The advancement of probiotics research and its application in fish farming industries

Isolation and identification of probiotic Bacillus subtilis AJQ03 from the intestinal tract of Anguilla japonica (Japanese eel)

In recent years, the use of fish-derived probiotics in aquaculture has become more widespread. However, research on Anguilla japonica-derived probiotics is still limited. To evaluate the potential of probiotics for disease control in eel aquaculture, isolates were obtained from the intestinal tract of healthy Anguilla japonica. These isolates were assessed for their adhesion properties, inhibition of pathogen adhesion, and hydrolytic enzyme production. Morphological characteristics and 16S rRNA sequence analysis were used for identification. Results showed that the AJQ03 strain adhered to the intestinal mucus and inhibited common pathogenic bacteria through adhesion inhibition, and further produced amylase, lipase, protease, and cellulase. Based on morphological characteristics and 16S rRNA sequencing, AJQ03 was identified as Bacillus subtilis. The strain demonstrated tolerance to various extreme conditions, as well as survival in simulated gastrointestinal fluids and superior growth in intestinal fluid compared to Luria-Bertani (LB) broth. In vitro safety tests showed that AJQ03 was not resistant to 32 antibiotics and exhibited γ hemolysis on blood plate. In vivo safety tests demonstrated a 100% survival rate for the fish, with stable organ indices, reduced bacterial loads in the liver and spleen, and complete bacterial clearance by day 7 without residue. Intestinal bacterial load results confirmed effective colonization by strain AJQ03. Analysis of the impact of AJQ03 on the gut microbiota of A. japonica revealed a significant increase in the relative abundance of Bacillus at the genus level, corroborating the colonization efficiency of AJQ03. Additionally, the relative abundances of Klebsiella, Pseudomonas, and Aeromonas were significantly lower compared to the controls, indicating that strain AJQ03 effectively reduced harmful bacteria and improved gut microbiota composition. This study confirms that B. subtilis AJQ03, isolated from the intestine of A. japonica, can serve as a probiotic candidate in A. japonica aquaculture.

Exploring the protective role of Bacillus velezensis BV1704-Y in zebrafish health and disease resistance against Aeromonas hydrophila infection

Bacillus genus, particularly Bacillus velezensis, is increasingly considered as viable alternatives to antibiotics in aquaculture due to their safety and probiotic potential. However, the specific mechanisms through which probiotic B. velezensis confers protection against Aeromonas hydrophila infection in fish remain poorly understood. This study delved into the multifaceted impacts of B. velezensis BV1704-Y on diverse facets of zebrafish health, including gut barrier function, immune response, oxidative stress, gut environment, microbiome composition, and disease resistance. Our findings demonstrate that supplementation with B. velezensis BV1704-Y significantly alleviated symptoms and reduced mortality in zebrafish infected with A. hydrophila. Furthermore, a notable reduction in the expression of pivotal immune-related genes, such as IL-1β, IL6, and TNF-α, was evident in the gut and head kidney of zebrafish upon infection. Moreover, B. velezensis BV1704-Y supplementation resulted in elevated activity levels of essential antioxidant enzymes, including SOD, CAT, and GSH, in gut tissue. Notably, B. velezensis BV1704-Y positively modulated the structure and function of the intestinal microbiome, potentially enhancing immune response and resilience in zebrafish. Specifically, supplementation with B. velezensis BV1704-Y promoted the relative abundance of beneficial bacteria, such as Cetobacterium, which showed a noteworthy negative correlation with the expression of pro-inflammatory genes and a positive correlation with gut barrier-related genes. Altogether, our study suggests that B. velezensis BV1704-Y holds promise as an effective probiotic for protecting zebrafish against A. hydrophila infection, offering potential benefits for the aquaculture industry.

Antimicrobial Resistance in Aquaculture: Risk Mitigation within the One Health Context

The application of antimicrobials in aquaculture primarily aims to prevent and treat bacterial infections in fish, but their inappropriate use may result in the emergence of zoonotic antibiotic-resistant bacteria and the subsequent transmission of resistant strains to humans via food consumption. The aquatic environment serves as a potential reservoir for resistant bacteria, providing an ideal breeding ground for development of antimicrobial resistance (AMR). The mutual inter-connection of intensive fish-farming systems with terrestrial environments, the food processing industry and human population creates pathways for the transmission of resistant bacteria, exacerbating the problem further. The aim of this study was to provide an overview of the most effective and available risk mitigation strategies to tackle AMR in aquaculture, based on the One Health (OH) concept. The stringent antimicrobial use guidelines, promoting disease control methods like enhanced farm biosecurity measures and vaccinations, alternatives to antibiotics (ABs) (prebiotics, probiotics, immunostimulants, essential oils (EOs), peptides and phage therapy), feeding practices, genetics, monitoring water quality, and improving wastewater treatment, rather than applying excessive use of antimicrobials, can effectively prevent the development of AMR and release of resistant bacteria into the environment and food. The contribution of the environment to AMR development traditionally receives less attention, and, therefore, environmental aspects should be included more prominently in OH efforts to predict, detect and prevent the risks to health. This is of particular importance for low and middle-income countries with a lack of integration of the national AMR action plans (NAPs) with the aquaculture-producing environment. Integrated control of AMR in fisheries based on the OH approach can contribute to substantial decrease in resistance, and such is the case in Asia, where in aquaculture, the percentage of antimicrobial compounds with resistance exceeding 50% (P50) decreased from 52% to 22% within the period of the previous two decades.

Multi-Omics Analysis Reveals the Regulatory Mechanism of Different Probiotics on Growth Performance and Intestinal Health of Salmo trutta (S. trutta)

Probiotics play an important role in animal production, providing health benefits to the host by improving intestinal microbial balance. In this study, we added three different probiotics, Saccharomyces cerevisiae (SC), Bacillus licheniformis (BL), and lactic acid bacteria (LAB), and compared them with the control group (CON), to investigate the effects of probiotic supplementation on growth performance, gut microbiology, and gut flora of S. trutta. Our results showed that feeding probiotics improved the survival, growth, development, and fattening of S. trutta. Additionally, probiotic treatment causes changes in the gut probiotic community, and the gut flora microorganisms that cause significant changes vary among the probiotic treatments. However, in all three groups, the abundance of Pseudomonas, Acinetobacter, and Rhizophagus bacterial genera was similar to that in the top three comparative controls. Furthermore, differences in the composition of intestinal microbiota among feed types were directly associated with significant changes in the metabolomic landscape, including lipids and lipid-like molecules, organic acids and derivatives, and organoheterocyclic compounds. The probiotic treatment altered the gut microbiome, gut metabolome, and growth performance of S. trutta. Using a multi-omics approach, we discovered that the addition of probiotics altered the composition of gut microbiota, potentially leading to modifications in gut function and host phenotype. Overall, our results highlight the importance of probiotics as a key factor in animal health and productivity, enabling us to better evaluate the functional potential of probiotics.

Removal of sarafloxacin from aqueous solution through Ni/Al-layered double hydroxide@ZIF-8

In recent years, excessive amounts of drugs such as antibiotics have been used to combat COVID-19 and newly discovered viruses. This has led to the production and release of significant amounts of drugs and their metabolites as toxic pollutants in aquatic systems. Therefore, pharmaceutical wastes must be removed efficiently before entering the environment and entering water sources. In this research, Ni/Al-LDH@ZIF-8 nanocomposite was synthesized from layered double hydroxides and metal-organic frameworks and used to remove the antibiotic sarafloxacin (SRF) in the aqueous medium. The work aimed to develop the performance and combine the features of the adsorbent compounds such as high surface area, adjustable porosity, and low-density structure. Different methods implemented to analyze the nanocomposite, such as Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, and energy dispersive X-ray spectroscopy. The experiment utilized the central composite design to evaluate statistics and the response level method to optimize the factors affecting the absorption process. The initial concentration of SRF, adsorbent dose, pH, and contact time were considered in this experiment. The results showed an increase in the removal efficiency of SRF to 97%. Statistical studies showed that the optimal adsorption conditions are as follows: initial concentration of SRF 40 mg·L-1, pH 6.3, adsorbent dose of Ni/Al-LDH@ZIF-8 49 mg, and contact time of 44 min. According to the model of isotherms parameters, the adsorption process is more consistence with the Freundlich model with the absorption capacity of 79.7 mg·g-1. The pseudo-second-order model described the adsorption kinetics data.

Graphical abstract

In Vitro Profiling of Potential Fish Probiotics, Enterococcus hirae Strains, Isolated from Jade Perch, and Safety Properties Assessed Using Whole Genome Sequencing

The demands of intensified aquaculture production and escalating disease prevalence underscore the need for efficacious probiotic strategies to enhance fish health. This study focused on isolating and characterising potential probiotics from the gut microbiota of the emerging aquaculture species jade perch (Scortum barcoo). Eighty-seven lactic acid bacteria and 149 other bacteria were isolated from the digestive tract of five adult jade perch. The screening revealed that 24 Enterococcus hirae isolates inhibited the freshwater pathogens Aeromonas sobria and Streptococcus iniae. Co-incubating E. hirae with the host gut suspensions demonstrated a two- to five-fold increase in the size of growth inhibition zones compared to the results when using gut suspensions from tilapia (a non-host), indicating host-specificity. Genome analysis of the lead isolate, E. hirae R44, predicted the presence of antimicrobial compounds like enterolysin A, class II lanthipeptide, and terpenes, which underlay its antibacterial attributes. Isolate R44 exhibited desirable probiotic characteristics, including survival at pH values within the range of 3 to 12, bile tolerance, antioxidant activity, ampicillin sensitivity, and absence of transferable antimicrobial resistance genes and virulence factors commonly associated with hospital Enterococcus strains (IS16, hylEfm, and esp). This study offers a foundation for sourcing host-adapted probiotics from underexplored aquaculture species. Characterisation of novel probiotics like E. hirae R44 can expedite the development of disease mitigation strategies to support aquaculture intensification.

