Abstract
NK-lysin is an antimicrobial protein produced by cytotoxic T lymphocytes and natural killer cells. In this study, we examined the biological property of a peptide, NKLP27, derived from tongue sole (Cynoglossus semilaevis) NK-lysin. NKLP27 is composed of 27 amino acids and shares little sequence identity with known NK-lysin peptides. NKLP27 possesses bactericidal activity against both Gram-negative and Gram-positive bacteria including common aquaculture pathogens. The bactericidal activity of NKLP27 was dependent on the C-terminal five residues, deletion of which dramatically reduced the activity of NKLP27. During its interaction with the target bacterial cells, NKLP27 destroyed cell membrane integrity, penetrated into the cytoplasm, and induced degradation of genomic DNA. In vivo study showed that administration of tongue sole with NKLP27 before bacterial and viral infection significantly reduced pathogen dissemination and replication in tissues. Further study revealed that fish administered with NKLP27 exhibited significantly upregulated expression of the immune genes including those that are known to be involved in antibacterial and antiviral defense. These results indicate that NKLP27 is a novel antimicrobial against bacterial and viral pathogens, and that the observed effect of NKLP27 on bacterial DNA and host gene expression adds new insights to the action mechanism of fish antimicrobial peptides.
Highlights
In the past years, wide spread use of traditional antibiotics in aquaculture has led to the emergence of diverse multidrugresistant bacterial strains that pose serious threats to public health [1,2,3]
To examine its potential antimicrobial effect, NKLP27 at different concentrations was incubated with the Gram-negative bacteria E. coli, V. anguillarum, V. harveyi, and P. fluorescence, and the Grampositive bacteria S. iniae, S. aureus, and M. luteus
The results showed that for the examined bacterial species, the Minimum inhibitory concentration (MIC) values of NKLP27 ranged between 1 mM to 8 mM, with the lowest MIC value being that against M. luteus, and the highest MIC value being against P. fluorescence (Table 1)
Summary
Wide spread use of traditional antibiotics in aquaculture has led to the emergence of diverse multidrugresistant bacterial strains that pose serious threats to public health [1,2,3]. Antimicrobial peptides (AMPs) have attracted increasing interest for their broad-spectrum antimicrobial activities and, most importantly, their unique mode of action that prevents the development of resistant variants [4,5,6,7,8]. AMPs are short, cationic peptides with an amphipathic secondary structure, by which AMPs destruct target cell membrane rapidly without the need of interaction with specific receptors [4,8]. A large number of AMPs have been identified in recent years, including hepcidin, defensins, pleurocidin, piscidin, moronecidin, misgurain, parasin, LEAP-2, and NK-lysin [11,12,13,14,15,16,17,18,19,20]
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