Dietary administration of the probiotic SpPdp11: Effects on the intestinal microbiota and immune-related gene expression of farmed Solea senegalensis treated with oxytetracycline

Evaluation of the Differential Postbiotic Potential of Shewanella putrefaciens Pdp11 Cultured in Several Growing Conditions

The increased knowledge of functional foods has led to the development of a new generation of health products, including those containing probiotics and products derived from them. Shewanella putrefaciens Pdp11 (SpPdp11) is a strain described as a probiotic that exerts important beneficial effects on several farmed fish. However, the use of live probiotic cells in aquaculture has limitations such as uncertain survival and shelf life, which can limit their efficacy. In addition, its efficacy can vary across species and hosts. When probiotics are administered orally, their activity can be affected by the environment present in the host and by interactions with the intestinal microbiota. Furthermore, live cells can also produce undesired substances that may negatively impact the host as well as the risk of potential virulence reversion acquired such as antibiotic resistance. Therefore, new alternatives emerged such as postbiotics. Currently, there is no knowledge about the postbiotic potential of SpPdp11 in the aquaculture industry. Postbiotic refers to the use of bacterial metabolites, including extracellular products (ECPs), to improve host physiology. However, the production of postbiotic metabolites can be affected by various factors such as cultivation conditions, which can affect bacterial metabolism. Thus, the objective of this study was to evaluate the postbiotic potential of ECPs from SpPdp11 under different cultivation conditions, including culture media, temperature, growth phase, and salinity. We analyzed their hydrolytic, antibacterial, antiviral, and cytotoxic capacity on several fish cell lines. The results obtained have demonstrated how each ECP condition can exert a different hydrolytic profile, reduce the biofilm formation by bacterial pathogens relevant to fish, lower the titer of nervous necrosis virus (NNV), and exert a cytotoxic effect on different fish cell lines. In conclusion, the ECPs obtained from SpPdp11 have different capacities depending on the cultivation conditions used. These conditions must be considered in order to recover the maximum number of beneficial capacities or to choose the appropriate conditions for specific activities.

Dietary β-Glucan Alleviates Antibiotic-Associated Side Effects by Increasing the Levels of Antioxidant Enzyme Activities and Modifying Intestinal Microbiota in Pacific White Shrimp (Litopenaeus vannamei)

Antibiotics and their secondary metabolites are commonly found in aquatic ecosystems, leading to the passive exposure of many aquatic animals to low doses of antibiotics, which can affect their health. However, there is limited information available on how to mitigate the side effects of antibiotics on normal aquatic animals. This study aimed to investigate the potential of dietary β-glucan to alleviate the side effects induced by antibiotics in Pacific white shrimp (Litopenaeus vannamei) (0.37 ± 0.02 g). A six-week feeding trial was conducted with four dietary treatments including a control, 1 g/kg β-glucan (β-glucan), 50 mg/kg oxytetracycline (OTC), and a combination of 50 mg/kg OTC and 1 g/kg β-glucan (Mix) groups. At the end of the trial, the growth performance, intestinal microbial composition, antioxidant capacity, and immune response of the shrimp were assessed. There were no significant differences in growth performance among the groups, but the condition factor of the shrimp in the Mix group was significantly decreased when compared to the control and β-glucan groups. The activities of hepatopancreas catalase (CAT) and serum phenol oxidase in the OTC group were significantly lower than those in the control group. On the other hand, the activities of hepatopancreas superoxide dismutase and CAT enzymes in the β-glucan group were significantly higher than those in the OTC group. The supplementation of β-glucan in combination with antibiotics significantly increased the CAT activity and bacteriolytic activity compared to the OTC and control groups, respectively. Moreover, an analysis of the intestinal microbiota revealed that the Observed_species estimator in the Mix group was significantly higher than that in the control group. Dietary antibiotics significantly increased the abundance of Actinobacteria at the phylum level, but the Mix group showed no significant difference. The supplementation of β-glucan in combination with antibiotics also significantly increased the relative abundance of Meridianimaribacter compared to the control group. Additionally, the synergistic influence of β-glucan with antibiotics increased the beta diversity of intestinal microbiotas. These findings suggest that the supplementation of β-glucan in combination with antibiotics on Pacific white shrimp can alleviate the low antioxidant capacity and immune response caused by antibiotics while enhancing the intestinal microbial composition. This provides a potential solution to mitigate the negative impacts of antibiotics in aquaculture.

