Probiotic bacteria as biological control agents in aquaculture

Polyamide microplastics can mitigate the effects of pathogenic bacterium on the health of marine mussels

Vibrio parahaemolyticus and microplastics are prevalent in the ocean. Bacteria attach onto plastic particles, forming harmful biofilms that collectively threaten bivalve health. This study investigates the interaction between polyamide microplastics (PA: particle size 38 ± 12 µm) and V. parahaemolyticus, as well as their combined impact on thick-shelled mussels (Mytilus coruscus). We introduced 1011 CFU/L of V. parahaemolyticus into varying PA concentrations (0, 5, 50, and 500 particles/L) to observe growth over 14 h and biofilm formation after 48 h. Our findings indicate that microplastics suppress biofilm formation and virulence gene expression. Four treatments were established to monitor mussel responses: a control group without PA or V. parahaemolyticus; a group with 50 particles/L PA; a group with 1011 CFU/L V. parahaemolyticus; and a co-exposure group with both 50 particles/L PA and 1011 CFU/L V. parahaemolyticus, over a 14-day experiment. However, combined stress from microplastics and Vibrio led to immune dysregulation in mussels, resulting in intestinal damage and microbiome disruption. Notably, V. parahaemolyticus had a more severe impact on mussels than microplastics alone, yet their coexistence reduced some harmful effects. This study is the first to explore the interaction between microplastics and V. parahaemolyticus, providing important insights for ecological risk assessments.

The Application of Fungi and Their Secondary Metabolites in Aquaculture

Ensuring sustainability has increasingly become a significant concern not only in aquaculture but in the general agrifood sector. Therefore, it is imperative to investigate pathways to feed substitutes/best practices to enhance aquaculture sustainability. The application of fungi in aquaculture provides innovative methods to enhance the sustainability and productivity of aquaculture. Fungi play numerous roles in aquaculture, including growth, immunity enhancement and disease resistance. They also play a role in bioremediation of waste and bioflocculation. The application of fungi improves the suitability and utilization of terrestrial plant ingredients in aquaculture by reducing the fibre fractions and anti-nutritional factors and increasing the nutrients and mineral contents of plant ingredients. Fungi are good flotation agents and can enhance the buoyancy of aquafeed. Pigments from fungi enhance the colouration of fish fillets, making them more attractive to consumers. This paper, via the relevant literature, explores the multifaceted roles of fungi in aquaculture, emphasizing their potential to transform aquaculture through environmentally friendly and sustainable techniques. The effectiveness of fungi in reducing fibre fractions and enhancing nutrient availability is influenced by the duration of fermentation and the dosage administered, which may differ for various feed ingredients, making it difficult for most aquaculture farmers to apply fungi approximately. Therefore, the most effective dosage and fermentation duration for each feed ingredient should be investigated.

The mitigating effects and mechanisms of Bacillus cereus on chronic cadmium poisoning in Litopenaeus vannamei based on histopathological, transcriptomic, and metabolomic analyses

