Dietary Inclusion of Hydrolyzed Debaryomyces hansenii Yeasts Modulates Physiological Responses in Plasma and Immune Organs of Atlantic Salmon (Salmo salar) Parr Exposed to Acute Hypoxia Stress

Cyberlindnera jadinii yeast as a functional protein source: Modulation of immunoregulatory pathways in the intestinal proteome of zebrafish (Danio rerio)

Yeasts contain bioactive components that can enhance fish immune robustness and disease resistance. Our study focused on analyzing intestinal immunoregulatory pathways in zebrafish (Danio rerio) using iTRAQ and 2D LC-MS/MS to quantify intestinal proteins. Zebrafish were fed either control diet (C) or diet supplemented with autolyzed Cyberlindnera jadinii (ACJ). KEGG analysis revealed that ACJ yeast diet induced increased abundance of proteins related to arginine and proline metabolism, phagosome, C-lectin receptor signaling, ribosome and PPAR signaling pathways, which can modulate and enhance innate immune responses. ACJ yeast diet also showed decreased abundance of proteins associated with inflammatory pathways, including apoptosis, necroptosis and ferroptosis. These findings indicate boosted innate immune response and control of inflammation-related pathways in zebrafish intestine. Our findings in the well annotated proteome of zebrafish enabled a detailed investigation of intestinal responses and provide insight into health-beneficial effects of yeast species C. jadinii, which is relevant for aquaculture species.

Evidence that fish death after Vibrio vulnificus infection is due to an acute inflammatory response triggered by a toxin of the MARTX family

Vibrio vulnificus is an emerging zoonotic pathogen associated with fish farms that is capable of causing a hemorrhagic septicemia known as warm-water vibriosis. According to a recent transcriptomic and functional study, the death of fish due to vibriosis is more related to the inflammatory response of the host than to the tissue lesions caused by the pathogen. In this work, we hypothesize that the RtxA1 toxin (a V. vulnificus toxin of the MARTX (Multifunctional Autoprocessing Repeats in Toxin) family) is the key virulence factor that would directly or indirectly trigger this fatal inflammatory response. Our hypothesis was based on previous studies that showed that rtxA1-deficient mutants maintained their ability to colonize and invade, but were unable to kill fish. To demonstrate this hypothesis, we infected eels (model of fish vibriosis) by immersion with a mutant deficient in RtxA1 production and analyzed their transcriptome in blood, red blood cells and white blood cells during early vibriosis (0, 3 and 12 h post-infection). The transcriptomic results were compared with those obtained in the previous study in which eels were infected with the V. vulnificus parental strain, and were functionally validated. Overall, our results confirm that fish death after V. vulnificus infection is due to an acute, early and atypical inflammatory response triggered by RtxA1 in which red blood cells seem to play a central role. These results could be relevant to other vibriosis as the toxins of this family are widespread in the Vibrio genus.

Dietary Debaryomyces hansenii promotes skin and skin mucus defensive capacities in a marine fish model

The present study explores the effects of two supplementation levels of Debaryomyces hansenii (1.1% and 2.2%) as a probiotic in a reference low fish meal-based diet on the skin mucosal tissue in Sparus aurata. This study includes the evaluation of fish performance coupled with a holistic study of the skin mucosa: i) a transcriptomic study of the skin tissue, and ii) the evaluation of its secreted mucus both in terms of skin mucosal-associated biomarkers and its defensive capacity by means of co-culture analysis with two pathogenic bacteria. Results showed that after 70 days of diet administration, fish fed the diet supplemented with D. hansenii at 1.1% presented increased somatic growth and a better feed conversion ratio, compared to fish fed the control diet. In contrast, fish fed the diet including 2.2% of the probiotic presented intermediate values. Regarding gene regulation, the probiotic administration at 1.1% resulted in 712 differentially expressed genes (DEGs), among which 53.4% and 46.6% were up- and down-regulated, respectively. In particular, D. hansenii modulated some skin biological processes related to immunity and metabolism. Specifically, D. hansenii administration induced a strong modulation of some immune biological-related processes (61 DEGs), mainly involved in B- and T-cell regulatory pathways. Furthermore, dietary D. hansenii promoted the skin barrier function by the upregulation of anchoring junction genes (23 DEGs), which reinforces the physical defense against potential skin damage. In contrast, the skin showed modulated genes related to extracellular exosome and membrane organization (50 DEGs). This modulated functioning is of great interest, particularly in relation to the increased skin mucus defensive capacity observed in the bacterial co-culture in vitro trials, which could be related to the increased modulation and exudation of the innate immune components from the skin cells into the mucus. In summary, the modulation of innate immune parameters coupled with increased skin barrier function and cell trafficking potentiates the skin's physical barrier and mucus defensive capacity, while maintaining the skin mucosa's homeostatic immune and metabolic status. These findings confirmed the advantages of D. hansenii supplementation in low fish meal-based diets, demonstrating the probiotic benefits on cultured marine species.