Impact of different levels of handling on Solea senegalensis culture: effects on growth and molecular markers of stress

Aquaculture routine practices may cause stress induction on the fish and compromise their welfare affecting the production. This experiment aimed to evaluate the potential links between handling during culture with stress responses and growth on Senegalese sole (Solea senegalensis). We worked with two fish cohorts in terms of initial body weight and culture stage: Trial 1 included specimens in the fattening stage (226 ± 4.96 g) and Trial 2 animals in the pre-fattening stage (27.20 ± 0.44 g). The tested culture protocol, which lasted 6 and 4 months for Trial 1 and 2, respectively, mainly reduced handling-derived stressors in the experimental tanks via lowering routine samplings to a minimum. This decrease of the handling-derived stress was reflected in both trials with lower concentration of circulating cortisol in blood plasma from the experimental fish when compared to controls. Moreover, the proposed protocol promoted higher growth in the fish cultured in the less disturbing protocol in Trial 2. Higher specific growth rates and mean body weight and length were reported. In order to further explore the potential beneficial effects of our protocol, we studied the musculoskeletal from Trial 2 gene expression of key genes regulating glucocorticoid signaling pathway and apoptosis: glucocorticoid receptors 1 and 2 (gr1, gr2), heat shock protein 90 AA (hsp90aa), and caspase 6 (casp6). In line with the cortisol reduced level in this trial, gr1, hsp90aa, and casp6 genes showed lower expression in the samples coming from the experimental group. The findings of this study provide valuable information to the aquaculture industry for the management of Solea senegalensis stress and welfare.

Naturally occurring beneficial bacteria Vibrio alginolyticus X-2 protects seaweed from bleaching disease

Microbiome manipulation is gaining fresh attention as a way to mitigate diseases in aquaculture. The commercially farmed seaweed Saccharina japonica suffers from a bacterial-induced bleaching disease, which has major implications for the reliable supply of healthy sporelings. Here, we identify a beneficial bacterium, Vibrio alginolyticus X-2 that significantly reduces the risk of bleaching disease. By combining infection assays and multi-omic analyses, we provide evidence to suggest that the underlying protective mechanisms of V. alginolyticus X-2 involve maintaining epibacterial communities, increasing the gene expression of S. japonica related to immune and stress protection pathways, and stimulating betaine concentrations in S. japonica holobionts. Thus, V. alginolyticus X-2 can elicit a suite of microbial and host responses to mitigate the bleaching disease. Our study provides insights into disease control in farmed S. japonica through the application of beneficial bacteria. IMPORTANCE Beneficial bacteria can elicit a suite of microbial and host responses to enhance the resistance to bleaching disease.

Antibiotic application may raise the potential of methylmercury accumulation in fish

Mercury (Hg) biotransformation can significantly affect the Hg speciation and bioaccumulation in fish, where gut microbiota play an important role in this process. Antibiotics have been extensively used in aquaculture and can affect gut microbial structure. However, the influence of antibiotics on Hg biotransformation in fish has not been thoroughly understood. The present study investigated the effects of antibiotic (florfenicol) application on gut microbiota and subsequent impacts on Hg biotransformation and bioaccumulation in tilapia (Oreochromis mossambicus). The results showed that the florfenicol treatment did not affect IHg accumulation in the IHg-exposed fish or the MeHg accumulation in the MeHg-exposed fish. However, methylation was significantly weakened (from 0.015% d^-1 to 0.005% d^-1) and demethylation was completely terminated (from 0.046% d^-1 to non-observable level) in the florfenicol-treated fish as compared to the control fish. This can be ascribed to the major shift in the richness of microbial methylators/demethylators in fish gut. Furthermore, florfenicol disturbed the homeostasis of gut microbiome and enhanced the growth of opportunistic pathogens. Our results strongly suggested that antibiotic application significantly altered the gut microbial community, thereby increasing the potential of MeHg accumulation by fish. This study highlights the importance of appropriate use of antibiotics in aquaculture as well as decreasing the environmental risks of Hg contamination in fish.

Atlantic Salmon (Salmo salar) bacterial and viral innate immune responses are not impaired by florfenicol or tetracycline administration

Antibiotics are used to treat bacterial infections in fish aquaculture, and these drugs can interact with immune cells/the immune system and potentially leave fish vulnerable to viral, fungal, parasitic, or other bacterial infections. However, the effects of antibiotics on fish immunity have largely been overlooked by the aquaculture industry. We tested, at 12 and 20 °C, whether tetracycline and florfenicol (the most commonly used antibiotics in commercial aquaculture), affected the Atlantic salmon's capacity to respond to bacterial or viral stimulation. Atlantic salmon were acclimated to 12 or 20 °C and fed with tetracycline or florfenicol (100 and 10 mg kg of body weight^-1 day^-1, respectively) medicated feed for 15 or 10 days, respectively. Thereafter, we evaluated their immune function prior to, and after, an intraperitoneal injection of Forte Micro (containing inactivated cultures of Aeromonas salmonicida, Vibrio anguillarum, Vibrio ordalii and Vibrio salmonicida) or the viral mimic polyriboinosinic polyribocytidylic acid (pIC). We measured the transcript expression levels of 8 anti-bacterial and 8 anti-viral putative biomarker genes, and the innate (leukocyte respiratory burst, plasma lysozyme activity and hemolytic activity of the alternative complement pathway) and cellular (relative number of erythrocytes, lymphocytes and thrombocytes, and granulocytes such as monocytes and neutrophils) responses to these challenges. Overall, we only found a few minor effects of either tetracycline or florfenicol on immune gene expression or function at either temperature. Although several studies have reported that antibiotics may negatively affect fish immune responses, our results show that industry-relevant dietary tetracycline and florfenicol treatments do not substantially impact the salmon's innate immune responses. Currently, this is the most comprehensive study on the effects of antibiotics administrated according to industry protocols on immune function in Atlantic salmon.

