A complementary LC-ESI-MS and MALDI-TOF approach for screening antibacterial proteomic signature of farmed European Sea bass mucus

• LC-ESI-MS analysis enables exploring AMP mucus proteome.
• We identify chrysophsin-like peptides from mucus of European Sea bass.
• Candida albicans and Aeromonas salmonicida are sensitive to Chrysophsins.
• Chrysophsins are secreted by immune cells and released in mucus.
• Chrysophsins are detected more efficiently than piscidins within European Sea bass mucus.

Antibacterial protection in the mucus is provided by antimicrobial compounds and till now few numbers of AMP and proteins were identified. Herein, mass spectral profiling of fresh mucus from farmed sea bass (Dicentrarchus labrax) using Matrix-assisted laser desorption/ionization-time-of-flight mass spectrometer (MALDI-TOF) and liquid chromatography mass spectrometry is investigated in order to survey the infective/healthy status of the mucus. We identify AMP peptides of 2891.7, 2919.45 and 2286.6 Da molecular weight respectively and characterize Chrysophsins in the mucus of Dicentrarchus labrax. These peptides display broad-spectrum bactericidal activity against Gram-negative (Minimum Inhibitory Concentrations namely MICs < 0.5 μM) and Gram-positive bacteria (MICs < 0.5 μM) including Escherichia coli and Bacillus subtilis. Furthermore, sensitivity to yeast Candida albicans is reported for the first time and shows interesting MICs of less than 2 μM. We also demonstrate that the fish pathogen Aeromonas salmonoicida is sensitive to Chrysophsins (MICs ranging between 5 and 14 μM). Our mucus molecular mass mapping developed approach allows for fast exploration of immune status. Our data provides evidence that Chrysophsins are secreted by immune cells and are released in mucus of non-challenged farmed European sea bass. These results suggest that Chrysophsins, secreted by gills of red sea bream, are an important widespread component of Teleostei defense against disease.