New insight into the biological activity of Salmo salar NK-lysin antimicrobial peptides.

NK-lysin is a potent antimicrobial peptide (AMP) with antimicrobial activity against bacteria, fungi, viruses, and parasites. NK-lysin is a type of granulysin, a member of the saposin-like proteins family first isolated from a pig's small intestine. In previous work, for the first time, we identified four variants of nk-lysin from Atlantic salmon (Salmo salar) using EST sequences. In the present study, we reported and characterized two additional transcripts of NK-lysin from S. salar. Besides, we evaluated the tissue distribution of three NK-lysins from S. salar and assessed the antimicrobial, hemolytic, and immunomodulatory activities and signaling pathways of three NK-lysin-derived peptides. The synthetic peptides displayed antimicrobial activity against Piscirickettsia salmonis (LF-89) and Flavobacterium psychrophilum. These peptides induced the expression of immune genes related to innate and adaptive immune responses in vitro and in vivo. The immunomodulatory activity of the peptides involves the mitogen-activated protein kinases-mediated signaling pathway, including p38, extracellular signal-regulated kinase 1/2, and/or c-Jun N-terminal kinases. Besides, the peptides modulated the immune response induced by pathogen-associated molecular patterns (PAMPs). Our findings show that NK-lysin could be a highly effective immunostimulant or vaccine adjuvant for use in fish aquaculture.

Proteomic analysis of Listeria monocytogenes exposed to free and nanostructured antimicrobial lipopeptides.

In this work, the effect of antimicrobial lipopeptide P34 on Listeria monocytogenes was evaluated for the first time through a proteomics approach. Bacteria were treated with sub-lethal doses of peptide P34 (F-P34) and P34 encapsulated into nanoliposomes (N-P34), while empty nanoliposomes (NE) and fresh buffer were used as controls. The proteomic analysis allowed the detection of one group of proteins commonly differentially represented in response to free and encapsulated P34 exposure. A second group of proteins was found to be exclusively differentially represented after exposure with encapsulated P34 only. The antimicrobial peptide P34 caused a significant downregulation of proteins associated with the transport of manganese and the over-representation of proteins related with iron transport in L. monocytogenes. In addition, reduction of stress tolerance proteins related to the σB and VirR regulons, together with the modulation of phosphoenolpyruvate phosphotransferase systems (PTS) for sugar transport were observed. The sugar and oligopeptide transporters regulated by antimicrobial action may influence the key virulence factor PrfA, reducing the pathogenicity of this microorganism.