Dietary therapeutic dose of oxytetracycline negatively influences the antioxidant capacity and immune-related genes expression in Nile tilapia Oreochromis niloticus (L.)

Effects of the dietary therapeutic dose of oxytetracycline (OTC) at 80 mg/kg biomass/day for consecutive 10 days on the behaviour, feed intake, mortality, residue accumulation and depletion, antioxidant capacity and immune-related genes expression in juvenile Nile tilapia Oreochromis niloticus were evaluated. OTC-dosing caused mortalities, reduced feed intake, and biomass reduction at 24.5-28.5 °C. OTC residues recorded on day 10 (161.40 ± 11.10 ng/g) were within the maximum residue limits of the Codex Alimentarius. The withdrawal period was 7 days as per the European Commission's regulation. Traces of residues were present even on day 42 post-OTC-dosing. Dietary OTC reduced the antioxidant capacity of the liver and muscle tissues and down-regulated the expression of tumour necrosis factor-α, interleukin-1β, and heat shock protein-70 genes in the liver significantly during the dosing period. The data generated on the biosafety of OTC-dosing may offer inputs for the development of management strategies in maintaining fish health and food safety.

Microbiota composition and intestinal integrity remain unaltered after the inclusion of hydrolysed Nannochloropsis gaditana in Sparus aurata diet

The use of lysed microalgae in the diet of carnivorous fish can increase the bioavailability of proteins and bioactive compounds, such as unsaturated fatty acids or vitamins in the digestive tract. These are essential molecules for the proper physiological development of fish in aquaculture. However, some antinutritional components and other undesirable molecules can be released from an excess of microalgae supplied, compromising the integrity of the intestine. The inclusion of small amounts of hydrolized microalgae in the fish diet can be a good strategy to avoid negative effects, improving the availability of beneficial compounds. Nannochloropsis gaditana is an interesting microalgae as it contains nutraceuticals. Previous studies reported beneficial effects after its inclusion in the diet of Sparus aurata, a widely cultured species in Europe and in all Mediterranean countries. However, administration of raw microalgae can produce intestinal inflammation, increased intestinal permeability, bacterial translocation and disturbance of digestion and absorption processes. The aim of this study was to evaluate changes in the intestinal microbiota and barrier stability of S. aurata fed with low inclusion (5%) hydrolysed N. gaditana. Intestinal microbiota was analyzed using Illumina MiSeq technology and libraries were constructed using variable regions V3–V4 of 16S rDNA molecules. Analysis were based in the identification, quantification and comparison of sequences. The predictive intestinal microbial functionality was analyzed with PICRUSt software. The results determined that the intestinal microbiota bacterial composition and the predictive intestinal microbiota functionality did not change statistically after the inclusion of N. gaditana on the diet. The study of gene expression showed that genes involved in intestinal permeability and integrity were not altered in fish treated with the experimental diet. The potential functionality and bacterial taxonomic composition of the intestinal microbiota, and the expression of integrity and permeability genes in the intestine of the carnivorous fish S. aurata were not affected by the inclusion of hydrolysed 5% N. gaditana microalgae.

A Tentative Study of the Effects of Heat-Inactivation of the Probiotic Strain Shewanella putrefaciens Ppd11 on Senegalese Sole (Solea senegalensis) Intestinal Microbiota and Immune Response

