Comparative analysis of the exoproteomes of Listeria monocytogenes strains grown at low temperatures

This article presents the major differences in the exoproteomes of Listeria monocytogenes strains grown at 11 degrees C and 20 degrees C, and their comparison to 37 degrees C, the optimal temperature of growth of this foodborne pathogenic bacteria. A set of four strains previously characterized and representing the genetic diversity of the species was used. Two were virulent, of which one was persistent, and two were low virulent strains. The proteins secreted by the strains grown in minimal medium were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and identified by liquid chromatography tandem mass spectrometry. The heterogeneity among the four strains concerning the 15 major proteins detected was noticed. No clear association of exoproteome with virulence or genotype was found. Cluster analysis of the protein patterns of the strains suggests an increasing differentiation of strain response with low temperatures, highlighting the importance of the study of the exoproteomes. The main finding was the lack of some proteins in the exoproteome of the persistent strain, namely, flagellin (FlaA) and of OppA/oligopeptide ABC transporter, when compared to the other strains. In fact, these two proteins differ in abundance between strains grown at low temperature. Moreover, FlaA was the only glycoprotein identified in the exoproteomes. An attempt is made here to assess the relevance of the major exoproteins differentially detected. The investigation of the exoproteomes of other persistent and sporadic strains will allow identification of proteins involved in adaptation of particular L. monocytogenes strains to low temperatures in use throughout the food chain.