Intermediary metabolic response and gene transcription modulation on the Sub-Antarctic notothenioid Eleginops maclovinus (Valenciennes, 1930) injected with two strains of Piscirickettsia salmonis

Discovery of BbX transcription factor in the patagonian blennie: Exploring expression changes following combined bacterial and thermal stress exposure

High-Mobility Group (HMG) proteins are involved in different processes such as transcription, replication, DNA repair, and immune response. The role of HMG proteins in the immune response of fish has been studied mainly for HMGB1, where its expression can be induced by the stimulation of viral/bacterial PAMPs and can act as a proinflammatory mediator and as a global regulator of transcription in response to temperature. However, for BbX this role remains to be discovered. In this work, we identified the BbX of E. maclovinus and evaluated the temporal expression levels after simultaneous challenge with P. salmonis and thermal stress. Phylogenetic analysis does not significantly deviate from the expected organismal relationships suggesting orthologous relationships and that BbX was present in the common ancestor of the group. BbX mRNA expression levels were very high in the intestinal tissue of E. maclovinus (foregut, midgut, and hindgut). Nevertheless, the protein levels analyzed by WB showed the highest levels of BbX protein in the liver (constitutive expression). On the other hand, the mRNA expression levels of BbX in the liver of E. maclovinus injected with P. salmonis and subjected to thermal stress showed an increase at days 16 and 20 in all treatments applied at 12 °C and 18 °C. Meanwhile, the protein levels quantified by WB showed a statistically significant increase in the HMG-Bbx at all experimental times (4, 8, 12, 16, and 20 dpi). However, at 4 dpi the HMG-Bbx protein levels were much higher than the other days evaluated. The results suggest that BbX protein may be implicated in the response mechanism to temperature and bacterial stimulation in the foregut, midgut, hindgut, and liver, according to our findings at the level of mRNA and protein. Furthermore, our WB analysis suggests an effect of P. salmonis on the expression of this protein that can be observed in condition C+ 12 °C compared to C- 12 °C. Then, there is an effect of temperature that can be evidenced in the condition AM 18 °C and SM 18 °C, compared to AB 18 °C and SB 18 °C at 4, 8, and 12 dpi. We found not differences in the levels of this protein if the thermal stress is achieved through acclimatization or shock. More research is necessary to clarify the importance of this type of HMG in the immune response and thermal tolerance in fish.

Transcriptional modulation of immune genes in gut of Sub-Antarctic notothenioid fish Eleginops maclovinus challenged with Francisella noatunensis subsp. noatunensis

The search for functional foods that improve the immune response has traditionally been focused on lymphoid tissue and the intestinal mucosa. However, it is unknown whether there is a different immune response in different portions of the gut following exposure to a bacterial pathogen. We challenged Eleginops maclovinus intraperitoneally (i.p) with Francisella noatunensis subsp. noatunensis and measured mRNA transcripts related to innate and adaptive immune responses in different parts of the gut (foregut, midgut and hindgut). We used control (i.p only with bacterial culture medium), low dose (i.p of F. noatunensis at 1 × 10¹ bact/μL), medium dose (i.p of F. noatunensis at 1 × 10⁵ bact/μL) and high dose (i.p of F. noatunensis at 1 × 10¹⁰ bact/μL) groups in our experiments. We sampled fish at days 1, 3, 7, 14, 21, and 28 post-injection. We observed tissue-specific expression of TLR1, TLR5, TLR8, MHCI, MHCII and IgM, and transcription of these immune markers was lower in foregut and higher in midgut and hindgut. We detected Francisella genetic material (DNA) in fish stimulated with a high dose from day 1-28 in foregut, midgut, and hindgut. However, we could only detect Francisella DNA in fish stimulated the medium and low dose at later timepoints in the foregut (21-28 days post injection "dpi") and hindgut (low dose from day 7-28 dpi). Our results suggest that the immune responses to bacterial pathogens occur throughout the gut, but certain segments may be more susceptible to infection because of their cellular morphology (anterior, middle and posterior).

Antimicrobial resistance in Chilean marine-farmed salmon: Improving food safety through One Health

Aquaculture is seen as an essential requirement for improving food security and nutrition. Fish such as salmonids are a primary source of protein and essential nutrients. Aquaculture provide income for communities across the world and have a smaller carbon footprint than terrestrial animal-production systems. However, fish diseases are a constant threat, and the use of antibiotics is a source of concern due to its adverse impacts on the environment and human health. Chilean salmon farming has made several efforts to reduce the use of antibiotics for the eradication of piscirickettsiosis, a disease caused by the gram-negative bacteria Piscirickettsia salmonis. Excessive amounts of antibiotics continue to be used in Chilean aquaculture, playing an important role in the emerging public health crisis of antimicrobial resistance. Without doubt, P. salmonis is becoming increasingly resistant to important frontline antimicrobial classes, with severe implications for the future treatment of infectious human and animal diseases. Antimicrobial-resistant bacteria as well as antibiotic residues from salmon production are spreading in the environment, and thus both salmon food commodities and wild organisms can become a source of resistant bacteria that can be transmitted to humans as foodborne contaminants. This urgent threat needs to be addressed by implementing national strategies in compliance with international standards that include both prudent antimicrobial use in marine salmon farms and the investment towards a One Health approach, which combines human, animal and environmental health.