Concerns about safety, applicability and functionality associated with live probiotic cells have led to consideration of the use of non-viable microorganisms, known as paraprobiotics. The present study evaluated the effects of dietary administration of heat-inactivated cells of the probiotic strain Shewanella putrefaciens Ppd11 on the intestinal microbiota and immune gene transcription in Solea senegalensis. Results obtained were evaluated and compared to those described after feeding with viable Pdp11 cells. S. senegalensis specimens were fed with basal (control) diet or supplemented with live or heat inactivated (60 °C, 1 h) probiotics diets for 45 days. Growth improvement was observed in the group receiving live probiotics compared to the control group, but not after feeding with a probiotic heat-inactivated diet. Regarding immune gene transcription, no changes were observed for tnfα, il-6, lys-c1, c7, hsp70, and hsp90aa in the intestinal samples based on the diet. On the contrary, hsp90ab, gp96, cd4, cd8, il-1β, and c3 transcription were modulated after probiotic supplementation, though no differences between viable and heat-inactivated probiotic supplemented diets were observed. Modulation of intestinal microbiota showed remarkable differences based on the viability of the probiotics. Thus, higher diversity in fish fed with live probiotic cells, jointly with increased Mycoplasmataceae and Spirochaetaceae to the detriment of Brevinemataceae, was detected. However, microbiota of fish receiving heat-inactivated probiotic cells showed decreased Mycoplasmataceae and increased Brevinemataceae and Vibrio genus abundance. In short, the results obtained indicate that the viable state of Pdp11 probiotic cells affects growth performance and modulation of S. senegalensis intestinal microbiota. On the contrary, minor changes were detected in the intestinal immune response, being similar for fish receiving both, viable and inactivated probiotic cell supplemented diets, when compared to the control diet.

Rutin-added diet protects silver catfish liver against oxytetracycline-induced oxidative stress and apoptosis

It is unknown whether the flavonoid rutin can protect the silver catfish liver in response to exposure to a known stressor, such as the prophylactic usage of the antimicrobial agent oxytetracycline. Thus, the current study aimed to assess the effect of rutin incorporation into the silver catfish diet formulation on oxytetracycline-induced liver oxidative stress and apoptosis. Fish were split into four groups as follows: control, rutin (1.5 g kg diet^-1), oxytetracycline (0.1 g kg diet^-1) and rutin+oxytetracycline (1.5 g kg diet^-1 and 0.1 g kg diet^-1, respectively). After two weeks of feeding with the different diets (standard, rutin-, oxytetracycline and rutin+oxytetracycline-added diets), fish were euthanized to collect the liver. Although the rutin-added diet was unable to recover glutathione peroxidase activity, ascorbic acid and reduced glutathione (GSH) levels, which were depleted due to oxytetracycline consumption, it markedly diminished the oxidized glutathione (GSSG) content, thus decreasing the GSSG to GSH ratio, an important index of oxidative stress. It also increased glutathione reductase and markedly augmented glucose-6-phosphate dehydrogenase activities, which were declined after oxytetracycline ingestion. Furthermore, the rutin-added diet reestablished superoxide dismutase and catalase activities and reduced lipid peroxidation, nitric oxide and superoxide anion levels as well, all changes resulting from oxytetracycline consumption. Finally, it also prevented oxytetracycline-induced apoptosis through increasing heat shock protein 70 and markedly decreasing high mobility group box 1 and, consequently, reducing cleaved caspase-3 protein levels. Therefore, in conclusion, the incorporation of this flavonoid to the silver catfish diet protected the liver against oxytetracycline-induced liver oxidative stress and apoptosis.

Probiotic Shewanella putrefaciens (SpPdp11) as a Fish Health Modulator: A Review

Aquaculture is considered one of the largest food production sectors in the world. Probiotics have long been considered as a beneficial tool in this industry since these microorganisms improve the welfare of different fish species by modulating several physiological functions, such as metabolism, digestion, immune response, stress tolerance, and disease resistance, among others. SpPdp11, a probiotic isolated from the skin of healthy gilthead seabream, has been the center of attention in a good number of studies since its discovery. The purpose of this paper is to summarize, comment, and discuss the current knowledge related to the effects of SpPdp11 in two commercially important fish species in aquaculture (gilthead seabream and Senegalese sole). Furthermore, some considerations for future studies are also indicated.

Effects of Probiotics BaSC06 on Intestinal Digestion and Absorption, Antioxidant Capacity, Microbiota Composition, and Macrophage Polarization in Pigs for Fattening

