A novel antimicrobial peptide Spasin141-165 identified from Scylla paramamosain exhibiting protection against Aeromonas hydrophila infection

Aeromonas hydrophila is a widely distributed Gram-negative waterborne pathogen responsible for large-scale outbreaks of hemorrhagic septicemia in fish, causing severe economic losses to the global aquaculture industry. In view of few therapeutic drugs currently available for use in aquaculture and the emergence of multidrug-resistant A. hydrophila, there is an urgent need to develop new antimicrobial agents as an alternative to antibiotics. Antimicrobial peptides (AMPs) have strong antimicrobial effects and unique machanisms of action, and are not easy to induce bacterial resistance, making them an ideal alternative to antibiotics. In this study, we identified a new functional gene from marine crab Scylla paramamosain, named Spasin, which encodes a mature peptide of 240 amino acids and expressed widely in various tissues of crabs. Notably, a truncated peptide Spasin141–165 derived from Spasin, showed potent and broad-spectrum antibacterial and antifungal activity at minimum inhibitory concentrations (MICs) ranged from 0.75 μM–48 μM, which is a novel AMP. It effectively killed S. aureus and A. baumannii within 2 h and 90 min, respectively. Importantly, it is not toxic to HEK-293 T, RAW 264.7, and ZF4 cell lines. Mechanistic studies showed that addition of 8 μg mL−1 lipoteichoic acid or lipopolysaccharides decreased bacterial susceptibility to Spasin141–165. In addition, Spasin141–165 altered the permeability of the inner and outer cell membranes, and resulted in the release of ATP and the accumulation of intracellular reactive oxygen species. Notably, Spasin141–165 significantly increased the survival rate of zebrafish infected with A. hydrophila, redcued the bacterial load in the spleen, and effectively inhibited the expression of inflammation-associated factors (e.g., IL-1β, TNF-α, etc.). Taken together, Spasin141–165 is a potential antibacterial agent for the treatment of A. hydrophila infections in aquaculture and a promising antibiotic alternative.