A coral peptide with bactericidal activity against a global marine pathogen, Vibrio coralliilyticus.

Rising seawater temperatures weaken coral immunity and increase the virulence of the coral pathogen Vibrio coralliilyticus. Here, we identified digitiferin, an antimicrobial peptide (AMP), in the coral, Acropora digitifera. Recombinant digitiferin showed antibacterial activity against both Gram-positive and -negative bacteria. A 3D structural model and microscopic observations revealed that digitiferin damages bacterial surfaces. However, initial growth inhibition tests in 1.5% (w/v) NaCl showed no effect on pathogens. We found that digitiferin is secreted into mucus, where NaCl concentrations are lower than in seawater. Hence, we hypothesized that it is active against pathogens in low-salt environments. By re-evaluating under low-salt conditions, we discovered that digitiferin kills Vibrio species. Digitiferin homologs were found in multiple coral species, suggesting that digitiferin may serve as a first-line defense mechanism and determine disease susceptibility in corals. These findings enhance our understanding of coral-pathogen interactions and will facilitate the development of techniques to overcome Vibrio disease.