This study aimed to compare the effects of BaSC06 and antibiotics on growth, digestive functions, antioxidant capacity, macrophage polarization, and intestinal microbiota of pigs for fattening. A total of 117 pigs for fattening with similar weight and genetic basis were divided into 3 groups: Anti group (containing 40 g/t Kitasamycin in the diet), Anti+Ba group (containing 20 g/t Kitasamycin and 0.5 × 108 CFU/kg BaSC06 in the diet) and Ba group (containing 1 × 108 cfu/Kg BaSC06 in the diet without any antibiotics). Each treatment was performed in three replicates with 13 pigs per replicate. Results showed that BaSC06 replacement significantly improved the ADG (P < 0.05), intestinal digestion and absorption function by increasing the activity of intestinal digestive enzymes and the expression of glucose transporters SGLT1 (P < 0.05) and small peptide transporters PEPT1 (P < 0.05). Besides, BaSC06 supplementation enhanced intestinal and body antioxidant capacity by activating the Nrf2/Keap1 antioxidant signaling pathway due to the increased expression of p-Nrf2 (P < 0.05). Notably, BaSC06 alleviated intestinal inflammation by inhibiting the production of pro-inflammatory cytokines, IL-8, IL-6, and MCP1 (P < 0.05), and simultaneously increasing the expression of M1 macrophage marker protein iNOS (P < 0.05) and M2 macrophage marker protein Arg (P < 0.05) in the intestinal mucosa. Moreover, BaSC06 promoted the polarization of macrophages to M2 phenotype by stimulating the STAT3 signaling pathway. It was also noted that BaSC06 improved microbiota composition by enhancing the proportion of Firmicutes, and reducing that of Bacteroidetes and Proteobacteria. Taken together, our results indicate that dietary supplementation of BaSC06 in pigs for fattening improves the growth, mucosal structure, antioxidative capacity, immune functions (including increasing M1 and M2 polarization of macrophage) and composition of intestinal microbiota, which is much better than antibiotics, suggesting that it is an effective alternative to antibiotics in the preparation of pig feed.

Dietary administration of the probiotic Shewanella putrefaciens to experimentally wounded gilthead seabream (Sparus aurata L.) facilitates the skin wound healing

The effect of the probiotic Shewanella putrefaciens Pdp11 (SpPdp11) was studied on the skin healing of experimentally wounded gilthead seabream (Sparus aurata L.). Two replicates (n = 12) of fish were fed CON diet or SP diet for 30 days. Half of the fish were sampled while the others were injured and sampled 7 days post-wounding. Results by image analysis of wound areas showed that SpPdp11 inclusion facilitated wound closure. Compared with the CON group, fish in SP group sampled 7 days post-wounding had a significantly decreased serum AST and increased ALB/GLOB ratio. Furthermore, protease and peroxidase activities were significantly increased in skin mucus from fish in SP group sampled 7 days post-wounding, compared with those fed CON diet. Additionally, SP diet up-regulated the gene expression of antioxidant enzymes, anti-inflammatory cytokines, and re-epithelialization related genes in the fish skin. Furthermore, significant decreases in pro-inflammatory cytokines expression were detected in fish from SP group, respect to control ones. Overall, SpPdp11 inclusion facilitated the wound healing and the re-epithelialization of the damaged skin, alleviated the inflammatory response in the wound area through intensifying the antioxidant system, and enhancing the neo-vascularization and the synthesis of matrix proteins in the skin wound sites of fish.

Influence of skin wounds on the intestinal inflammatory response and barrier function: Protective role of dietary Shewanella putrefaciens SpPdp11 administration to gilthead seabream (Sparus aurata L.)

The effects of skin wounds on the intestinal barrier function and the beneficial effects of the dietary administration of Shewanella putrefaciens (known as SpPdp11) in gilthead seabream (Sparus aurata L.) were studied. Two replicates of fish were fed a commercial diet (control, CON) or CON diet enriched with 10⁹ cfu g^-1 SpPdp11 (SP diet) for 30 days. After this time, half of the fish were sampled, while the others were injured below the lateral line (wounded fish, W) and fed the same diets for an extra week before sampling (CON + W and SP + W groups). The intestinal histology and gene expression of different genes relevant for the intestinal barrier function were studied. The results showed that injured fish had a disordered enterocyte nucleus disposition, a more intense infiltration of mixed leucocytes and a thicker lamina propria in the intestine compared to the control fish. However, the fish in the SP + W group did not present these pathological symptoms in the intestine. No significant variations in the number of goblet cells were detected among the different experimental groups. Pro-inflammatory cytokines (colony-stimulating factor receptor 1, CSF1R, myeloperoxidase, MPO and interleukin-1β, IL-1β), mucins (intestinal mucin, IMUC and mucin 2, MUC2), and immunoglobulin T heavy chain (IGHT) were up-regulated, while tight junction protein occludin was down-regulated in the intestine from fish of the CON + W group. Similarly, the dietary administration of SpPdp11 markedly depressed the gene expression of pro-inflammatory cytokines, MUC2 and IGHT, but increased the gene expression of anti-inflammatory cytokine transforming growth factor-β1 (TGF-β1) and the tight junction proteins tricellulin and occluding after wounding. In brief, the skin wounds provoked an intestinal inflammatory response that included changes in the mucus layer and tight junction disruptions. Besides this, preventive administration of SpPdp11 alleviated the intestinal dysfunctions caused by skin wounds in gilthead seabream.

