Low-Temperature Proteomic Remodelling Reveals Distinct Metabolic Profiles in Listeria monocytogenes Strains Belonging to Clonal Complexes CC1 and CC9

Background: Persistence under refrigeration is an important feature of Listeria monocytogenes, yet the molecular basis underlying lineage-specific differences in adaptation to these conditions remains poorly understood. In this study, we investigated proteomic difference between two L. monocytogenes strains belonging to epidemiologically distinct clonal complexes (CCs), CC9 and CC1, which represent a food-associated, hypovirulent lineage and a hypervirulent, human-associated lineage, respectively. Methods: Cultures of the two L. monocytogenes strains were grown at 10 °C and analysed by label-free quantitative (LFQ) mass spectrometry. Identified proteins were subjected to in silico prediction of antigenic and virulence-associated properties, subcellular analysis, and functional annotation using KEGG pathways. Results: A total of 915 proteins were identified, of which 703 were predicted in silico to be antigenic and/or virulence-associated. Among these, 165 were detected only in the CC9 strain, 49 only in the CC1 strain, and 489 were shared by both strains. The shared protein complement included FlgE, Lmo0723, Dps, PrfA, and RecA, reflectin conserved functions related to motility, stress response, virulence regulation, and genome maintenance. Functional annotation assigned a larger number of proteins to metabolic and cellular pathways in the CC9 strain, largely reflecting the higher number of proteins detected only in this strain, whereas in the CC1 strain carbohydrate metabolism accounted for a larger proportion of the annotated proteins. Quantitative analysis further identified 19 proteins with increased abundance and 66 with decreased abundance in CC1 relative to CC9. Conclusions: These findings reveal distinct proteomic signatures in the CC1 and CC9 strains during growth at low temperature and suggest that their contrasting metabolic and stress-response profiles may be related to their different ecological and pathogenic characteristics. Validation in a larger panel of strains is required to establish whether these features are lineage-associated.