Insight into the core and variant exoproteomes of Listeria monocytogenes species by comparative subproteomic analysis

While Listeria monocytogenes is responsible for listeriosis, it is also a saprophytic species with exceptional survival aptitudes. Secreted proteins are one of the main tools used by bacteria to interact with their environment. In order to take into account the biodiversity of L. monocytogenes species, exoproteomic analysis was carried out on 12 representative strains. Following 2-DE and MALDI-TOF MS, a total of 151 spots were identified and corresponded to 60 non-orthologous proteins. To categorize and analyze these proteomic data, a rational bioinformatic approach predicting final subcellular localization was carried out. Fifty-two out of the 60 proteins identified (86.7%) were indeed predicted as localized in the extracellular milieu (gene ontology (GO): 0005576). Most of them (65.4%) were actually predicted as secreted via the Sec translocon. Comparative analysis allowed for proteins found in all or only in a subset of L. monocytogenes strains to be defined. While the core exoproteome included most proteins related to bacterial virulence, cell wall biogenesis, as well as proteins secreted by unknown pathways, a slight variation in the protein members of these categories were observed and constituted the variant exoproteome. This investigation resulted in the first definition of the core and variant exoproteomes of L. monocytogenes where corollaries on bacterial physiology are further discussed.