Shrimp are non-negligible victims of cadmium (Cd) contamination, and there is still a lack of strategies for mitigating Cd toxicity in shrimp. Bacillus cereus, with its significant heavy metal (HM) tolerance and chelating effects, is a representative beneficial bacterium to be investigated for mitigating the toxicity of Cd exposure. This study revealed the effects and potential mechanisms of B. cereus in mitigating chronic Cd toxicity in shrimp by analyzing growth performance, hepatopancreatic Cd accumulation, pathology, as well as comprehensive hepatopancreatic transcriptomics and metabolomics in Litopenaeus vannamei. The results showed that shrimp's growth inhibition, hepatopancreatic Cd accumulation and physiological structure damage in B. cereus+chronic Cd group were effectively alleviated compared with the chronic Cd treatment group. The pathways related to amino acid metabolism, glycolipid metabolism, immune response, and antioxidant stress were significantly activated in the B. cereus+chronic Cd group, including glycolysis, pentose phosphate pathway, oxidative phosphorylation, biosynthesis of amino acids, and biosynthesis of unsaturated fatty acids pathways. The key differentially expressed genes (e.g., macrophage migration inhibitory factor, glycine cleavage system H protein, glycine dehydrogenase, phosphoglucomutase-2, asparaginase, ATP synthase subunit, cytochrome c, and 4-hydroxyphenylpyruvate dioxygenase) and metabolites (e.g., L-leucine, D-ribose, gluconic acid, 6-Phosphogluconic acid, sedoheptulose 7-phosphate, 1-Kestose, glyceric acid, arachidic acid, prostaglandins, 12-Keto-tetrahydro-leukotriene B4, and gamma-glutamylcysteine) associated with the above pathways were significantly altered. This study demonstrated that B. cereus is an effective mitigator for the treatment of chronic Cd poisoning in shrimp. B. cereus may play a role in alleviating the toxicity of Cd by enhancing the antioxidant performance, immune defense ability, metabolic stability, and energy demand regulation of shrimp. The study provides reference materials for the study of B. cereus in alleviating Cd toxicity of shrimp and broadens the application of probiotics in treating HM toxicity.

Serodiversity, antibiotic resistance, and virulence genes of Vibrio parahaemolyticus in oysters collected in coastal areas of northwestern Mexico between 2012 and 2020

This study aimed to determine the prevalence of V. parahaemolyticus in oysters from the northwestern coast of Mexico and to identify the serotypes, virulence factors, and antibiotic resistance of the strains. Oyster samples were collected from 2012 to 2020 from the northwest coast of Mexico; biochemical and molecular methods were used to identify V. parahaemolyticus from oysters; antiserum reaction to determine V. parahaemolyticus serotypes, and PCR assays were performed to identify pathogenic (tdh and/or trh) or pandemic (toxRS/new, and/or orf8) strains and antibiotic resistance testing. A total of 441 oyster samples were collected and tested for V. parahaemolyticus. Forty-seven percent of oyster samples were positive for V. parahaemolyticus. Ten different O serogroups and 72 serovars were identified, predominantly serotype O1:KUT with 22.2% and OUT:KUT with 17.3%. Twenty new serotypes that had not been previously reported in our region were identified. We detected 4.3% of pathogenic clones but no pandemic strains. About 73.5% of strains were resistant to at least one antibiotic, mainly ampicillin and ciprofloxacin; 25% were multi-drug resistant. In conclusion, the pathogenic strains in oysters and antibiotic resistance are of public health concern, as the potential for outbreaks throughout northwestern Mexico is well established.

Prospection of strains of Bacillus sporogenes in the digestive tract of native crustaceans and characterization of the probiotic potential

The cultivation of marine shrimp is one of the fastest growing activities in the world. However, the emergence of diseases has resulted in a decrease in production and losses for the sector. Probiotics emerged as an option to the use of antibiotics to control these pathogens. The efficiency of applying this technology depends on the characteristics of the bacterial agents and their bioavailability in the shrimp intestine. The objective is to evaluate the viability and efficiency of bacteria isolated from the digestive tract of healthy crustaceans as probiotic agents in the cultivation of shrimp Litopenaeus vannamei. Eighteen strains of the genus Bacillus belonging to the following species were tested: Bacillus sp., B. cereus, B. thuringiensis, B. circulans, B. megaterium, B. subtilis and B. agaridevorans. Bacterial isolates were subjected to characterization as potential probiotics. The test results were considered satisfactory; thus, the tested strains have potential for use as probiotics in shrimp culture. Treatments that used of the genus Bacillus had reduced growth of the genus Vibrio after infection, both in the intestinal contents and in the intestine. With the results obtained, it can be suggested that further research be carried out on the probiotic potential of Bacillus sp.

