New knowledge and techniques are currently being sought to reduce mortality or to improve production rates of known or new farmed fish species. Gilthead seabream (Sparus aurata) is a widely consumed species in the Mediterranean and of great economic interest. In this context, the study of the function of antimicrobial peptides present in sea bream, such as hepcidins, and their involvement in the response to bacterial, fungal or viral infections may contribute to the improvement of the culture of this species.
In this study, we have located in the genome of seabream and compared the hamp2.0 and hamp2.15 genes and their respective mature peptides, Hamp2α and Hamp2Ω, by means of Clustal omega alignments. We found that both genes are type 2 hepcidins with high sequence and secondary structure similarity to each other and to other fish hepcidins. Furthermore, we have studied by qPCR their basal expression in healthy and Vibrio harveyi infected fish. Both were found to be differentially expressed at basal level (Figure 1A) and during Vibrio harveyi infection (Figure 1B).
The hamp2.0 gene showed higher basal expression values in liver, skin, gonad and spleen, and higher expression in head kidney, gut, spleen and skin in infected fish. Meanwhile, the hamp2.15 gene was predominantly expressed constitutively in brain, liver and gonad, with higher expression in skin, kidney and spleen. Furthermore, both peptides inhibited the in vitro growth of V. harveyi (an opportunistic pathogenic bacterium) while enhancing the growth of Shewanella putrefaciens SpPdp11 (a probiotic obtained from the skin of healthy seabream).
In conclusion, hamp2.0 and hamp2.15 are highly conserved in both sequence and function compared to fish hepcidins. Both are involved in the immune response, are expressed in tissues with immune function such as liver and spleen, and have the capacity to inhibit pathogenic bacteria such as V. harveyi. Curiously, the concentration of peptide in the in vitro assays was of little relevance. Furthermore, both peptides increase the growth of beneficial bacteria such as S. putrefaciens SpPdp11. More studies are needed to further investigate the function of these peptides in the immunity of seabream.
Acknowledgements
Jhon A. Serna-Duque has a PhD grant (FPU19/02192). This work has been financed by the project MCIN/ AEI /10.13039/501100011033 (grant number PID2020-113637RB-C21) and is part of the ThinkInAzul programme supported by MCIN with funding from European Union Next Generation EU (PRTR-C17.I1) and by the Comunidad Autónoma de la Región de Murcia-Fundación Séneca (Murcia, Spain).