Proteomic profile of the skin mucus of farmed gilthead seabream (Sparus aurata).

Unlabelled: Fish skin mucus is the first line of defense against infections and it discriminates between pathogenic and commensal bacterial strains. Mucus composition varies amongst fish species and is influenced by endogenous and exogenous factors. This study describes the first proteome map of the epidermal mucus of farmed gilthead seabream (Sparus aurata). We used an integrative proteomic approach by combining a label-free procedure (LC-MS/MS) with the classical 2-DE-PMF-MS/MS methodology. The identified mucosal proteins were clustered in four groups according to their biological functions. Structural proteins (actins, keratins, tubulins, tropomyosin, cofilin-2 and filamin-A) and metabolic proteins (ribosomal proteins, proteasomal subunits, NACA, VCP, histones, NDPK, transferrin, glycolytic enzymes, ATP synthase components, beta-globin, Apo-A1 and FABP7) were the best represented functional categories. We also found proteins involved in stress response (WAP65, HSPC70, Cu,Zn-SOD, and PRDX1 and PRDX2) and signal transduction (PP2A 65kDa regulatory subunit, 14-3-3 protein beta/alpha, tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein, RhoGDI and PEBP1). Most of the identified proteins address different aspects of the innate immune response. Additionally, we analyzed bacterial peptides identified in the skin mucus of healthy S. aurata. These results revealed that genera belonging to the Lactobacillales order constitute the most abundant microorganism populations in this habitat.

Biological Significance: This work shows that proteomic methods can be used to characterize fish skin mucus. Using a coupled approach of LC-MS/MS and a 2-DE-PMF-MS/MS, we have obtained the first comprehensive view of the skin mucosal proteome of S. aurata, a fish species that is economically relevant for Mediterranean aquaculture. We identified a panel of proteins involved in a variety of biological functions, particularly in the innate immune response. Furthermore, to our knowledge, this is the first time a proteomic approach has been used to examine the microbiota in the skin mucus of a fish species. Overall, these results support further immunological researches in S. aurata and are relevant for the culture of this important fish species.