Myeloid differentiation protein 2 regulates the innate immunity and the disease resistant against Vibrio alginolyticus in Scylla paramamosain

Myeloid differentiation protein 2 (MD2), generally functions as a coreceptor of Toll-like receptor 4 (TLR4), facilitating the activation of TLR4 and the recognition of lipopolysaccharides (LPS) in host organisms. While the role of MD2 in immune activation is well-documented across various species, the specific role of the MD2 homolog in Scylla paramamosain (SpMD2) remains unidentified. In this study, we applied RNA interference to reduce SpMD2 expression, aiming to elucidate its role in immune system of mud crabs. Notably, SpMD2 interference leded to decrease in the hemocyte counts and phagocytic activity, along with increase in apoptosis rates and level of reactive oxygen species (ROS). Furthermore, the activities of key enzymes related to immune, such as superoxide dismutase (SOD), catalase (CAT), phenoloxidase (PO), peroxidase (POD), lysozyme (LZM), and acid phosphatase (ACP), were reduced by SpMD2 knockdown. Following infection with Vibrio alginolyticus, increase of SpMD2 expression level was observed. This was accompanied by alterations in the expression levels of genes related to immune in mud crabs. Challenge experiment with Vibrio alginolyticus showed a higher mortality rate after SpMD2 interference. Our study underscore the critical role of SpMD2 in enhancing the innate immunity and disease resistant in S. paramamosain, advancing our understanding of the innate immune regulatory mechanisms in crustaceans.

Identification and characterization of four Bacillus species from the intestine of hybrid grouper (Epinephelus fuscoguttatus♀ × E. lanceolatus♂), their antagonistic role on common pathogenic bacteria, and effects on intestinal health

As an alternative to the criticized antibiotics, probiotics have been adopted for their eco-friendly nature and ability to enhance host growth and immunity. Nevertheless, reports suggest ineffectiveness in commercially available probiotics since most are from non-fish sources; thus, this study was envisaged to isolate and characterize new Bacillus spp. from the gut of hybrid grouper (Epinephelus fuscoguttatus♀ × Epinephelus lanceolatus♂) which could serve as potential probiotics. The isolation and characterization were performed based on their morphological and biochemical properties, and 16S rRNA sequencing homology analysis. A subsequent 30-day in vivo biosafety feeding trial was conducted to ascertain isolates' non-pathogenicity, as well as their effects on fish growth, and intestinal mucosal microvilli via scanning electron microscopy (SEM) analysis. Four Bacillus spp. strains, namely, B. velezensis strain PGSAK01 (accession number OQ726606), B. stercoris strain PGSAK05 (accession number OQ726607), B. velezensis strain PGSAK17 (accession number OQ726601), and B. subtilis strain PGSAK19 (accession number OQ726605), were identified and characterized in the current study. The strains showed promising probiotic properties such higher adhesion capability, higher thermotolerance, displaying higher survivability to 0.5 % bile, lower pH tolerance, γ-haemolytic activity, and multispecies characteristics. Among the 24 antibiotics tested, while all isolates showed susceptibility to 21, the PGSAK01 strain showed resistance to furazolidone antibiotics. None of the isolates showed possession of i) virulence factor genes encoding enterotoxigenic (hblA, hblC, hblD, nheA, nheB, and entFM) and emetic (cereulide synthetase gene, ces) genes, and ii) streptomycin resistance gene (vat c), ampicillin-resistant genes (mecA and bla), and vancomycin-resistant gene (van B). Nevertheless, the PGSAK01 and PGSAK17 strains showed possession of tek K, cat, and ant(4')-Ia (adenylyltransferase) (except the PGSAK01) resistant genes. All isolates displayed better antimicrobial effects against pathogenic bacteria Streptococcus agalactiae, S. iniae, Vibrio harveyi, and V. alginolyticus. The in vivo biosafety trial involved hybrid grouper fish being grouped into five (average weight 32 ± 0.94 g), namely, the group fed the basal diet void of isolate's supplementation (control), and the remaining four groups fed the basal diet with 1 × 108 CFU/g diet of individual strain PGSAK01, PGSAK05, PGSAK17, and PGSAK19 supplementation. At the end of the study, a significantly higher WGR, K (except the PGSAK01 group), VSI; lysozyme (except PGSAK01 group), total antioxidant activity, alkaline phosphatase, superoxide dismutase enzyme activities; highly dense intestinal mucosal villi (based on the scanning electron microscopy analysis); and significantly lower malondialdehyde levels were witnessed in the isolated treated groups compared to the control, supporting the results obtained in the auto-aggregation and cell-surface hydrophobicity test. This work's results have provided thought-provoking targets; thus, studies involving extensive genome sequencing and functional annotation analysis will be explored to offer unfathomable insights into their mechanisms of action and potential health benefits, further establishing the four Bacillus strains' (PGSAK01, PGSAK05, PGSAK17, and PGSAK19) potential role in probiotic fields and functional foods.