Probiotic performance of B. subtilis MS. 45 improves aquaculture of rainbow trout Oncorhynchus mykiss during acute hypoxia stress

The aim of this study was to produce mutant strains of Bacillus subtilis with high probiotic performance for use in the aquaculture of rainbow trout Oncorhynchus mykiss. The main strain of B. subtilis (MS) was irradiated with gamma rays (5.3 KGy). Subsequently, the B. subtilis mutant strain no. 45 (MS. 45) was selected for bacterial growth performance, resistance to acidic conditions, resistance to bile salts and antibacterial activity against Aeromonas hydrophila and Pseudomonas fluorescens. After 60 days, the rainbow trout (70.25 ± 3.89 g) fed with MS. 45 and MS were exposed to hypoxia stress (dissolved oxygen = 2 ppm). Subsequently, immune indices (lysozyme, bacterial activity and complement activity), hematological indices [hematocrit, hemoglobin, WBC, RBC, mean corpuscular volume (MCV)] and antioxidant factors (T-AOC, SOD and MDA)) were analyzed after and before hypoxia exposure. The expression of immunological genes (IFN-γ, TNF-α, IL-1β, IL-8) in the intestine and the expression of hypoxia-related genes (HIF-1α, HIF-2α, FIH1) in the liver were compared between the different groups under hypoxia and normoxia conditions. Growth, immunological and antioxidant indices improved in group MS. 45 compared to the other groups. Stress indices and associated immunologic and hypoxia expressions under hypoxia and normoxia conditions improved in MS. 45 compared to the other groups. This resulted in improved growth, immunity and stress responses in fish fed with the microbial supplement of MS. 45 (P < 0.05) under hypoxia and normoxia conditions, (P < 0.05), resulting in a significant improvement in trout aquaculture.

A native strain of Bacillus subtilis increases lipid accumulation and modulates expression of genes related to digestion and amino acid metabolism in Litopenaeus vannamei

In the field of shrimp aquaculture, the utilization of probiotics represents a promising avenue, due to the well-documented benefits conferred by these microorganisms. In the current study, a Bacillus subtilis strain, referred to as strain E, was isolated from the gastrointestinal tract of the shrimp Litopenaeus vannamei and subsequently identified via molecular methods and phylogeny. The probiotic potential of strain E was characterized, and its application as a feed shrimp additive was evaluated in a 45-day experiment. Several parameters were assessed, including zootechnical performance, muscle tissue proximate composition, hepatopancreas lipid concentration, and the expression of genes associated with digestion, amino acid metabolism, and antioxidant defense mechanisms in various shrimp tissues. Although no significant impact on zootechnical performance was observed, supplementation with strain E led to an increase in lipid concentration within both muscle and hepatopancreas tissues. Furthermore, a marked decrease in the expression of genes linked to digestion and amino acid metabolism was noted. These findings suggest that the addition of the B. subtilis strain E to shrimp feed may enhance nutrient absorption and modulate the expression of genes related to digestion and amino acid metabolism.

Effects of Bacillus subtilis as a single strain probiotic on growth, disease resistance and immune response of striped catfish (Pangasius hypophthalmus)

The present study investigated the potential role of Bacillus subtilis as probiotic in striped catfish (Pangasius hypophthalmus). Fish (initial weight = 150.00±2.63g n = 180) were stocked in circular tanks. Four isonitrogenous (30%) and isolipidic (3.29%) diets were formulated having supplementation of B. subtilis at four different levels (P0; 0, P1: 1×106, P2: 1×108 and P3: 1×1010 CFU/g). Each treatment had three replicates, while each replicate had fifteen fish. The trial started on second week of July and continued for eight weeks. Growth, feed conversion ratio, crude protein content, the concentration of amylase and protease, the profile of both dispensable and non-dispensable amino acids in all four dietary groups increased with a gradual increase of B. subtilis in the diet. At the end of growth experiment, fish in all four groups were exposed to Staphylococcus aureus (5×105 CFU/ml). After S. aureus challenge, fish fed with B. subtilis responded better to damage caused by reactive oxygen species and lipid peroxidation and better survival rate. The catalase and superoxide dismutase level also increased in response to bacterial challenge in B. subtilis fed groups. On the other hand, the concentration of malondialdehyde gradually decreased in these groups (+ve P0 >P1>P2>P3). It is concluded that supplementation of B. subtilis as a probiotic improved the growth, protein content, antioxidant response and immunocompetency against S. aureus in striped catfish. The optimum dosage of B. subtilis, at a concentration of 1×1010 CFU/g, resulted in the most favorable outcomes in striped catfish. This single bacterial strain can be used as an effective probiotic in large scale production of aquafeed for striped catfish. Future studies can investigate this probiotic's impact in the intensive culture of the same species.

Dietary supplementation of Polygonum chinense improves the immunity of Asian seabass, Lates calcarifer (Bloch, 1790) against Vibrio harveyi infection

Aquaculture plays a significant role in the overall fish production in Malaysia, contributing a substantial quantity of food-fish amounting to roughly 573,683 tonnes with an estimated economic value of US$860 million in 2022. However, diseases have become a significant limitation for aquaculture production. Therefore, herbal immunostimulant has been considered a natural and practical approach of preventing disease infection in fish. The ability of Polygonum chinense extract (PCE) on haemato-biochemistry parameters, immunomodulatory properties, and disease resistance of Lates calcarifer (Asian seabass) under Vibrio harveyi challenge was evaluated in this study, with a focus on dose-response associations and variability over various exposure durations (0-, 7- and 14-day post-infection). A total of 480 Asian seabass (9.5 ± 0.2 g) were distributed in 12 aquaria and fed four diets supplemented with 0 (control), 2, 5 and 10 g/kg diet for 60 days before being challenged with V. harveyi. Dietary PCE significantly improved (P < 0.05) survival, with the dose of 10 g/kg showing the highest survival rate (90 %) when compared to the control (60 %). Additionally, hematological (red and white blood cell counts, hemoglobulin, packed cell volume, and mean corpuscular volume) and immunological (activities of lysozyme, phagocytic activity and respiratory burst, and serum total immunoglobulin) properties were significantly increased (P < 0.05) in comparison to the control group. In contrast, serum aspartate aminotransferase and alanine aminotransferase levels, as well as glucose level were significantly reduced (P < 0.05) in PCE-fed fish compared to the control group. Conclusively, the current study discovered that supplementing fish feed with P. chinense extract improves fish haemato-biochemical profile, immunocompetence and disease resistance to V. harveyi infection.

Probiotic Supplementation as an Emerging Alternative to Chemical Therapeutics in Finfish Aquaculture: a Review

Aquaculture is a promising food sector to fulfil nutritional requirements of growing human population. Live weight aquaculture production reached up to 114.5 million tonnes in 2018 and it is further expected to grow by 32% by year 2030. Among total aquaculture production, major product harvested is finfish and its contribution has reached 46% in recent years. Frequent outbreaks of infectious diseases create obstacle in finfish production, result in economic losses to the farmers and threaten the sustainability of aquaculture industry itself. In spite of following the best management practices, the use of antibiotics, chemotherapeutics and phytochemicals often become the method of choice in finfish culture. Among these, phytochemicals have shown lesser effect in animal welfare while antibiotics and other chemotherapeutics have led to negative consequences like emergence of drug-resistant bacteria, and accumulation of residues in host and culture system, resulting in quality degradation of aqua products. Making use of probiotics as viable alternative has paved a way for sustainable aquaculture and minimise the use of antibiotics and other chemotherapeutics that pose adverse effect on host and culture system. This review paper elucidates the knowledge about antibiotics and other chemicals, compilation of probiotics and their effects on health status of finfish as well as overall culture environment. Besides, concoction of probiotics and prebiotics for simultaneous application has also been discussed briefly.

Microencapsulation of Lactobacillus plantarum in the alginate/chitosan improves immunity, disease resistance, and growth of Nile tilapia (Oreochromis niloticus)

This study evaluated the effects of microencapsulation of L. plantarum (as a probiotic) with chitosan/alginate biopolymers (MLCA) on innate immune response, disease resistance, and growth performance of Nile tilapia (Oreochromis niloticus). Four hundred and eighty fish were randomly distributed in glass tanks (150 L) and fed with diets including diet 1: control; diet 2: 10 g kg-1 microcapsules; diet 3: 108 CFU g-1 L. plantarum; and diet 4: 10 g kg-1 MLCA for 60 days. The hematology and biochemical indices, lysozyme activity, alternative complement activities, respiratory burst, serum bactericidal activity, as well as growth performance parameters (specific growth rate, feed conversion ratio) were analyzed. White blood cells, plasma protein and globulin concentration, serum lysozyme, and respiratory burst activities of fish were significantly increased (P < 0.05) in the MLCA diet. A challenge test against Streptococcus agalactiae, at the end of the experiment, showed the highest survival rate of the fish fed with MLCA. Moreover, the fish fed with MLCA showed a significant improvement in SGR (3.12 ± 0.18%) and FCR (1.23 ± 0.20) and had the highest growth performance. These results suggest longer stability of probiotics in the microcapsules, and their immunomodulatory effect can be considered a promising immunostimulant and growth enhancer in the Nile tilapia diet.