Debaryomyces hansenii supplementation in low fish meal diets promotes growth, modulates microbiota and enhances intestinal condition in juvenile marine fish

BACKGROUND

The development of a sustainable business model with social acceptance, makes necessary to develop new strategies to guarantee the growth, health, and well-being of farmed animals. Debaryomyces hansenii is a yeast species that can be used as a probiotic in aquaculture due to its capacity to i) promote cell proliferation and differentiation, ii) have immunostimulatory effects, iii) modulate gut microbiota, and/or iv) enhance the digestive function. To provide inside into the effects of D. hansenii on juveniles of gilthead seabream (Sparus aurata) condition, we integrated the evaluation of the main key performance indicators coupled with the integrative analysis of the intestine condition, through histological and microbiota state, and its transcriptomic profiling.

RESULTS

After 70 days of a nutritional trial in which a diet with low levels of fishmeal (7%) was supplemented with 1.1% of D. hansenii (17.2 × 10⁵ CFU), an increase of ca. 12% in somatic growth was observed together with an improvement in feed conversion in fish fed a yeast-supplemented diet. In terms of intestinal condition, this probiotic modulated gut microbiota without affecting the intestine cell organization, whereas an increase in the staining intensity of mucins rich in carboxylated and weakly sulphated glycoconjugates coupled with changes in the affinity for certain lectins were noted in goblet cells. Changes in microbiota were characterized by the reduction in abundance of several groups of Proteobacteria, especially those characterized as opportunistic groups. The microarrays-based transcriptomic analysis found 232 differential expressed genes in the anterior-mid intestine of S. aurata, that were mostly related to metabolic, antioxidant, immune, and symbiotic processes.

CONCLUSIONS

Dietary administration of D. hansenii enhanced somatic growth and improved feed efficiency parameters, results that were coupled to an improvement of intestinal condition as histochemical and transcriptomic tools indicated. This probiotic yeast stimulated host-microbiota interactions without altering the intestinal cell organization nor generating dysbiosis, which demonstrated its safety as a feed additive. At the transcriptomic level, D. hansenii promoted metabolic pathways, mainly protein-related, sphingolipid, and thymidylate pathways, in addition to enhance antioxidant-related intestinal mechanisms, and to regulate sentinel immune processes, potentiating the defensive capacity meanwhile maintaining the homeostatic status of the intestine.

From a cell model to a fish trial: Immunomodulatory effects of heat-killed Lactiplantibacillus plantarum as a functional ingredient in aquafeeds for salmonids

Paraprobiotics (dead/inactivated probiotics) are promising candidates in functional feeds to promote growth performance, modulate intestinal microbiota and enhance immune response of fish. During industrial production, fish are exposed to several stressful conditions such as handling, sub-optimal nutrition and diseases that can lead to reduced growth, increased mortalities and large economical losses. Such problems can be mitigated by use of functional feeds, leading to more-sustainable aquaculture and improved animal welfare. Lactiplantibacillus plantarum strain L-137 is a common bacterium found in fermented Southeast Asian dish made from fish and rice. The benefits of its heat-killed form (HK L-137) related to growth performance and immunomodulation have been studied in farmed fish such as Nile Tilapia (Oreochromis niloticus), striped catfish (Pangasianodon hypophthalmus) and bighead catfish (Clarias macrocephalus). To study if such benefits can also be observed in salmonids, we worked both at in vitro level using an intestinal epithelium cell line from rainbow trout (Oncorhynchus mykiss; RTgutGC) stimulated with HK L-137 (Feed LP20™) and at in vivo level with pre-smolt Atlantic salmon (Salmo salar) fed HK L-137 at different inclusion levels (20, 100 and 500 mg of Feed LP20™ kg-1 feed). In RTgutGC, the results showed that the barrier function of the cell monolayer was strengthened along with an increased production of IL-1β and a decreased production of Anxa1, indicating a modulation of the immune response. Interestingly, a similar trend was detected at the in vivo level in distal intestine from fish fed the highest inclusion level of HK L-137. Here, a lower production of Anxa1 was also detected (after a 61-day feeding period) in addition to an increase of total plasma IgM in the same group. Furthermore, the RNA-seq analysis showed that HK L-137 was able to modulate the gene expression of pathways related to molecular function, biological process and cellular component in distal intestine, without compromising fish performance and gut microbiota. Taken together, our study has shown that HK L-137 can modulate physiological response of Atlantic salmon, making fish more robust against stressful conditions during production.

