Abstract

β-defensins (BDs) are a group of cysteine-rich cationic antimicrobial peptides and play important roles in the first line of defense against infection. In this study, the expression and antibacterial activities of three grass carp ( Ctenopharyngodon idella ) ( Ci ) β-defensin (BD) peptides were comparatively investigated. Expression analysis reveals that CiBD1-3 were constitutively expressed in tissues, with the highest expression detected in the skin. The CiBD-1 transcripts were more abundant than Ci BD-2 and Ci BD-3. In the primary head kidney leukocytes, Ci BDs were induced by PHA , LPS, poly(I:C) and cytokines such as IL-1β and IFN-γ. In vivo challenge of fish with Aeromonas hydrophila resulted in the up-regulation of CiBDs in the head kidney and hindgut . To determine the biological activities, recombinant Ci BD proteins were produced in the HEK293-F cells and purified for the minimum inhibitory concentration assay. It was found that all three recombinant Ci BD proteins were effective to inhibit the growth of Gram-negative fish bacterial pathogens including Aeromonas hydrophila, Edwardsiella tarda , Flavobacterium columnare and Klebsiella pneumoniae and Gram-positive Staphylococcus aureus . Ci BD-2 and Ci BD-3 were more effective than Ci BD-1. Our results demonstrate that all the three Ci BDs have broad antibacterial activity against fish bacterial pathogens.