Bioassay and Whole-Genome Analysis of Bacillus velezensis FIO1408, a Biocontrol Agent Against Pathogenic Bacteria in Aquaculture

Bacterial disease is one of the most critical problems in aquaculture. Probiotics represent a promising biological approach to control bacterial disease because it is effective against pathogens and environmentally friendly. This study assessed the antagonistic activities of a bacterial strain FIO1408 isolated from deep-sea water against many pathogenic bacteria in aquaculture, including Listonella anguillarum, Vibrio parahaemolyticus, Vibrio alginolyticus, Aeromonas hydrophila, Edwardsiella anguillarum, Edwardsiella tarda, and Edwardsiella piscicida. The complete genome of strain FIO1408 consisted of a circular chromosome of 4,137,639 bp and two plasmids of 16,439 bp and 24,472 bp. Phylogenetic analysis showed strain FIO1408 clustered with Bacillus velezensis strains. 12 genes/gene clusters responsible for the synthesis of secondary metabolites were identified in the FIO1408 genome, including three lipopeptides, three polyketides, three bacteriocins, one siderophore, one dipeptide, and one unknown type. Also identified were 273 unique orthologous genes primarily involved in phage resistance, protein hydrolysis, environmental survivability, and genetic stability compared to B. velezensis KACC 13105, B. velezensis FZB42T, and B. velezensis NRRL B-41580. The principal safety of FIO1408 was demonstrated by genetic analyses and feeding trials. These findings will contribute to studies on the biocontrol mechanisms of B. velezensis FIO1408 and facilitate its application as a potent biological control agent against bacterial pathogens in aquaculture.

Probiotics and biofilm interaction in aquaculture for sustainable food security: A review and bibliometric analysis

Aquaculture is one of the most significant food sources from the prehistoric period. As aquaculture intensifies globally, the prevalence and outbreaks of various pathogenic microorganisms cause fish disease and heavy mortality, leading to a drastic reduction in yield and substantial economic loss. With the modernization of the aquaculture system, a new challenge regarding biofilms or bacterial microenvironments arises worldwide, which facilitates pathogenic microorganisms to survive under unfavorable environmental conditions and withstand various treatments, especially antibiotics and other chemical disinfectants. However, we focus on the mechanistic association between those microbes which mainly form biofilm and probiotics in one of the major food production systems, aquaculture. In recent years, probiotics and their derivatives have attracted much attention in the fisheries sector to combat the survival strategy of pathogenic bacteria. Apart from this, Bibliometric analysis provides a comprehensive overview of the published literature, highlighting key research themes, emerging topics, and areas that require further investigation. This information is valuable for researchers, policymakers, and stakeholders in determining research priorities and allocating resources effectively.

Isolation of Bacillus subtilis and Bacillus pumilus with Anti-Vibrio parahaemolyticus Activity and Identification of the Anti-Vibrio parahaemolyticus Substance

The adoption of intensive farming has exacerbated disease outbreaks in aquaculture, particularly vibriosis caused by Vibrio parahaemolyticus. The use of probiotics to control V. parahaemolyticus is recognized as a good alternative to antibiotics for avoiding the development of antibiotic-resistant bacteria. In this study, two strains of B. HLJ1 and B. C1 with strong inhibitory activity on V. parahaemolyticus were isolated from aquaculture water and identified as Bacillus subtilis and Bacillus pumilus, respectively. Both B. HLJ1 and B. C1 lacked antibiotic resistance and virulence genes, suggesting that they are safe for use in aquaculture. In addition, these two strains can tolerate acid environments, produce spores, secrete extracellular enzymes, and co-aggregate as well as auto-aggregate with V. parahaemolyticus. B. HLJ1 and B. C1 produced the same anti-V. parahaemolyticus substance, which was identified as AI-77-F and belongs to amicoumacins. Both B. C1 and B. HLJ1 showed inhibitory activity against 11 different V. parahaemolyticus and could effectively control the growth of V. parahaemolyticus in simulated aquaculture wastewater when the concentration of B. C1 and B. HLJ1 reached 1 × 10⁷ CFU/mL. This study shows that B. HLJ1 and B. C1 have great potential as aquaculture probiotics.

Therapeutic Prospect of New Probiotics in Neurodegenerative Diseases

Increasing clinical and preclinical evidence implicates gut microbiome (GM) dysbiosis as a key susceptibility factor for neurodegenerative disorders, including Alzheimer's disease (AD) and Parkinson's disease (PD). In recent years, neurodegenerative diseases have been viewed as being driven not solely by defects in the brain, and the role of GM in modulating central nervous system function via the gut-brain axis has attracted considerable interest. Encouraged by current GM research, the development of new probiotics may lead to tangible impacts on the treatment of neurodegenerative disorders. This review summarizes current understandings of GM composition and characteristics associated with neurodegenerative diseases and research demonstrations of key molecules from the GM that affect neurodegeneration. Furthermore, applications of new probiotics, such as Clostridium butyricum, Akkermansia muciniphila, Faecalibacterium prausnitzii, and Bacteroides fragilis, for the remediation of neurodegenerative diseases are discussed.

Effects of Aeromonas hydrophila infection on the intestinal microbiota, transcriptome, and metabolomic of common carp (Cyprinus carpio)

Aeromonas hydrophila frequently has harmful effects on aquatic organisms. The intestine is an important defense against stress. In this study, we investigated the intestinal microbiota and transcriptomic and metabolomic responses of Cyprinus carpio subjected to A. hydrophila infection. The results showed that obvious variation in the intestinal microbiota was observed after infection, with increased levels of Firmicutes and Bacteroidetes and decreased levels of Proteobacteria. Several genera of putatively beneficial microbiota (Cetobacterium, Bacteroides, and Lactobacillus) were abundant, while Demequina, Roseomonas, Rhodobacter, Pseudoxanthomonas, and Cellvibrio were decreased; pathogenic bacteria of the genus Vibrio were increased after microbiota infection. The intestinal transcriptome revealed several immune-related differentially expressed genes associated with the cytokines and oxidative stress. The metabolomic analysis showed that microbiota infection disturbed the metabolic processes of the carp, particularly amino acid metabolism. This study provides insight into the underlying mechanisms associated with the intestinal microbiota, immunity, and metabolism of carp response to A. hydrophila infection; eleven stress-related metabolite markers were identified, including N-acetylglutamic acid, capsidiol, sedoheptulose 7-phosphate, prostaglandin B1, 8,9-DiHETrE, 12,13-DHOME, ADP, cellobiose, 1H-Indole-3-carboxaldehyde, sinapic acid and 5,7-dihydroxyflavone.

Functional properties of lactic acid bacteria isolated from Tilapia (Oreochromis niloticus) in Ivory Coast

BACKGROUND

Probiotics have recently been applied in aquaculture as eco-friendly alternatives to antibiotics to improve fish health, simultaneously with the increase of production parameters. The present study aimed to investigate the functional potential of lactic acid bacteria (LAB) isolated from the gut of Tilapia (Oreochromis niloticus) originating from the aquaculture farm of Oceanologic Research Center in Ivory Coast.

RESULTS

Twelve LAB strains were identified by 16 S rDNA gene sequence homology analysis belonging to two genera Pediococcus (P. acidilactici and P. pentosaceus) and Lactobacillus (L. plantarum) with a predominance of P. acidilactici. Several aspects including functional, storage, and safety characteristics were taken into consideration in the selection process of the native LAB isolates as potential probiotics. All LAB isolates showed high antagonistic activity against bacterial pathogens like Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus mirabilis, and Staphylococcus aureus. In addition, the LAB isolates exhibited different degrees of cell surface hydrophobicity in the presence of hexane, xylene, and chloroform as solvents and a good ability to form biofilm. The strong antioxidant activity expressed through the DPPH scavenging capacity of LAB intact cells and their cell-free supernatants was detected. LAB strains survived between 34.18% and 49.9% when exposed to low pH (1.5) and pepsin for 3 h. In presence of 0.3% bile salts, the growth rate ranged from 0.92 to 21.46%. Antibiotic susceptibility pattern of LAB isolates showed sensitivity or intermediate resistance to amoxicillin, cephalothin, chloramphenicol, imipenem, kanamycin, penicillin, rifampicin, streptomycin, tetracycline and resistance to oxacillin, gentamicin, and ciprofloxacin. No significant difference in antibiotic susceptibility pattern was observed between P. acidilactici and P. pentosaceus strains. The non-hemolytic activity was detected. Following the analysis of the enzyme profile, the ability of LAB isolates to produce either lipase or β-galactosidase or both enzymes was highlighted. Furthermore, the efficacy of cryoprotective agents was proved to be isolate-dependent, with LAB isolates having a high affinity for D-sorbitol and sucrose.

CONCLUSION

The explored LAB strains inhibited the growth of pathogens and survived after exposure to simulated gastrointestinal tract conditions. The safety and preservative properties are desirable attributes of these new probiotic strains hence recommended for future food and feed applications.

Characterization of Bacillus spp. isolated from the intestines of Rhynchocypris lagowskii as a potential probiotic and their effects on fish pathogens

Probiotics sourced from fish intestinal microbiota have a merit over other bacterial sources due to colonization ability and effective time. This study aimed to evaluate the bacilli isolated from the Rhynchocypris lagowskii intestines and their validity as a probiotic. Three isolates were selected (LSG 2-5, LSG 3-7, and LSG 3-8) and defined by morphological and 16S rRNA analysis as Bacillus velezensis, Bacillus aryabhattai, and Bacillus mojavensis, respectively. Results showed the strain tolerant abilities to gastrointestinal fluid, bile salt, pH, and temperature expotures. Additionally, all bacterial strains showed anti-pathogenic activity against at least four strains out of six tested pathogen strains (Staphylococcus aureus, Aeromonas hydrophila, Escherichia coli, Aeromonas veronii, Edwardsiella, and Aeromonas sobria). The bacterial strains also showed a high percentage of co-aggregation activity, more than 70%, with Aer. hydrophile, Staph. epidermidis, and Klebsiella aerogenes. At the same time, the results of competition, rejection, and substitution activity with Aer. hydrophila and Aer. veronii indicated the ability of the isolated strains to reduce the adhesion of pathogens to mucin. All strains showed safety properties, non-hemolytic, and sensitivity characteristics for most of tested antibiotics. In vivo test after injecting these strains into fish at various concentrations showed no side effects in the internal or external organs of fish compared to controls, proving that this is safe for these fish. Furthermore, the three strains produced lipase, amylase, and protease enzymes. The strains also showed bile salt hydrolase activity and biofilm formation, allowing them to tolerate stressful conditions. Conclusion: Based on these strains characteristics and features, they could be considered a promising candidate probiotic and can be used as an anti-pathogenic, especially in aquaculture.

