium Peptides from Yersinia pestis Cultures

Here we demonstrate that when Yersinia pesitis is grown in laboratory media, peptides from the medium remain associated with cellular biomass even after washing and inactivation of the bacteria by different methods. These peptides are characteristic of the type of growth medium and of the manufacturer of the medium, reflecting the specific composition of the medium. We analyzed biomass-associated peptides from cultures of two attenuated strains of Yersinia pestis [KIM D27 (pgm-) and KIM D1 (lcr-)] grown in several formulations of 4 different media (tryptic soy broth (TSB), brain–heart infusion (BHI), Luria–Bertani broth (LB), and glucose (G) medium) made from components purchased from different suppliers. Despite the range of growth medium sources and the associated manufacturing processes used in their production, a high degree of peptide similarity was observed for a given medium recipe; however, notable differences in the termination points of select peptides were observed in media formulated using products from some suppliers, presumably reflecting the process by which a manufacturer performed protein hydrolysis for use in culture media. These results may help explain the presence of peptides not explicitly associated with target organisms during proteomic analysis of microbes and other biological systems that require culturing. While the primary aim of this work is to outline the range and type of medium peptides associated with Yersinia pestis biomass and improve the quality of proteomic measurements, these peptides may also represent a potentially useful forensic signature that could provide information about microbial culturing conditions.