PrfA activation in Listeria monocytogenes increases the sensitivity to class IIa bacteriocins despite impaired expression of the bacteriocin receptor.

Background: The scope of the present work was to characterize the activity of class IIa bacteriocins in Listeria (L.) monocytogenes cells that constitutively express an activated form of PrfA, the virulence master regulator, since bacteriocin sensitivity was only characterized in saprophytic cells so far. The mannose phosphotransferase system (Man-PTS) has been shown to be the class IIa bacteriocin receptor in Listeria; hence, special attention was paid to its expression in virulent bacteria.

Methods: L. monocytogenes FBprfA* cells were obtained by transconjugation. Bacterial growth was studied in TSB and glucose containing-minimal medium. Sensitivity to antimicrobial peptides was assessed by killing curves. Membranes of L. monocytogenes FBprfA* cells were characterized using proteomic and lipidomic approaches.

Results: The mannose phosphotransferase system (Man-PTS) was downregulated upon expression of PrfA*, and these cells turned out to be more sensitive to enterocin CRL35 and pediocin PA-1, while not to nisin. Proteomic and lipidomic analysis showed differences between wild type (WT) and PrfA* strains. For instance, phosphatidic acid was only detected in PrfA* cells, whereas, there was a significant decline of plasmalogen-phosphatidylglycerol in the same strain.

Conclusions: Our results support a model in which Man-PTS acts just as a docking molecule that brings class IIa bacteriocins to the plasma membrane. Furthermore, our results suggest that lipids play a crucial role in the mechanism of action of bacteriocins.

General Significance: This is the first demonstration of the link between L. monocytogenes virulence and the bacterial sensitivity toward pediocin-like peptides.