Successional Changes of Microbial Communities and Host-Microbiota Interactions Contribute to Dietary Adaptation in Allodiploid Hybrid Fish

Host-microbiota interactions play critical roles in host development, immunity, metabolism, and behavior. However, information regarding host-microbiota interactions is limited in fishes due to their complex living environment. In the present study, an allodiploid hybrid fish derived from herbivorous Megalobrama amblycephala (♀) × carnivorous Culter alburnus (♂) was used to investigate the successional changes of the microbial communities and host-microbiota interactions during herbivorous and carnivorous dietary adaptations. The growth level was not significantly different in any developmental stage between the two diet groups of fish. The diversity and composition of the dominant microbial communities showed similar successional patterns in the early developmental stages, but significantly changed during the two dietary adaptations. A large number of bacterial communities coexisted in all developmental stages, whereas the abundance of some genera associated with metabolism, including Acinetobacter, Gemmobacter, Microbacterium, Vibrio, and Aeromonas, was higher in either diet groups of fish. Moreover, the abundance of phylum Firmicutes, Actinobacteria, and Chloroflexi was positively correlated with the host growth level. In addition, Spearman's correlation analysis revealed that the differentially expressed homologous genes in the intestine associated with cell growth, immunity, and metabolism were related to the dominant gut microbiota. Our results present evidence that host genetics-gut microbiota interactions contribute to dietary adaptation in hybrid fish, which also provides basic data for understanding the diversity of dietary adaptations and evolution in fish.

Relationship of environmental factors in pond water and dynamic changes of gut microbes of sea bass Lateolabrax japonicus

The effect of structure of gut microbes on the health of host has attracted increasing attention. Sea bass Lateolabrax japonicus is an important farmed fish in China. The relationship of the dynamic changes of intestinal bacterial communities in L. japonicus and the cultural water environment is very important for healthy culture. Here, the diversity and abundance of the gut microbial communities of L. japonicus were evaluated during the culture using 16S rRNA Illumina sequencing. Both the opportunistic pathogens Aeromonas (1.68%), Vibrio (1.59%), and Acinetobacter (1.22%); and the potential probiotics Lactobacillus (2.27%), Bacillus (1.16%), and Lactococcus (0.37%) were distributed in the gut of L. japonicus. The increasing concentration of nitrogen of water environments with the increase of culture time significantly correlated with shifts in the microbial community structure: 40.04% of gut microbial changes due to nitrogen concentration. Higher concentrations of nitrogen showed a significantly negative correlation with intestinal probiotics in L. japonicus. The results indicate that the abundance of intestinal bacteria of L. japonicus is mainly driven by the changes of environmental factors (e.g., nitrogen), and it's very important that the linking environmental parameters with bacterial data of guts could be used as an early warning indicator in L. japonicus heath culture.

Rosmarinic acid alone or in combination with Lactobacillus rhamnosus ameliorated ammonia stress in the rainbow trout, Oncorhynchus mykiss: growth, immunity, antioxidant defense and liver functions

Rosmarinic acid (RS) and Lactobacillus rhamnosus (LR) were added singularly or in combination to rainbow trout (Oncorhynchus mykiss) diets to test their efficacy in the protection against ammonia stress. Fish (31.4±0.6 g) were randomly allocated to six groups in three replicates, as follows: T1: basic food as control, T2: LR with a concentration of 1.5 × 108 CFU/g, T3: LR with a concentration of 3 × 108 CFU/g, T4: 1 g RS/kg, T5: 3 g RS/kg, and T6: 1.5 × 108 CFU/g LR + 1 g RS/kg and T7: 3 × 108 CFU/g LR + 3 g RS/kg. After 60 days feeding, fish exposed to 0ammonia stress. After the feeding period, the supplemented fish had the highest final body weight (FW), weight gain (WG), and specific growth rate (SGR), and the lowest feed conversion ratio (FCR) as compared with the control group (P<0.05). Amylase, protease and lipase activities were noticed markedly higher in fish supplemented with 1.5 × 108 CFU/g LR + 1 g RS/kg and 1.5 × 108 CFU/g LR diets compared to the control (P<0.05). Generally, fish in supplemented diets, particularly T2 and T6 groups, had the highest lysozyme, alternative complement activity (ACH50), total Ig, nitroblue tetrazolium test (NBT), myeloperoxidase (MPO), complement component 3 (C3), complement component 4 (C4), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx). On the other hand, T2 and T6 groups had the lowest malondialdehyde (MDA), glucose, and cortisol concentrations as well as alanine aminotransferase (ALT), alkaline phosphatase (ALP), lactate dehydrogenase (LDH) enzyme levels when were compared with the control (P<0.05). After ammonia stress, fish in the supplemented groups, particularly T2 and T6, generally showed significantly higher values of lysozyme, ACH50, total Ig, NBT, MPO, C3, C4, SOD, CAT, GPx and lower levels of MDA, glucose, cortisol, ALT, ALP, LDH when compared with the control (P<0.05). In conclusion, a combined administration of RS and L. rhamnosus effectively improved growth performance and health status as well as enhanced the resistance of rainbow trout against ammonia toxicity.

Isolation of Potential Probiotic Bacillus spp. from the Intestine of Nile Tilapia to Construct Recombinant Probiotic Expressing CC Chemokine and Its Effectiveness on Innate Immune Responses in Nile Tilapia

This study aimed to investigate the potential probiotic Bacillus spp. from the intestine of Nile tilapia in order to construct a recombinant probiotic for the enhancement of the Nile tilapia immune response. One hundred bacterial isolates from the intestine of Nile tilapia were characterized for species identification using the 16s ribosomal RNA (rRNA). Only Bacillus isolates with exhibited antagonistic activity were investigated for their biological functions, which included protease-producing capacity, bile salts and pH tolerance, antibiotic susceptibility, and pathogenicity tests. According to the best results, Bacillus isolate B29, as closely related to B. subtilis, was selected to construct a recombinant probiotic for the delivery of CC chemokine protein (pBESOn-CC). The existence of recombinant probiotics was confirmed by Western blotting before the feeding trial. In addition, the CC chemokine mRNA level was quantified in the intestine of fish fed probiotics after 30 days of feeding. Total immunoglobulin, lysozyme activity, alternative complement 50 activity (ACH50), and phagocytic activity of fish fed either wild-type or recombinant probiotics were significantly increased, indicating that probiotics could stimulate the Nile tilapia immune system through different processes. Interestingly, the dietary supplementation of recombinant probiotics has a stronger immune response enhancement than the wild-type strain.

Growth Performance, Survival, Blood Chemistry, and Immune Gene Expression of Channel Catfish (Ictalurus punctatus) Fed Probiotic-Supplemented Diets

The channel catfish (Ictalurus punctatus) farming industry is the largest and one of the oldest aquaculture industries in the United States. Despite being an established industry, production issues stemming from disease outbreaks remain problematic for producers. Supplementing fish diets with probiotics to enhance the immune system and growth potential is one approach to mitigating disease. Although considerable laboratory data demonstrate efficacy, these results do not always translate to natural modes of disease transmission. Hence, the present work was conducted in the laboratory but incorporated flow-through water from large catfish pond production systems, allowing for natural exposure to pathogens. Two feeding trials were conducted in an 18-tank aquaria system housing two different sizes, 34.8 ± 12.5 g and 0.36 ± 0.03 g, of channel catfish. Channel catfish in the first trial were fed three experimental diets over six weeks. Commercial diets were top-coated with two selected spore-forming Bacillus spp. probiotics, Bacillus velezensis AP193 (1 × 106 CFU g−1) and BiOWiSH (3.6 × 104 CFU g−1), or a basal diet that contained no dietary additive. In the second eight-week trial, diets were top-coated with BiOWiSH at three concentrations (1.8, 3.6, and 7.3 × 104 CFU g−1), along with one basal diet (no probiotic). At the completion of these studies, growth performance, survival, hematocrit, blood chemistry, and immune expression of interleukin 1β (il1β), tumor necrosis factor-alpha (tnf-α), interleukin-8 (il8), transforming-growth factor β1 (tgf-β1), and toll-like receptor 9 (tlr9) were evaluated using qPCR. Trial results revealed no differences (p > 0.05) among treatments concerning growth, survival, or hematological parameters. For immune gene expression, interesting trends were discerned, with substantial downregulation observed in B. velezensis AP193-fed fish for il1β, tnf-α, and tlr9 expression within splenic tissue, compared to that of the basal and BiOWiSH diets (p < 0.05). However, the results were not statistically significant for anterior kidney tissue in the first trial. In the second trial, varied levels of probiotic inclusion revealed no significant impact of BiOWiSH’s products on the expression of il1β, tnf-α, il8, and tgf-β1 in both spleen and kidney tissue at any rate of probiotic inclusion (p > 0.05). Based on these findings, more research on utilizing probiotics in flow-through systems with natural infection conditions is crucial to ensure consistency from a controlled laboratory scale to real-world practices.

