Investigation of putative antimicrobial peptides in Carassius gibel, revealing a practical approach to screening antimicrobials.

Antimicrobial peptides (AMPs) and their mimics are rapidly gaining attention as a new class of antimicrobials due to their clinical potential. AMPs are widely distributed throughout nature and participate in the innate host defense. In this study, 18 AMPs, including 3 β-defensins, 3 hepcidins, 4 liver-expressed antimicrobial peptide 2 (LEAP-2) compounds, 4 g-type lysozymes, 2 c-type lysozymes, and 2 NK-lysins, were identified from the genome of Carassius auratus by a homologous search and were further classified based on their fundamental structural features and molecular phylogeny. C. auratus AMPs were found to be ubiquitously distributed in all tested tissues and showed similar expression profiles, with the exception of β-defensins, when RT-qPCR was used to investigate the tissue distribution of AMPs in healthy Carassius gibel. In addition, the expression levels of NK-lysin genes in the tested tissues tended to be upregulated upon bacterial and viral infection when representative NK-lysins were chosen to examine their relative expression levels in various tissues. Importantly, the synthetic peptide caNKL2, which targets the functional domain of saposin B in caNK-lysins, could effectively counter Aeromonas hydrophila, Staphylococcus aureus, and Escherichia coli with minimum inhibitory concentration (MIC) values of 3-6 μg/mL, as well as inhibit the proliferation of spring viraemia of carp virus (SVCV). These results provide potential targets for antibiotic-free breeding in the aquaculture industry.