Probiotic effects of mixture of Groenewaldozyma salmanticensis and Gluconacetobacter liquefaciens on growth and immune responses in Paralichthys olivaceus

This study was performed to evaluate the effects of dietary probiotics on growth, non-specific immune responses and disease resistance in olive flounder, Paralichthys olivaceus. During 8 weeks, the fish were fed the five experimental diets such as a basal commercial diet (CON), oxytetracycline (OTC) and three basal diets containing Bacillus subtilis (BS), a commercial microbial product (CES) and a mixture of yeast and bacterium (PI), respectively. Fish fed all the probiotics diets and OTC showed a significantly higher growth than fish-fed CON (P < 0·05). Fish-fed PI had a significantly higher nitroblue tetrazolium activity, whereas fish-fed CES showed a higher lysozyme level (P < 0·05). A 7-day challenge test also showed that fish-fed PI had a cumulative survival rate equivalent to that of fish-fed OTC (P < 0·05). Moreover, the diet (PI) appeared to increase the diversity of microbial community in the fish. All these results suggest that the probiotics diet could function as a potential antibiotic replacer in the olive flounder. SIGNIFICANCE AND IMPACT OF THE STUDY: This study is unique in revealing that a diet mixture of yeast, Groenewaldozyma salmanticensis and bacterium Gluconacetobacter liquefaciens can enhance growth, innate immunity and diversity of microbial community including dominant species in the olive flounder. All these indicate that the diet mixture could function as a potential antibiotic replacer in one of the most commercially important fisheries in South Korea.

Modulation of transcriptomic profile in aquatic animals: Probiotics, prebiotics and synbiotics scenarios

Aquaculture and fisheries have provided protein sources for human consumption for a long time, but diseases have induced declines in product benefits and raised concerns, resulting in great losses to these industries in many countries. The overuse of antibiotics for the treatment of diseases has increased the chemical concentrations in culture systems and weakened the natural immunity of aquatic organisms. Concerns regarding the detrimental effects of antibiotics on the environment and human health due to residual antibiotic-related issues encourage the development of reliable, environmental and health safety methods, such as vaccines, probiotics, prebiotics, synbiotics and phytobiotics, for protection against disease and for reducing and possibly eliminating disease occurrence. Immunity has been effectively enhanced by pro-, pre-, and synbiotics, which confer strong protection and reduce the risks associated with stressors and disease outbreaks in culture systems. These agents confer several benefits, including enhancing both host growth and immune responses against pathogens, while sustaining health and environmental stability, and their use is thus widely accepted. Alterations in gene expression in individual cells could serve as an indicator of the immunity and growth rate of aquatic animals after pro-, pre- and synbiotic feeding. This review addresses the potential use of pro, pre- and synbiotics as immunostimulants for improved aquaculture management and environmental health and chronicles the recent insights regarding the application of pro-, pre- and synbiotics with special emphasis on their immunomodulatory and antioxidative responses based on gene expression changes. Furthermore, the current review describes the research gaps and other issues that merit further investigation.

TarSynFlow, a workflow for bacterial genome comparisons that revealed genes putatively involved in the probiotic character of Shewanella putrefaciens strain Pdp11

Probiotic microorganisms are of great interest in clinical, livestock and aquaculture. Knowledge of the genomic basis of probiotic characteristics can be a useful tool to understand why some strains can be pathogenic while others are probiotic in the same species. An automatized workflow called TarSynFlow (Targeted Synteny Workflow) has been then developed to compare finished or draft bacterial genomes based on a set of proteins. When used to analyze the finished genome of the probiotic strain Pdp11 of Shewanella putrefaciens and genome drafts from seven known non-probiotic strains of the same species obtained in this work, 15 genes were found exclusive of Pdp11. Their presence was confirmed by PCR using Pdp11-specific primers. Functional inspection of the 15 genes allowed us to hypothesize that Pdp11 underwent genome rearrangements spurred by plasmids and mobile elements. As a result, Pdp11 presents specific proteins for gut colonization, bile salt resistance and gut pathogen adhesion inhibition, which can explain some probiotic features of Pdp11.

Modulation of Intestinal Microbiota in Solea senegalensis Fed Low Dietary Level of Ulva ohnoi

Gastrointestinal (GI) microbiota has a relevant role in animal nutrition, modulation of the immune system and protection against pathogen invasion. Interest in algae as source of nutrients and functional ingredients for aquafeeds is increasing in order to substitute conventional feedstuffs by more sustainable resources. The diet is an important factor in the modulation of the microbiota composition, and functional ingredients have been proposed to shape the microbiota and contribute benefits to the host. However, fish microbiome research is still limited compared to other hosts. Solea senegalensis is a flat fish with high potential for aquaculture in South Europe. In this study, a characterization of the microbiome of S. senegalensis (GI) tract and the effects of feeding Ulva ohnoi supplemented diet has been carried out. Differences in the composition of the microbiota of anterior and posterior sections of S. senegalensis GI tract have been observed, Pseudomonas being more abundant in the anterior sections and Mycoplasmataceae the dominant taxa in the posterior GI tract sections. In addition, modulation of the GI microbiota of juvenile Senegalese sole fed for 45 days a diet containing low percentage of U. ohnoi has been observed in the present study. Microbiota of the anterior regions of the intestinal tract was mainly modulated, with higher abundance of Vibrio spp. in the GI tract of fish fed dietary U. ohnoi.