Low fish meal diet supplemented with probiotics ameliorates intestinal barrier and immunological function of Macrobrachium rosenbergii via the targeted modulation of gut microbes and derived secondary metabolites

The unsuitable substitution ratio of fish meal by plant protein will reshape the intestinal microbial composition and intestine immunity. However, previous studies were mostly limited to investigating how different feed or probiotics characterized the microbial composition but ignored the biological interactions between bacteria and host physiology through secondary metabolites. Therefore, this study integrates the apparent indicators monitoring, 16S rDNA sequencing, and metabonomics to systematically investigate the effects of cottonseed protein concentrate (CPC) substitution of fish meal and Bacillus coagulans intervention on gut microbes, secondary metabolites, and intestinal immunity of Macrobrachium rosenbergii. Prawns were fed with three diets for 70 days: HF diets contained 25% fish meal, CPC in LF diets were replaced with 10% fish meal, and LF diets supplemented with 2 × 108 CFU/g diet B. coagulans were designated as BC diets. Results showed that CPC substitution induced a significant decrease in digestive enzyme activities (trypsin and lipase) and gut barrier protein PT-1 expression and a significant increase in γ-GT enzyme activity and inflammatory-related factors (Relish and Toll) expression. B. coagulans treatment mitigated the negative changes of the above indicators. Meanwhile, it significantly improved the expression levels of the barrier factor PT-1, the reparative cytokine IL-22, and Cu/Zn-SOD. CPC substitution resulted in a remarkable downregulated abundance of Firmicutes phyla, Flavobacterium spp., and Bacillus spp. B. coagulans treatment induced the callback of Firmicutes abundance and improved the relative abundance of Sphingomonas, Bacillus, and Ralstonia. Functional prediction indicated that CPC substitution resulted in elevated potential pathogenicity of microbial flora, and B. coagulans reduces the pathogenesis risk. Pearson's correlation analysis established a significant positive correlation between differential genera (Sphingomonas, Bacillus, and Ralstonia) and secondary metabolites (including sphingosine, dehydrophytosphingosine, amino acid metabolites, etc.). Meanwhile, the latter were significantly associated with intestinal immunoregulation-related genes (Cu/Zn-SOD, IL-22, PT-1, Toll, and Relish). This study indicated that B. coagulans could mediate specific gut microbes and the combined action of multiple functional secondary metabolites to affect intestinal barrier function, digestion, and inflammation. Our study revealed the decisive role of gut microbes and derived secondary metabolites in the model of dietary composition-induced intestinal injury and probiotic treatment from a new perspective.

Improvement the Hatchery Seed Production Strategy on Embryonic Development and Larval Growth Performance and Development stages of Green Tiger Prawn, Penaeus semisulcatus Using Environmental Aspects

This investigation aimed to improve the hatchery seed production strategy in terms of chronologies of embryonic and larval development as well as hatching, growth and survival rates, and rearing water quality of green tiger prawn, Penaeus semisulcatus by the integration effects of different water temperatures (23 °C, 26 °C, 29 °C, 32 °C) and probiotic as water additives. The best and shortest chronologies of embryonic development stages were in favor of 32 °C with probiotic. The best hatching rate was in favor of 29 °C with probiotics. The fastest larval development and greatest larval growth as total length until PL1 stage was promoted by 32 °C with probiotic but the best survival rate was recorded at 26 °C with probiotic followed by 29 °C with probiotic treatment. During larval development, the lowest value of NH4–N was recorded under the effect of 26 °C and probiotic. Therefore, probiotics as water additives at 29 and 32 °C water temperatures have a beneficial impact on the hatchery seed production strategy and quality of P. semisulcatus. Our findings could apply to rearing larvae in shrimp hatchery to decrease the chronology of embryonic and larval development, while increase the hatching rate, growth performance, and survival rates as well as improving the water quality.

Improvement of aquaculture water quality by mixed Bacillus and its effects on microbial community structure

Microbial remediation, especially the application of probiotics, has recently gained popularity in improving water quality and maintaining aquatic animal health. The efficacy and mechanism of mixed Bacillus for improvement of water quality and its effects on aquatic microbial community structure remain unknown. To elucidate these issues, we applied two groups of mixed Bacillus (Bacillus megaterium and Bacillus subtilis (A0 + BS) and Bacillus megaterium and Bacillus coagulans (A0 + BC)) to the aquaculture system of Crucian carp. Our results showed that the improvement effect of mixed Bacillus A0 + BS on water quality was better than that of A0 + BC, and the NH₄⁺-N, NO₂^--N, NO₃^--N, and total phosphorus (TP) concentrations were reduced by 46.3%, 76.3%, 35.6%, and 80.3%, respectively. In addition, both groups of mixed Bacillus increased the diversity of the bacterial community and decreased the diversity of the fungal community. Microbial community analysis showed that mixed Bacillus A0 + BS increased the relative abundance of bacteria related with nitrogen and phosphorus removal, such as Proteobacteria, Actinobacteria, Comamonas, and Stenotrophomonas, but decreased the relative abundance of pathogenic bacteria (Acinetobacter and Pseudomonas) and fungi (Epicoccum and Fusarium). Redundancy analysis showed that NH₄⁺-N, NO₂^--N, and TP were the primary environmental factors affecting the microbial community in aquaculture water. PICRUST analysis indicated that all functional pathways in the A0 + BS group were richer than those in other groups. These results indicated that mixed Bacillus A0 + BS addition produced good results in reducing nitrogenous and phosphorus compounds and shaped a favorable microbial community structure to further improve water quality.

Synbiotic Lactic Dry® enhanced the growth performance, growth-related genes, intestinal health, and immunity of Nile tilapia reared in inland brackish groundwater

Nile tilapia is recognized as a suitable candidate for intensive farming and sustainability of the aquaculture industry. However, one issue limiting Nile tilapia expansion in arid and semi-arid areas is the scarcity of freshwater resources. In this study, the supplementation of synbiotics was investigated to enhance the growth performance, growth-related genes, intestinal health, and immunity of Nile tilapia reared in inland brackish groundwater. Four diets were prepared where the basal diets were mixed with the dietary mixture of probiotics and prebiotics (Synbiotic Lactic Dry®, a blend of Saccharomyces cerevisiae, Lactobacillus acidophilus, Streptococcus faecium, and Bacillus subtilis, mannan oligosaccharides and β-1.3/1.6-D-glucan) at 0, 0.5, 1, and 2 g/kg. After eight weeks, the final weight and weight gain are linearly increasing with increasing the supplementation level of synbiotic. Markedly fish fed 0.5, 1, and 2 g/kg of synbiotic had higher final weight, weight gain, and feed intake and lower feed conversion ratio (FCR) than fish fed synbiotic free diet. The specific growth rate (SGR) was significantly higher in fish fed 1 and 2 g/kg than in fish fed 0 and 0.5 g/kg. The intestine of fish fed on synbiotic shows an increase in intestinal villi density. Further, the intestine of fish fed on synbiotic showed an increase in the length and branching intestinal villi (anterior, middle, and posterior) in a dose-dependent manner. The lysozyme and phagocytic activities were significantly different from the control, while synbiotic supplementation did not affect the phagocytic index. Interestingly, the results showed marked upregulation of ghrelin, IGF-1, and GH genes in fish fed synbiotics at 0.5, 1, and 2 g/kg. In addition, fish fed 2 g/kg had the highest expression of ghrelin, IGF-1, and GH genes. In conclusion, growing Nile tilapia in inland brackish groundwater can be achieved without negative impacts on the growth performance and health status. Supplementing synbiotics (1-2 g/kg) in Nile tilapia feeds enhanced the growth and feed performances, intestinal histomorphological features, growth-related genes, and immune response.

Effects of a commercial feed additive (Sanacore® GM ) on immune-antioxidant profile and resistance of gilthead seabream (Sparus aurata) against Vibrio alginolyticus infection

The effects of a functional additive (Sanacore® GM; SAN ) on immune and antioxidant indices, and the resistance of gilthead seabream (Sparus aurata) against Vibrio alginolyticus infection. For this, four diets containing 0% (the control), 0.1%, 0.2%, and 0.4% SAN were offered to triplicated groups of fish (20 - 23 g) for ten weeks. Subsequently, fish were injected intraperitoneally with V. alginolyticus and monitored for further ten days. Feeding the fish on SAN-supplemented diets showed positive effects on leukocyte counts and its differential percentages. Serum lysozyme activity and total immunoglobulin values, as well as phagocytic activity and indices, were linearly and quadratically higher in SAN-fed fish; especially at the 0.4% SAN diet. Similarly, linear and quadratic increases in catalase, superoxide dismutase, and total antioxidant capacity were observed in SAN-fed fish, particularly at the 0.4% SAN diet. Conversely, serum malondialdehyde values decreased in SAN-fed fish compared with the control group, which showed its highest value. The highest expression of the IL-1β gene coupled with the lowest TNF-α and HSP70 genes expressions was found in the fish fed with the 0.4% SAN. On the other hand, fish fed on the control diet showed the lowest IL-1β gene coupled with the highest TNF-α and HSP70 genes expressions. After bacterial infection, most of the control fish died with a relative percent of survival of 5.0%; meanwhile feeding gilthead seabream on SAN-enriched diets significantly enhanced their protection against V. alginolyticus infection. Fish fed on the 0.4% SAN diet showed 100% survival. The SAN administration to gilthead seabream especially at the 0.4% level led to significant promotions in antioxidative and immune responses and augment the fish resistance to V. alginolyticus infection.

