Nisin influence on the expression of Listeria monocytogenes surface proteins

In this work, a comparative analysis of the peripheral cell component (PCC) proteins of Listeria monocytogenes was carried out. The study was conducted on two set of samples consisting of bacteria treated with sub-lethal concentration of nisin and untreated bacteria as control. PCC proteins were extracted by Tris-Urea-EDTA treatment and then subjected to trypsin digestion and mass spectrometry analysis. The whole cell proteome was analyzed through label-free quantitative proteomics approach. Proteomic analysis was carried out using OrbiTrap Mass Spectrometer coupled to nanoflow liquid chromatography. The treatment with sub-lethal nisin concentration resulted in 62 up regulated and 97 down regulated proteins compared to untreated samples. Using PSORTb 3.0, 19 and 18 surface proteins were detected among the up regulated and down regulated proteins, respectively. Proteins related with increased biofilm formation by L.monocytogenes, such as moonlight proteins of the pyruvate dehydrogenase complex and flagellin-related proteins, were identified as up regulated surface proteins. Proteins associated with virulence of L.monocytogenes, including listeriolysin O, internalin B and actin assembly-inducing protein, were detected among the down regulated proteins. To confirm proteomics data, increased production of biofilm was experimentally confirmed in nisin-treated cells through crystal violet method. BIOLOGICAL SIGNIFICANCE: Proteosurfaceomics can be defined as the "omics" science applied to the proteins of the peripheral cell component (PCC). The surface proteins of Listeria monocytogenes, an important foodborne pathogen were investigated after treatment with nisin, a bacteriocin approved as a natural food preservative by regulatory agencies. Recent cases of nisin tolerance by Listeria spp. were documented, and deeper studies on the molecular process behind the bacterial survival may help in both understanding the development of tolerance process and comparing nisin effect with other antimicrobial compounds.