Dietary administration of the probiotic Shewanella putrefaciens Pdp11 promotes transcriptional changes of genes involved in growth and immunity in Solea senegalensis larvae

Senegalese sole (Solea senegalensis) has been proposed as a high-potential species for aquaculture diversification in Southern Europe. It has been demonstrated that a proper feeding regimen during the first life stages influences larval growth and survival, as well as fry and juvenile quality. The bacterial strain Shewanella putrefaciens Pdp11 (SpPdp11) has shown very good probiotic properties in Senegalese sole, but information is scarce about its effect in the earliest stages of sole development. Thus, the aim of this study was to investigate the effect of SpPdp11, bioencapsulated in live diet, administered during metamorphosis (10-21 dph) or from the first exogenous feeding of Senegalese sole (2-21 dph). To evaluate the persistence of the probiotic effect, we sampled sole specimens from metamorphosis until the end of weaning (from 23 to 73 dph). This study demonstrated that probiotic administration from the first exogenous feeding produced beneficial effects on Senegalese sole larval development, given that specimens fed this diet exhibited higher and less dispersed weight, as well as increases in both total protein concentration and alkaline phosphatase activity, and in non-specific immune response. Moreover, real-time PCR documented changes in the expression of a set of genes involved in central metabolic functions including genes related to growth, genes coding for proteases (including several digestive enzymes), and genes implicated in the response to stress and in immunity. Overall, these results support the application of SpPdp11 in the first life stages of S. senegalensis as an effective tool with the clear potential to benefit sole aquaculture.

Effects of probiotic Bacillus as a substitute for antibiotics on antioxidant capacity and intestinal autophagy of piglets

The objective of this study was to evaluate effects of probiotic Bacillus amyloliquefaciens (Ba) as a substitute for antibiotics on growth performance, antioxidant ability and intestinal autophagy of piglets. Ninety piglets were divided into three groups: G1 (containing 150 mg/Kg aureomycin in the diet); G2 (containing 75 mg/Kg aureomycin and 1 × 10⁸ cfu/Kg Ba in the diet); G3 (containing 2 × 10⁸ cfu/Kg Ba in the diet without any antibiotics). Each treatment had three replications of ten pigs per pen. Results showed that Ba replacement significantly increased the daily weight gain of piglets. Moreover, improved antioxidant status in serum and jejunum was noted in Ba-fed groups as compared with aureomycin group. Increased gene expression of antioxidant enzymes and elevated nuclear factor erythroid 2 related factor 2 (Nrf2) in jejunum was also observed in Ba-fed groups. Besides, Ba replacement significantly decreased jejunal c-Jun N-terminal kinase (JNK) phosphorylation compared with antibiotic group. Western blotting results also revealed that replacing all antibiotics with Ba initiated autophagy in the jejunum as evidenced by increased microtubule-associated protein 1 light chain 3 II (LC3-II) abundance. Taken together, these results indicate that replacing aureomycin with Ba can improve growth performance and antioxidant status of piglets via increasing antioxidant capacity and intestinal autophagy, suggesting a good potential for Ba as an alternative to antibiotics in feed.

Solea senegalensis sperm cryopreservation: New insights on sperm quality

Cryopreservation of Senegalese sole sperm can represent an alternative to overcome some reproductive problems of this species. However, it is important to guarantee the safe use of cryopreserved sperm by selecting an appropriate protocol according to a high demand quality need to be ensured. It has been demonstrated that traditional assays such as motility and viability do not provide enough information to identify specific damage caused by cryopreservation process (freezing and thawing). Specific tests, including lipid peroxidation and DNA damage, should be performed. In the present study, motility and lipid peroxidation were performed as specific tests allowing us to discard cryopreservation conditions such as methanol as internal cryoprotectant and bovine serum albumin as external cryoprotectant. In addition, a caspase 3/7 detection by flow cytometry was performed to analyze apoptosis activity in the best selected conditions. Moreover, new highly sensitive tests based on transcript number detection have recently been described in fish sperm cryopreservation. For this reason, a transcript level detection assay was performed on certain oxidative and chaperone genes related to fertilization ability and embryo development (hsp70, hsp90BB, hsp90AA, gpx) to select the best cryopreservation conditions. DMSO+ egg yolk proved to be the best cryoprotectant combination in terms of transcript level. This study describes an optimized cryopreservation protocol for Solea senegalensis sperm demonstrating for the first time that transcript degradation is the most sensitive predictor of cell status in this species after cryopreservation.