Use of Probiotic Bacteria and Bacteriocins as an Alternative to Antibiotics in Aquaculture

In addition to their use in human medicine, antimicrobials are also used in food animals and aquaculture, and their use can be categorized as therapeutic against bacterial infections. The use of antimicrobials in aquaculture may involve a broad environmental application that affects a wide variety of bacteria, promoting the spread of bacterial resistance genes. Probiotics and bacteriocins, antimicrobial peptides produced by some types of lactic acid bacteria (LAB), have been successfully tested in aquatic animals as alternatives to control bacterial infections. Supplementation might have beneficial impacts on the intestinal microbiota, immune response, development, and/or weight gain, without the issues associated with antibiotic use. Thus, probiotics and bacteriocins represent feasible alternatives to antibiotics. Here, we provide an update with respect to the relevance of aquaculture in the animal protein production sector, as well as the present and future challenges generated by outbreaks and antimicrobial resistance, while highlighting the potential role of probiotics and bacteriocins to address these challenges. In addition, we conducted data analysis using a simple linear regression model to determine whether a linear relationship exists between probiotic dose added to feed and three variables of interest selected, including specific growth rate, feed conversion ratio, and lysozyme activity.

Impact of Putative Probiotics on Growth, Behavior, and the Gut Microbiome of Farmed Arctic Char (Salvelinus alpinus)

Beneficial bacteria promise to promote the health and productivity of farmed fish species. However, the impact on host physiology is largely strain-dependent, and studies on Arctic char (Salvelinus alpinus), a commercially farmed salmonid species, are lacking. In this study, 10 candidate probiotic strains were subjected to in vitro assays, small-scale growth trials, and behavioral analysis with juvenile Arctic char to examine the impact of probiotic supplementation on fish growth, behavior and the gut microbiome. Most strains showed high tolerance to gastric juice and fish bile acid, as well as high auto-aggregation activity, which are important probiotic characteristics. However, they neither markedly altered the core gut microbiome, which was dominated by three bacterial species, nor detectably colonized the gut environment after the 4-week probiotic treatment. Despite a lack of long-term colonization, the presence of the bacterial strains showed either beneficial or detrimental effects on the host through growth rate enhancement or reduction, as well as changes in fish motility under confinement. This study offers insights into the effect of bacterial strains on a salmonid host and highlights three strains, Carnobacterium divergens V41, Pediococcus acidilactici ASG16, and Lactiplantibacillus plantarum ISCAR-07436, for future research into growth promotion of salmonid fish through probiotic supplementation.

Effects of probiotics on Zebrafish model infected with Aeromonas hydrophila: spatial distribution, antimicrobial, and histopathological investigation

Usage of “probiotics” for treatment of food-borne pathogens associated diseases, makes a significant reduction in transmission of resistant bacteria, and antimicrobial resistance genes from aquaculture environments to humans. In this research, the authors aim to evaluate the immunomodulatory, and histological effects of two probiotic strains on the Zebrafish model. Fish models were treated with Lactobacillus delbrueckii (G2), Lactobacillus acidophilus (G3) and both probiotics (G4) and compared with the control group (G1) (only infected by pathogen and receiving no probiotic). Biometric tests, height, weight, and mortality rate of the fishes were assessed. Afterward, RT-PCR was conducted for bacterial existence of probiotic strains, and quantitative assessment of alterations in targeted immune genes. Subsequently, histological sampling was done for investigation of spatial distribution, and villus length in proximal, middle, and distal sections of intestinal tissues. Based on the results, G4 showed the highest gene expression for Lactobacillus acidophilus after 28 days (P < 0.05). G4 also showed an increase in the number of goblet cells and villus length in the middle and distal sections of intestinal tissue after 56 days. Furthermore, after 56 days, the highest number of intraepithelial cells was observed in the proximal sections of intestinal tissue in G4. G2 and G3 showed significant differences in comparison with G1 (P < 0.05). After 60 days, the highest gene expression for Lactobacillus bulgaricus was found in group treated with only this probiotic bacteria. The highest expression level of IL-1β and TNF-α were found in G1. The highest survival rate was in the case of groups only treated with Lactobacillus bulgaricus (G2). To sum up, it seems that usage of probiotics for the improvement of public health and fisheries industries can be helpful.

Efficiency of a probiotic in carp lactococcosis in an in vitro experiment

The purpose of this article is to study the effect of the probiotic on experimental infections of carp's fingerlings with Lactococcus garvieae. Lactic acid bacteria (LAB) (Lactobacillus fermentum 24с, Pediococcus pentosaceus 10/9к, Lactobacillus paracasei 9c) for the probiotic were previously isolated from the intestines of mature carps from Maybalyk commercial fisheries, which provided fingerlings for this experiment too as well. The feed-contained probiotic was given to fish in the experimental group for 14 days before challenge with pathogen L. garvieae. Throughout ten days after the infection, death of the fish was regularly recorded in the group, where the probiotic was not given with the feeding. Ten days after, all fish in this group died. In the probiotic group, the mortality on the tenth day after the challenge with pathogen was 10%. It was concluded the effect of the probiotic is not due to antibacterial action to the pathogen. The effectiveness of the probiotic can be associated with the displacement of the pathogen, due to the competitive adhesion and/or more likely, with the activation of the immune response from the fish organism due to the addition of the probiotic to the feed.

Dietary lipid levels affected antioxidative status, inflammation response, apoptosis and microbial community in the intestine of juvenile turbot (Scophthalmus maximus L.)

A nine-week feeding trial was conducted to comprehensively investigate the effects of different levels of dietary lipid on intestinal physiology of juvenile turbot. Three diets with different lipid levels (8%, 12% and 16%) were formulated, which were designated as the low-lipid group (LL), medium-lipid group (ML) and high-lipid group (HL), respectively. Each diet was fed to six replicate tanks, and each tank was stocked with 35 fish. The results revealed that medium dietary lipid (12%) increased the activities of intestinal digestive enzymes and brush border enzymes. Excessive dietary lipid (16%) decreased the intestinal antioxidative enzyme levels and increased the lipid peroxidation pressure. In addition, HL stimulated the occurrence of intestinal inflammation and significantly up-regulated the mRNA expression level of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interferon-γ (IFN-γ) and transforming growth factor-β (TGF-β). Dietary LL and HL induced the apoptosis of intestinal epithelial cells. Sequencing of bacterial 16 s rRNA V4 region indicated that the abundance and diversity of intestinal microflora in fish fed with medium lipid diet (12%) were significantly higher than those in other groups, indicating the intestinal microflora ecology in group ML was more balanced. MetaStat analysis indicated that both low- and high-lipid diets significantly reduced the relative abundance of intestinal beneficial bacteria. In conclusion, results of this study demonstrated the sensitivity of intestinal health and microbiota to dietary lipid levels. From the perspective of microecological balance, medium dietary lipid (12%) was more conducive to maintaining the intestinal microflora stability of turbot.

Combined and Singular Effects of Ethanolic Extract of Persian Shallot (Allium hirtifolium Boiss) and Synbiotic Biomin®IMBO on Growth Performance, Serum- and Mucus-Immune Parameters and Antioxidant Defense in Zebrafish (Danio rerio)

Simple Summary

The present study investigated the effect of combined and singular ethanolic extract of Persian shallot and synbiotic Bomin^®IMBO in zebrafish. The aim of this study is to measure a range of parameters consisting of growth performance, serum and mucus immune parameters, and antioxidant defense. The results indicated that the measured parameters have a positive effect and hence we can suggest administration of these additives in zebrafish culture.

Abstract

This study was carried out to evaluate combined and singular effects of ethanolic extract of Persian shallot (Allium hirtifolium Boiss) and synbiotic Biomin^®IMBO on growth performance, innate immune responses, and antioxidant defense in zebrafish (Danio rerio). Fish with initial weight of 151.90 ± 0.31 mg were allocated in 21 10-L glass aquariums. The experimental groups were as follows: T1, control (without any supplementation); T2, 1% synbiotic; T3, 3% synbiotic; T4, 1% Persian shallot (as a medical plant); T5, 3% Persian shallot; T6, 1% Persian shallot and 1% synbiotic; T7, 3% Persian shallot and 3% synbiotic. At the end of the experiment (60 days), all treatments significantly showed higher final weight (FW), weight gain (WG), WG (%), and specific growth rate (SGR) compared with the fish fed on control diet. Furthermore, both synbiotic Biomin^®IMBO and Persian shallot significantly improved intestine immune parameters including lysozyme, alternative complement hemolytic activity (ACH50), total immunoglobulin (total Ig), and myeloperoxidase (MPO) of zebrafish compared to fish fed on control diet (p < 0.05). Also, in all experimental groups, hepatic catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione reductase (GR) activities significantly increased compared to the control group. Whereas, the highest MDA level was observed in the control group compared to the treatments (p < 0.05). Moreover, skin mucus immune parameters of zebrafish have been noticeably improved with synbiotic Biomin^®IMBO and Persian shallot compared to fish fed on the control diet (p < 0.05). The results indicate that synbiotic or Persian shallot supplemented diet could enhance the general health status of the zebrafish.

Nanoplastics Induce More Serious Microbiota Dysbiosis and Inflammation in the Gut of Adult Zebrafish than Microplastics

Microplastics (MPs) (< 5 mm) and nanoplastics (NPs) (< 100 nm) are emerging environmental pollutants and have been proved could cause a series of toxicity in aquatic organisms. In this study, the effects on gut microbiota of adult zebrafish exposed for 21 days to 10 μg/L and 1 mg/L of MPs (8 μm) and NPs (80 nm) were evaluated. We analyzed the intestinal microbial community of zebrafish using high throughput sequencing of the 16S rRNA gene V3-V4 region and also performed transcriptional profiling of the inflammation pathway related genes in the intestinal tissues. Our results showed that both spherical polystyrene MPs and NPs could induce microbiota dysbiosis in the gut of zebrafish. The flora diversity of gut microbiota significantly increased under a high concentration of NPs. At the phylum level, the abundance of Proteobacteria increased significantly and the abundance of Fusobacteria, Firmicutes and Verrucomicrobiota decreased significantly in the gut after 21-day exposure to 1 mg/L of both MPs and NPs. Furthermore, interestingly, the abundance of Actinobacteria decreased in the MPs treatment groups but increased in the NPs treatment groups. At the genus level, revealed that the relative abundance of Aeromonas significantly increased both in the MPs and NPs treatment groups. Moreover, it was observed that NPs increased mRNA levels of il8, il10, il1β and tnfα in the gut, but not in MPs exposure group, indicating that the NPs may have a more serious effect on the gut of zebrafish than MPs to induce microbiota dysbiosis and inflammation in the gut.

