Identification of stress-induced proteomic changes in a virulent Listeria monocytogenes strain

Adaptive stress response is a key factor for the survival of Listeria monocytogenes in foods and food environments. This study aims to investigate the immunogenic proteins (IP) encoded by L. monocytogenes ST7 following exposure to environmental stressors. To give a better understanding of the role of the proteins expressed under stress conditions, L. monocytogenes cells were cultivated at 37 °C, pH 7.0, NaCl 0.5 % – optimal condition (C1) – and 12 °C, pH 5.5, NaCl 7 % (C2), and were collected at late exponential growth phase. The proteins were extracted by enzymatic reagents, precipitated, solubilized, and then quantified by BCA method. Proteins identification was performed by shot-gun nLC-MS/MS approach, filtering and selecting only those proteins identified with at least 2 peptides against L. monocytogenes Uniprot database. The IP prediction was obtained by mean of sublocalization and immunogenic software. Gene enrichment analysis was performed by STRING v11.05. To face stress environmental conditions, L. monocytogenes encoded for proteins associated to cell wall (lmo1090, lmo1091, lmo0933, lmo2550, lmo0497), which might have an impact on hostpathogen interaction as Internalin A (InlA) and Inhibitor apoptosis (Iap) proteins, well known virulence factors involved in host cell adhesion. Moreover, these factors were absent in optimal condition (C1), in which instead a sugar uptake cluster (lmo0097, lmo0098, lmo0781, lmo0782, lmo0099, fruA) was identified. This cluster was positively regulated by Sigma B (σB) virulence and Accessory gene regulator (Agr), which are associated to quorum sensing system and cell survival. Our findings suggest that these proteins may be involved in the adaptation of L. monocytogenes to environmental stress factors and may be important to explain the general stress response and the pathogenesis of L. monocytogenes.