Terminal carbohydrates abundance, immune related enzymes, bactericidal activity and physico-chemical parameters of the Senegalese sole (Solea senegalensis, Kaup) skin mucus

Recently, interest in mucosal surfaces, more specifically fish skin and its secreted mucus, has greatly increased among immunologists. The abundance of terminal carbohydrates, several enzymes (proteases, lysozyme, peroxidase, alkaline phosphatase, esterases and ceruloplasmin), bactericidal activity against fish pathogenic and non-pathogenic bacteria and several physico-chemical parameters (protein concentration, pH, conductivity, redox potential, osmolarity, density and viscosity) in the skin mucus of Senegalese sole (Solea senegalensis, Kaup) have been evaluated. Present results evidence the abundance of N-acetylneuraminic acid, mannose, glucose and N-acetyl-galactosamine in skin mucus. The levels of lysozyme, proteases, esterases and alkaline phosphatase were very similar (from 20 to 30 Units mg^-1 protein). However, 93 Units mg^-1 protein were detected of ceruloplasmin and only 4'88 Units mg^-1 protein of peroxidase. Skin mucus of S. senegalensis showed high bactericidal activity against the tested pathogen bacteria but weak activity against non-pathogenic bacteria. Finally, a clear relationship between mucus density and temperature was detected, while viscosity showed a direct shear- and temperature-dependent behaviour. These results could be useful for better understanding the role of the skin mucus as a key component of the innate immune system, as well as, for elucidating possible relationships between biological and physico-chemical parameters and disease susceptibility.

Effects on intestinal microbiota and immune genes of Solea senegalensis after suspension of the administration of Shewanella putrefaciens Pdp11

The interaction host-intestinal microbiota is essential for the immunological homeostasis of the host. Probiotics, prebiotics and synbiotics are promising tools for the manipulation of the intestinal microbiota towards beneficial effects to the host. The objective of this study was to evaluate the modulation effect on the intestinal microbiota and the transcription of genes involved in the immune response in head kidney of Solea senegalensis after administration of diet supplemented with the prebiotic alginate and the probiotic Shewanella putrefaciens Pdp11 CECT 7627 (SpPdp11). The results showed higher adaptability to dietary changes in the intestinal microbiota of fish fed diet with alginate and SpPdp11 together compared to those fish that received an alginate-supplemented diet. The alginate-supplemented diet produced up-regulation of genes encoding proteins involved in immunological responses, such as complement, lysozyme G and transferrin, and oxidative stress, such as NADPH oxidase and glutation peroxidase. On the other hand, the administration of alginate combined with SpPdp11 resulted in a significant increase of the transcription of genes encoding for glutation peroxidase and HSP70, indicating a potential protective effect of SpPdp11 against oxidative stress. In addition, these effects were maintained after the suspension of the probiotic treatment. The relationship between the modulation of the intestinal microbiota and the expression of genes with protective effect against the oxidative stress was demonstrated by the Principal Components Analysis.

Dietary peppermint (Mentha piperita) extracts promote growth performance and increase the main humoral immune parameters (both at mucosal and systemic level) of Caspian brown trout (Salmo trutta caspius Kessler, 1877)

The effects of dietary administration of peppermint (Mentha piperita L.) on Caspian brown trout fish (Salmo trutta caspius) were studied. Fish were divided into 4 groups before being fed diets supplemented with 0% (control), 1%, 2% and 3% of peppermint extracts for 8 weeks. Dose-dependent increases in growth, immune (both in skin mucus and blood serum) and hematological parameters (number of white cells, hematocrit and hemoglobin content), as well as in amylase activity and in the number of lactic acid bacteria on intestine were recorded in fish fed supplemented diets compared to control fish. However, the dietary peppermint supplements have different effects on the number of blood leucocytes depending on the leukocyte cell type. While no significant differences were observed in the number of blood monocytes and eosinophils, the number of lymphocytes was decreased, respectively, on fish fed peppermint enriched diets, respect to the values found in control fish. Furthermore, dietary peppermint supplements have no significant effect on blood biochemical parameters, enzymatic activities of liver determined in serum and total viable aerobic bacterial count on intestine of Caspian brown trout. Present results support that dietary administration of peppermint promotes growth performance and increases the main humoral immune parameters (both at mucosal and systemic level) and the number of the endogenous lactic acid bacteria of Caspian brown trout. This study underlying several positive effects of dietary administration of peppermint to farmed fish.