Dietary supplementation of Bacillus velezensis B8 enhances immune response and resistance against Aeromonas veronii in grass carp

The heavy use of prophylactic antibiotics in aquaculture leads to elevated antibiotic residues, posing a huge hidden danger in aquaculture products and other natural aquatic environments. Therefore, this study aims to isolate probiotics that can replace antibiotics from the gut of grass carp for disease control. Bacillus velezensis B8 was isolated from the gut of grass carp and showed broad-spectrum antimicrobial activity against several fish pathogenic bacteria, including Aeromonas hydrophilis, Aeromonas veronii, Vibrio parahaemolyticus, Escherichia coli, Edwardsiella tarda and Vibrio mimicus. The safety evaluation showed that the strain B8 was non-toxic to grass carp, had no hemolytic activity, and was sensitive to most antibiotics. In vitro study indicated that strain B8 was viable at pH 2-7, had weak tolerance to 0.1% (w/v) bile salt, and could grow at 10°C-40 °C. The grass carps were fed with diets containing 0 (control), 10⁷, and 10⁹ cfu/g of strain B8 for 4 weeks. Various immune parameters were measured at 1, 2, 3, and 4 weeks of post-feeding. The results of non-specific immunoassay showed that diets supplemented with B8 significantly increased alkaline phosphatase (AKP) and superoxide dismutase (SOD) activity in serum samples (p < 0.05). The expression levels of immune-related genes in the kidney and spleen of grass carp were measured. Among them, the expression levels of IgM and TNF-α both in spleen and kidney were significantly increased after 3 and 4 weeks of post-feeding (p < 0.05). The expression of IgD and MHCI in kidney was significantly upregulated in high-dose groups after 2 and 3 weeks of feeding, respectively (p < 0.05). In addition, after 7 days of challenging with A. veronii, the high-dose group and low-dose group had 48% and 53% survival compared to 25% survival for the control group. These results suggest that B. velezensis B8 has the potential to be developed into a microecological preparation for the alternatives of antibiotics in aquaculture.

Exploring the garlic (Allium sativum) properties for fish aquaculture

The aquaculture industry's rapid growth to meet commercial demand can trigger an outbreak of infectious diseases due to high-density farming. Antibiotic overuse and misuse in fish farming and its global health consequences have led to searching for more natural alternatives such as medicinal plants. In this sense, garlic (Allium sativum) has different bioactive compounds with biological properties for animal health. Among them are the ajoene, alliin, and allicin, which confer biological properties such as growth promotion, antimicrobial, antiviral, antioxidant, and antiparasitic. Ways to use garlic in aquaculture include oil, fresh mash, aqueous extract, and garlic powder. The powder presentation is the most used in aquaculture; it is generally applied by oral administration, adding to the feed, and the dose used ranges from 0.05 to 40 g/kg of feed. Garlic has been used in the aquaculture of different species such as rainbow trout (Oncorhynchus mykiss), spotted grouper (Epinephelus coioides), catfish (Clarias gariepinus), tilapia (Oreochromis niloticus), guppy fish (Poecilia reticulata), goldfish (Carassius auratus), and barramundi (Lates calcarifer). In addition to its properties, garlic's usage became popular, thanks to its low cost, easy incorporation into food, and little environmental impact. Therefore, its application can be an effective solution to combat diseases, improve organisms' health using natural supplies, and as an alternative to antibiotics. This review reports and discusses plant-derived products' beneficial properties, emphasizing garlic and its usages in fish aquaculture.

Mixed culture of Bacillus aerius B81e and Lactiplantibacillus paraplantarum L34b-2 derived from in vivo screening using hybrid catfish exhibits high probiotic effects on Pangasius bocourti

A mixed culture of probiotics, one from the genus Bacillus and one lactic acid bacterium (LAB), was developed to be used as a feed additive for enhancing growth, innate immunity and disease resistance in Pangasius bocourti. From our earlier work, three probiotic Bacillus species, Bacillus siamensis B44v, Bacillus sp. B51f and Bacillus aerius B81e, and three probiotic LABs, Streptococcus lutetiensis L7c, Lactiplantibacillus paraplantarum (synonym. Lactobacillus paraplantarum) L34b-2 and Lactiplantibacillus plantarum (synonym. Lactobacillus plantarum) L42g, were selected for comparison. These bacteria, which express probiotic properties including bacteriocin-like activity against Aeromonas hydrophila, were subjected to in vivo screening in hybrid catfish (Clarias macrocephalus × Clarias gariepinus). A 30-day feed-trial followed by a challenge test in screening experiments resulted in the prominent B. aerius B81e and L. paraplantarum L34b-2 being selected. A mixture of these bacteria was added to a diet for P. bocourti. After 60-day feeding, the fish fed with mixed probiotics had weight gain, specific growth rate and feed conversion ratio improved significantly (p < 0.01) when compared to the control. Both humoral and cellular immunity were significantly higher in probiotic-fed fish. Following the 60-day feeding experiment, P. bocourti fed with the diet containing mixed probiotics had a higher survival rate than the control fish after injection with a virulent A. hydrophila. It can be concluded that a combination of B. aerius strain B81e and L. paraplantarum strain L34b-2 markedly improved growth performance, innate immunity and disease resistance of P. bocourti.

Screening of New Potential Probiotics Strains against Photobacterium damselae Subsp. piscicida for Marine Aquaculture

On intensive fish farms, 10% of the population dies exclusively from pathogens, and Photobacterium damselae subsp. Piscicida (Ph. damselae subsp. Piscicida), the bacteria causing pasteurellosis in marine aquaculture, is one of the major pathogens involved. The objective of this study was to obtain new probiotic strains against pasteurellosis in order to limit the use of chemotherapy, avoiding the environmental repercussions generated by the abusive use of these products. In this study, 122 strains were isolated from the gills and intestines of different marine fish species and were later evaluated in vitro to demonstrate the production of antagonistic effects, the production of antibacterial substances, adhesion and growth to mucus, resistance to bile and resistance to pH gradients, as well as its harmlessness and the dynamic of expression of immune-related genes by real-time PCR after administration of the potential probiotic in the fish diet. Only 1/122 strains showed excellent results to be considered as a potential probiotic strain and continue its characterization against Ph. damselae subsp. piscicida to determine its protective effect and elucidating in future studies its use as a possible probiotic strain for marine aquaculture.

Effect of in Ovo Inoculation of Bifidobacterium spp. on Growth Performance, Thyroid Activity, Ileum Histomorphometry, and Microbial Enumeration of Broilers

Early colonization by beneficial bacteria stimulates the function and development of the digestive tract, on which the performance and vitality of broilers rely. This experiment evaluated the effects of in ovo injection of bifidobacteria on the performance, thyroid activity, bacterial enumeration, and ileal histomorphometry of broiler chickens. A total of 360 fertile eggs were inoculated into the yolk sac, on day 17 of embryogenesis, and allocated to six experimental groups: negative control (not injected, G1), positive control (injected with sterilized distilled water, G2), and groups inoculated with 2 × 10⁸ CFU of Bifidobacterium bifidum, G3; B. animalis, G4; B. longum, G5; or B. infantis, G6. The results revealed an increase (P < 0.01) in body weight and weight gain in all treated groups increases of at least 5.38 and 8.27%, respectively, compared with the control. Feed consumption was not affected during all experimental periods, while the feed conversion ratio (FCR) was enhanced (P < 0.01) only for the overall experimental period (1-28 days of age). The G3 birds recorded the lowest FCR (1.38), while the highest was observed in G1 birds (1.57). Serum concentrations of thyroxin and triiodothyronine were elevated (P < 0.05) with probiotic inoculation. The antioxidant status and immune response of bifidobacteria injected birds were improved; the serum contents of superoxide dismutase and immunoglobulins Y, M, and A were increased (P < 0.05 and P < 0.01), while the malondialdehyde content was decreased (P < 0.01). Ileal architecture was improved in the bifidobacteria treated groups; the highest values of villus height and the villus height/crypt depth ratio were recorded in G3 (936.6 and 11.80) compared with those of G1 (537.1 and 6.93). Moreover, ileal lactic acid bacteria and Bifidobacterium spp. counts increased by at least 10.64 and 51.75%, while total coliform and bacterial counts reduced by at least 15.46 and 15.18%, respectively, compared with those of the control. In conclusion, all tested strains of bifidobacteria enhanced broiler growth performance, ileal function, and thyroid hormone metabolism without obvious differences among them.

Probiotics-Live Biotherapeutics: a Story of Success, Limitations, and Future Prospects-Not Only for Humans

In livestock production, lactic acid bacteria (LAB) represent the most widespread microorganisms used as probiotics. For such critical use, these bacteria must be correctly identified and characterized to ensure their safety and efficiency. Recently, probiotics have become highly recognized as supplements for humans and in particular for animals because of their beneficial outcome on health improvement and well-being maintenance. Various factors, encompassing dietary and management constraints, have been demonstrated to tremendously influence the structure, composition, and activities of gut microbial communities in farm animals. Previous investigations reported the potential of probiotics in animal diets and nutrition. But a high rate of inconsistency in the efficiency of probiotics has been reported. This may be due, in a major part, to the dynamics of the gastrointestinal microbial communities. Under stressing surroundings, the direct-fed microbials may play a key role as the salient limiting factor of the severity of the dysbiosis caused by disruption of the normal intestinal balance. Probiotics are live microorganisms, which confer health benefits on the host by positively modifying the intestinal microflora. Thus, the aim of this review is to summarize and to highlight the positive influence of probiotics and potential probiotic microbe supplementation in animal feed with mention of several limitations.