Genomic Characterization of Bacillus pumilus Sonora, a Strain with Inhibitory Activity against Vibrio parahaemolyticus-AHPND and Probiotic Candidate for Shrimp Aquaculture

Acute hepatopancreatic necrosis disease, caused by Vibrio parahaemolyticus strains carrying the pirA and pirB toxin genes (VpAHPND), has been causing great economic losses in Asia and America in the shrimp farming industry. Numerous strains are resistant to antibiotics. However, supplementation with probiotic antagonists has become a more desirable treatment alternative. Fourteen strains of microorganisms were assessed for their potential to inhibit VpAHPND in vitro activity. The bacteria with the highest activity were challenged with VpAHPND-infected Pacific white shrimp Litopenaeus vannamei. Furthermore, the genomic characteristics of probiotic bacteria were explored by whole-genome sequencing. We identified the Sonora strain as Bacillus pumilus, which possesses positive proteolytic and cellulolytic activities that may improve shrimp nutrient uptake and digestion. Challenge trials showed a low cumulative mortality (11.1%). B. pumilus Son has a genome of 3,512,470 bp and 3734 coding sequences contained in 327 subsystems. Some of these genes are related to the biosynthesis of antimicrobial peptides (surfactins, fengycin, schizokinen, bacilibactin, and bacilysin), nitrogen and phosphorus metabolism, and stress response. Our in vitro and in vivo findings suggest that B. pumilus Sonora has potential as a functional probiotic.

Novel lytic bacteriophage AhFM11 as an effective therapy against hypervirulent Aeromonas hydrophila

Several farmed fish species, including carps, tilapia, salmon, and catfish, have experienced significant economic losses in aquaculture due to motile Aeromonas septicemia caused by Aeromonas hydrophila. In the present study, a novel lytic bacteriophage infecting hypervirulent Aeromonas hydrophila (vAh) was isolated and characterized. This is the first report of a phage against vAh. Phage AhFM11 demonstrated lytic activity against both vAh strains and the A. hydrophila reference strain ATCC 35654. The AhFM11 genome was sequenced and assembled, comprising 168,243 bp with an average G + C content of 41.5%. The genome did not harbor any antibiotic resistance genes. Genomic information along with transmission electron microscopy revealed that phage AhFM11 belongs to the Straboviridae family. Therapeutic application of monophage AhFM11 in fish showed 100% survival in injection, 95% in immersion and 93% in oral feeding of phage top-coated feed. Fish and chicken meat spiked with A. hydrophila and phage showed significant reduction of A. hydrophila. These findings support that phage AhFM11 can be used as a biocontrol agent against vAh as an alternative to antibiotics.

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.

Nitrogen and me - How little did we, and do we know about "stikstof - azote - nitrogen"?