Probiotic Debaryomyces hansenii CBS 8339 yeast enhanced immune responses in mice

This study aimed to examine the effect of Debaryomyces hansenii CBS 8339 on innate immune responses in mice. Thirty BALB/c mice were randomly treated with phosphate buffered saline (PBS) (control) and two D. hansenii (Dh) doses: Dh 10ˆ6 CFU (colony forming units) and Dh 10ˆ8 CFU daily for 15 days. Spleen, blood, and gut samples were taken on days 7 and 15. Mouse splenocytes were isolated and challenged with Escherichia coli. Immunological assays and immune-related gene expressions were performed. Serum was obtained from blood for total IgA and IgG antibody titer determination. Gut samples were taken for yeast colonization assessment. Phagocytosis, respiratory burst activity, and nitric oxide production in mice were mainly enhanced (p < 0.05) upon 7 days of D. hansenii intake at a concentration of 10ˆ8 CFU before and after bacterial challenge. Moreover, oral D. hansenii in mice upregulated (p < 0.05) gene expression of pro-inflammatory cytokines (INF-γ, IL-6 and IL-1β) before or after E. coli challenge on day 7 but downregulated (p < 0.05) on day 15. Furthermore, total serum IgG and IgA titers were higher (p < 0.05) in Dh 10ˆ8 CFU at days 7 and 15, and only at day 7, respectively, than that in the other dose and control groups. Finally, D. hansenii was detected in the gut of mice that received the treatments, suggesting that yeast survived gastrointestinal transit. Altogether, a short period (7 days) of D. hansenii CBS 8339 oral delivery improved immune innate response on mice.

Immune Modulation Ability of Hepcidin from Teleost Fish

Simple Summary

Antimicrobial peptides are part of the fish defense system, which can directly eliminate pathogenic microorganisms and, at the same time, regulate the immune response against them. This study evaluated the immunomodulatory effects of the antimicrobial peptide hepcidin in both juvenile fish and fish leukocyte cells. The results showed that hepcidin increased the expression of TNF-α, IL-1β, and IL-10 cytokines in leukocyte cells from trout. Moreover, the mRNA expressions of the same cytokines were up-regulated in different immune tissue of sea bass, confirming in vitro results. This study provides new insights into immunomodulatory function complementary to hepcidin’s previously established antimicrobial activity modulating the pro- and anti-inflammatory responses in teleost fish.

Abstract

Antimicrobial peptides (AMP) play an essential role in the innate immune system, modulating the defense response. In a previous study, we demonstrated the antimicrobial activity of synthetic hepcidin (hep20) from rainbow trout (Oncorhynchus mykiss), and its protective effect in European sea bass (Dicentrarchus labrax) challenged with Vibrio anguillarum. Additionally, we described the uptake and distribution of hep20 in different tissues and leukocyte cells. Interestingly, various AMPs characterized in high vertebrates, called host defense peptides (HDPs), also possess immunomodulation activity. For that reason, the present study explores the immunomodulatory abilities of hep20 through in vitro and in vivo studies. First, a monocyte/macrophage RTS-11 cell line from rainbow trout was used to evaluate hep20 effects on pro- and anti-inflammatory cytokines in fish leukocyte cells. Next, the European sea bass juveniles were used to determine if hep20 can regulate the expression of cytokines in fish immune tissues. The results show that hep20 was uptake inner to RTS-11 cells and was able to induce the expression of IL-10, IL-1β, and TNFα at transcriptional and protein levels. Then, the European sea bass juveniles were given intraperitoneal injections of the peptide. At 1, 3, 7, 14, and 21 days post-injection (dpi), IL-10, IL -1β, and TNFα mRNA were quantified in the anterior gut, spleen, and head kidney. The hep20 was able to up-regulate cytokine gene expression in these tissues, mainly in the head kidney. Furthermore, the evaluated cytokines showed a cyclical tendency of higher to lesser expression. Finally, a bioinformatics analysis showed that the structure adopted by hep20 is similar to the γ-core domain described for cysteine-stabilized AMP, defined as immunomodulatory and antimicrobial, which could explain the ability of hep20 to regulate the cytokine expression. This study provides new insights into immunomodulatory function complementary to the previously established antimicrobial activity of hep20, suggesting a role as an HDP in teleost fish. These facts are likely to be associated with molecular functions underpinning the protective effect of fish hepcidin against pathogens.