Probiotic Bacteria with High Alpha-Gal Content Protect Zebrafish against Mycobacteriosis

Mycobacteriosis affects wild fish and aquaculture worldwide, and alternatives to antibiotics are needed for an effective and environmentally sound control of infectious diseases. Probiotics have shown beneficial effects on fish growth, nutrient metabolism, immune responses, disease prevention and control, and gut microbiota with higher water quality. However, the identification and characterization of the molecules and mechanisms associated with probiotics is a challenge that requires investigation. To address this challenge, herein we used the zebrafish model for the study of the efficacy and mechanisms of probiotic interventions against tuberculosis. First, bacteria from fish gut microbiota were identified with high content of the surface glycotope Galα1-3Galβ1-(3)4GlcNAc-R (α-Gal) that has been shown to induce protective immune responses. The results showed that probiotics of selected bacteria with high α-Gal content, namely Aeromonas veronii and Pseudomonas entomophila, were biosafe and effective for the control of Mycobacterium marinum. Protective mechanisms regulating immunity and metabolism activated in response to α-Gal and probiotics with high α-Gal content included modification of gut microbiota composition, B-cell maturation, anti-α-Gal antibodies-mediated control of mycobacteria, induced innate immune responses, beneficial effects on nutrient metabolism and reduced oxidative stress. These results support the potential of probiotics with high -Gal content for the control of fish mycobacteriosis and suggested the possibility of exploring the development of combined probiotic treatments alone and in combination with -Gal for the control of infectious diseases.

Mechanisms Used by Probiotics to Confer Pathogen Resistance to Teleost Fish

Probiotics have been defined as live microorganisms that when administered in adequate amounts confer health benefits to the host. The use of probiotics in aquaculture is an attractive bio-friendly method to decrease the impact of infectious diseases, but is still not an extended practice. Although many studies have investigated the systemic and mucosal immunological effects of probiotics, not all of them have established whether they were actually capable of increasing resistance to different types of pathogens, being this the outmost desired goal. In this sense, in the current paper, we have summarized those experiments in which probiotics were shown to provide increased resistance against bacterial, viral or parasitic pathogens. Additionally, we have reviewed what is known for fish probiotics regarding the mechanisms through which they exert positive effects on pathogen resistance, including direct actions on the pathogen, as well as positive effects on the host.

Effects of phytonutrient-supplemented diets on the intestinal microbiota of Cyprinus carpio

In the aquaculture sector, a strategy for the more efficient use of resources and proper disease control is needed to overcome the challenges of meat production worldwide. Modulation of the gastrointestinal tract microbiota is a promising approach for promoting animal health and preventing infection. This feeding experiment was conducted to discover the phytonutrient-induced changes in the gastrointestinal tract microbiota of common carp (Cyprinus carpio). Acclimatized animals aged 7 months (30 weeks) were divided randomly into five experimental groups to investigate the effects of the applied feed additives. The dietary supplements were manufactured from anthocyanin-containing processing wastes from the food industry, specifically the production of Hungarian sour cherry extract, synbiotics from fermented corn, and fermentable oligosaccharides from Hungarian sweet red pepper seeds and carotenoids from Hungarian sweet red pepper pulps, applied at a dose of 1%. The gut contents of the animals were collected at four time points throughout the 6-week study period. To track the compositional and diversity changes in the microbiota of the carp intestinal tract, V3-V4 16S rRNA gene-based metagenomic sequencing was performed. The growth performance of common carp juveniles was not significantly affected by supplementation of the basal diet with plant extracts. Phytonutrients improve the community diversity, increase the Clostridium and Lactobacillus abundances and decrease the abundances of potentially pathogenic and spoilage bacteria, such as Shewanella, Pseudomonas, Acinetobacter and Aeromonas. The phyla Proteobacteria, Tenericutes and Chlamydiae were positively correlated with the body weight, whereas Spirochaetes and Firmicutes exhibited negatively correlations with the body weight. We hypothesize that the application of phytonutrients in aquaculture settings might be a reasonable green approach for easing the usage of antibiotics.

Isolation and Characterization of a Bacillus velezensis D-18 Strain, as a Potential Probiotic in European Seabass Aquaculture

Within the food-producing sectors, aquaculture is the one that has developed the greatest growth in recent decades, currently representing almost 50% of the world's edible fish. The diseases can affect the final production in intensive aquaculture; in seabass, aquaculture vibriosis is one of the most important diseases producing huge economical losses in this industry. The usual methodology to solve the problems associated with the bacterial pathology has been the use of antibiotics, with known environmental consequences. This is why probiotic bacteria are proposed as an alternative fight against pathogenic bacteria. The aim of this study was to analyse a strain of Bacillus velezensis D-18 isolated from a wastewater sample collected from a fish farm, for use as probiotics in aquaculture. The strain was evaluated in vitro through various mechanisms of selection, obtaining as results for growth inhibition by co-culture a reduction of 30%; B. velezensis D-18 was able to survive at 1.5-h exposure to 10% seabass bile, and at pH 4, its survival is 5% and reducing by 60% the adhesion capacity of V. anguillarum 507 to the mucus of seabass and in vivo by performing a challenge. Therefore, in conclusion, we consider B. velezensis D-18 isolate from wastewater samples collected from the farms as a good candidate probiotic in the prevention of the infection by Vibrio anguillarum 507 in European seabass after in vitro and biosafety assays.

Isolation and Characterization of Fish-Gut Bacillus spp. as Source of Natural Antimicrobial Compounds to Fight Aquaculture Bacterial Diseases

Aquaculture is responsible for more than 50% of global seafood consumption. Bacterial diseases are a major constraint to this sector and associated with misuse of antibiotics, pose serious threats to public health. Fish-symbionts, co-inhabitants of fish pathogens, might be a promising source of natural antimicrobial compounds (NACs) alternative to antibiotics, limiting bacterial diseases occurrence in aquafarms. In particular, sporeforming Bacillus spp. are known for their probiotic potential and production of NACs antagonistic of bacterial pathogens and are abundant in aquaculture fish guts. Harnessing the fish-gut microbial community potential, 172 sporeforming strains producing NACs were isolated from economically important aquaculture fish species, namely European seabass, gilthead seabream, and white seabream. We demonstrated that they possess anti-growth, anti-biofilm, or anti-quorum-sensing activities, to control bacterial infections and 52% of these isolates effectively antagonized important fish pathogens, including Aeromonas hydrophila, A. salmonicida, A. bivalvium, A. veronii, Vibrio anguillarum, V. harveyi, V. parahaemolyticus, V. vulnificus, Photobacterium damselae, Tenacibaculum maritimum, Edwardsiela tarda, and Shigella sonnei. By in vitro quantification of sporeformers' capacity to suppress growth and biofilm formation of fish pathogens, and by assessing their potential to interfere with pathogens communication, we identified three promising candidates to become probiotics or source of bioactive molecules to be used in aquaculture against bacterial aquaculture diseases.

Gnotobiotic rainbow trout (Oncorhynchus mykiss) model reveals endogenous bacteria that protect against Flavobacterium columnare infection

The health and environmental risks associated with antibiotic use in aquaculture have promoted bacterial probiotics as an alternative approach to control fish infections in vulnerable larval and juvenile stages. However, evidence-based identification of probiotics is often hindered by the complexity of bacteria-host interactions and host variability in microbiologically uncontrolled conditions. While these difficulties can be partially resolved using gnotobiotic models harboring no or reduced microbiota, most host-microbe interaction studies are carried out in animal models with little relevance for fish farming. Here we studied host-microbiota-pathogen interactions in a germ-free and gnotobiotic model of rainbow trout (Oncorhynchus mykiss), one of the most widely cultured salmonids. We demonstrated that germ-free larvae raised in sterile conditions displayed no significant difference in growth after 35 days compared to conventionally-raised larvae, but were extremely sensitive to infection by Flavobacterium columnare, a common freshwater fish pathogen causing major economic losses worldwide. Furthermore, re-conventionalization with 11 culturable species from the conventional trout microbiota conferred resistance to F. columnare infection. Using mono-re-conventionalized germ-free trout, we identified that this protection is determined by a commensal Flavobacterium strain displaying antibacterial activity against F. columnare. Finally, we demonstrated that use of gnotobiotic trout is a suitable approach for the identification of both endogenous and exogenous probiotic bacterial strains protecting teleostean hosts against F. columnare. This study therefore establishes an ecologically-relevant gnotobiotic model for the study of host-pathogen interactions and colonization resistance in farmed fish.

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.

Advances in Microbiome Research for Animal Health

Host-associated microbiomes contribute in many ways to the homeostasis of the metaorganism. The microbiome's contributions range from helping to provide nutrition and aiding growth, development, and behavior to protecting against pathogens and toxic compounds. Here we summarize the current knowledge of the diversity and importance of the microbiome to animals, using representative examples of wild and domesticated species. We demonstrate how the beneficial ecological roles of animal-associated microbiomes can be generally grouped into well-defined main categories and how microbe-based alternative treatments can be applied to mitigate problems for both economic and conservation purposes and to provide crucial knowledge about host-microbiota symbiotic interactions. We suggest a Customized Combination of Microbial-Based Therapies to promote animal health and contribute to the practice of sustainable husbandry. We also discuss the ecological connections and threats associated with animal biodiversity loss, microorganism extinction, and emerging diseases, such as the COVID-19 pandemic.