Researchers from the Department of Biochemistry and Molecular Biology of the University of Córdoba, in collaboration with the University of Murcia, have identified for the first time the set of proteins present in the mucus of sea bream skin. The study shows that these biomolecules are involved in the immune response of the fish, so their identification is the first step in preventing bacterial infections during their culture. These diseases, scientists indicate, are one of the main scourges that affect the aquaculture sector, causing large economic losses.
Protein analysis has also allowed experts to identify a series of microorganisms of bacterial origin that are part of the skin's microbiota and that, like the intestinal flora, live naturally in the epidermis of sea bream. Until now, according to the experts, little data was known on the composition of this microflora, so their analysis would provide new information about its role in the defense of the organism against pathogens.
Researchers have characterized a total of 52 proteins present in the mucus of sea bream skin, a layer that surrounds the epidermis and acts as a protective barrier between the body and the environment in which it grows. This mucous covering, present in all fish, is semi-permeable in a way that allows the exchange of substances (nutrients, water, gases, hormones, gametes ...) between the skin and the environment.
The structure of the mucosa varies depending on endogenous and exogenous factors. The former are related to parameters such as age or sex. On the other hand, the external ones refer to aspects such as nutrition, the quality of the environment or the state of health of the fish. "Based on these conditioning factors, the protein composition of mucus differs, both in variety and quantity. In our case, we have elaborated the first proteomic profile of the mucus of the healthy gilthead seabream from aquaculture, that is, we have defined the set of proteins present in this structure in a given circumstance such as the good general state of health of the animal ”, he explains to the Discover Foundation, the main researcher of this project, María José Prieto-Álamo, from the University of Córdoba.
Of the proteins identified, most of them are related to the body's immune response to foreign substances and agents. For experts, this characteristic reinforces the role of the mucosa as the first defense barrier against diseases.
In this way, the researcher points out that the mucosa proteome of healthy sea bream acts as a kind of reference marker, since any change in its composition will, in turn, indicate a modification of the factors that affect it. “If a gilthead sea bream is sick, the proteins in the mucus on its skin will be different from those in healthy fish. Therefore, variations in the proteomic profile will be an indicator that something is changing in the fish ”, he asserts.
From these modifications, experts could deduce, for example, if the gilthead seabream is going to suffer or is suffering from some bacterial disease during its cultivation. “This type of infection is common in aquaculture, seriously affecting the sector. If we identify the proteins that vary their expression in the diseased mucosa in time, we will be able to prevent the pathology and avoid economic losses in the cultivation of sea bream, an industry that, due to production volume and commercial value, ranks first in Andalusia ”, indicates Prieto-Álamo.
Commensal bacteria
During the analysis of the mucosa, whose complete profile is collected in the article 'Proteomic profile of the skin mucus of farmed gilthead seabream ( Sparus aurata )', published in the Journal of Proteomics , the researchers discovered another series of proteins that did not fit with the proteomic profile of gilthead seabream but had a bacterial origin. “By working with healthy fish, we ruled out that they were pathogenic microorganisms. So it was evident that it was bacteria that were part of the microbiota of the gilthead sea bream skin, little known ”, the scientist clarifies.
The microbiota is made up of a wide variety of bacterial species that protect against colonization by other pathogenic microorganisms. This microbial flora is present in the intestine, mucous membranes, skin and other tissues, both of animals and humans.
In the case of the microbiota of the epidermis of seabream, the researchers point out that it is made up of commensal bacteria, that is, they provide the host organism, the fish, one benefit in exchange for another. “It is a mutual use that is known as commensal symbiosis. The bacterium finds a protected habitat rich in nutrients and the gilthead sea bream is protected against opportunistic pathogens that would take the place of the bacterium if it were not present ”, the expert specifies.
This competition between bacteria that grow naturally on the skin and pathogenic microorganisms is called microbial antagonism, a defense mechanism to protect the animal from foreign agents. “The specific function of the golden skin mucus microbiota is unknown. We only know that it is made up of commensal bacteria but this study is a first step to delve into its protective and preventive role against diseases ”, indicates the person in charge of this project, financed by the Ministry of Economy and Competitiveness.
In their next work, the experts will analyze the changes that occur in the composition of the microbiota and the proteome in the face of different pathophysiological variables.
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