New findings on Tenacibaculum could be used for vaccine development

Iron plays a fundamental role in bacterial development and is a key factor in virulence. During infection, bacteria can absorb iron with the help of chelating molecules or siderophores.

Studies have shown, through functional biology experiments, that Tenacibaculum dicentrarchi has several systems to acquire iron; one that involves the synthesis of siderophores and another that uses haem groups as iron sources, writes Fish Farming Expert's Chilean sister site, Salmonexpert.cl.

Since these mechanisms may be inherent to T. dicentrarchi isolates, one strategy for vaccine design involves identifying proteins that might be involved in the pathogen-host interaction, specifically evoking an immune response in fish.

In a new published research, scientists from Andrés Bello University (UNAB), the Incar Centre, and the Molecular Epidemiology for Life of Science Research Institute, led by Dr Ruben Avendaño, characterised how iron limitation affects protein expression of T. dicentrarchi, with a primary focus on virulence factors and proteins associated with iron uptake.

Proteomic analysis, which was carried out using two strains of T. dicentrarchi (CECT 7612 T type strain and Chilean strain TdCh05) grown under normal (control) and iron-limited conditions, mimicking the host environment, revealed that some proteins are differentially expressed and others are not. This expression is associated with its biological role as could be evidenced in the article.

Mechanisms associated with iron uptake

For example, Avendaño explains that within the virulence factors they analysed the toxins and the gliding proteins, which allow the movement of the bacteria and facilitate its adhesion to surfaces. This group of proteins showed a greater diversity in expression between both growth conditions and between the type strain from European sea bass (type strain) and the Chilean strain from Atlantic salmon.

“Common proteins are upregulated and associated with gliding proteins such as GldH, GldL and SprE. It is interesting to note that collagenase A protein is downregulated. This protein is capable of breaking the peptide bonds of collagen, which is a component of fish skin. This result seems contradictory, however, even under iron deficiency conditions, the expression of genes associated with adhesion, biofilm formation and proteolytic activity of the type strain is negatively exacerbated. On the contrary, the proteins associated with iron uptake mechanisms found in both strains are all upregulated, which confirms that this component is very important in the fish infection process,” says the UNAB expert.

Regarding siderophores, both T. dicentrarchi strains responded to iron-limiting conditions and share the expression of proteins, especially those of the iron oxidation and reduction pathway.

“Among them, the TonB-dependent receptor and the iron-limiting resistance protein SufA stand out as the two most highly expressed proteins that are shared by both strains. Precisely, these two proteins have been described as relevant for iron uptake and the virulence of pathogens other than T. dicentrarchi, which suggests a relevant role when infection occurs in the fish,” the scientist states.

On the other hand, 14 metabolic proteins were downregulated, mainly associated with amino acid biosynthesis within the organophosphate metabolic process category. Furthermore, the isolates did not behave in the same way, which denotes the difference in virulence potential between the different T. dicentrarchi isolates.

Future vaccine

Regarding how these results could be used for a possible vaccine, Avendaño says that, in addition to deepening basic knowledge about the pathogen, the researchers have also been collaborating with different pharmaceutical companies in the search for a product that prevents or mitigates tenacibaculosis in salmon farming.

“We have results from a prototype vaccine for T. dicentrarchi evaluating precisely this iron uptake mechanism. Unfortunately, the results are not as spectacular as we thought and may be directly related to the existence of intra-specific diversity within this pathogen. However, our studies suggest that proteins associated with the iron uptake mechanism could be a target to reduce the infection potential of the bacteria. In this sense, it is worth remembering that pathogens do not have only one infection mechanism, therefore, a vaccine can reduce the symptoms associated with tenacibaculosis, but not eradicate it. All of this must go hand in hand with other operational measures,” concludes the researcher.

Read the study titled "Proteomic characterization of Tenacibaculum dicetrarchi under iron limitation reveals an upregulation of proteins related to iron oxidation and reduction metabolism, iron uptake systems and gliding motility", here.