This retrospective article reflects on the complex and evolving relationship between humans and nitrogen over several decades. Raised on a Flemish farm, the author's early experiences with nitrogen in agriculture - both its benefits and dangers - laid the foundation for a lifelong interest in this element. The article traverses a broad range of topics related to nitrogen, highlighting its critical role in various historical, agricultural, environmental, and industrial contexts. The narrative begins with a historical overview of nitrogen's role in agriculture and warfare. The development of industrial processes like the Haber and Ostwald methods transformed nitrogen into a key ingredient for both fertilizers and explosives. The dual nature of nitrogen - as a life-giver in agriculture and a destructive component in warfare and also in biodiversity - is an important theme. The article delves into the environmental impacts of nitrogen, particularly in the context of modern agriculture and industrialization. Issues like fertilization, water contamination, and the challenges of managing nitrogenous waste highlight the complex interplay between human activities and environmental health. Technological advancements are explored, including the development of bioaugmentation methods and the potential of genetic engineering in optimizing nitrogen fixation. Throughout the narrative, personal anecdotes are weaved with scientific information, offering a unique perspective on the historical and contemporary challenges of managing nitrogen. The discussion extends to the broader implications of nitrogen management in the context of sustainability, climate change, and global food security and its overall regulatory space. All these considerations call for a re-evaluation of our relationship with nitrogen, advocating for innovative solutions and systemic thinking to address the multifaceted challenges posed by this essential, yet often problematic element.

Siderophores and metallophores: Metal complexation weapons to fight environmental pollution

Siderophores are small molecules of organic nature, released by bacteria to chelate iron from the surrounding environment and subsequently incorporate it into the cytoplasm. In addition to iron, these secondary metabolites can complex with a wide variety of metals, which is why they are commonly studied in the environment. Heavy metals can be very toxic when present in large amounts on the planet, affecting public health and all living organisms. The pollution caused by these toxic metals is increasing, and therefore it is urgent to find practical, sustainable, and economical solutions for remediation. One of the strategies is siderophore-assisted bioremediation, an innovative and advantageous alternative for various environmental applications. This research highlights the various uses of siderophores and metallophores in the environment, underscoring their significance to ecosystems. The study delves into the utilization of siderophores and metallophores in both marine and terrestrial settings (e.g. bioremediation, biocontrol of pathogens, and plant growth promotion), such as bioremediation, biocontrol of pathogens, and plant growth promotion, providing context for the different instances outlined in the existing literature and highlighting their relevance in each field. The study delves into the structures and types of siderophores focusing on their singular characteristics for each application and methodologies used. Focusing on recent developments over the last two decades, the opportunities and challenges associated with siderophores and metallophores applications in the environment were mapped to arm researchers in the fight against environmental pollution.

Effects of adding Bacillus subtilis natto NTU-18 in paste feed on growth, intestinal morphology, gastrointestinal microbiota diversity, immunity, and disease resistance of Anguilla japonica glass eels

Japanese eel, Anguilla japonica, holds significant importance in Taiwanese aquaculture. With the intensification of eel farming, the impact of Edwardsiella tarda has become increasingly severe. Consequently, the abusive use of antibiotics has risen. Bacillus subtilis natto NTU-18, a strain of Bacillus with a high survival rate in feed processing, plays a crucial role in promoting intestinal health through competitive rejection, enhancing immune responses against bacterial pathogens, and improving intestinal health by modulating gastrointestinal microbiota to produce beneficial metabolites of mice and grass carp, Ctenopharyngodon idella. This study investigated the effects of different proportions (control, 0.25 %, 0.5 %, 1 %, and 2 %) of B. subtilis natto NTU-18 added to paste feed on the growth performance, intestinal morphology, and microbiota, expression of immune-related genes, and resistance to E. tarda in Japanese glass eel. The results indicated that the growth performance of all groups with B. subtilis natto NTU-18 added was significantly higher than that of the control group and did not impact the villi morphology. The expression of immune-related genes in the kidney, specifically HSP70 and SOD, was significantly higher from 0.5 % and above than the control; however, no significant differences were observed in CAT, POD, and HSP90. In the liver, significant differences were found in HSP70 and IgM above 0.25 % compared to the control group, with no significant differences in SOD, CAT, POD, and HSP90 among all groups. Additionally, intestinal microbiota analysis revealed that the 2 % additional group had significantly lower diversity than other groups, with Cetobacterium as the dominant species. The challenge test observed that the survival rates of the 0.5 % and 1 % groups were significantly higher. This research suggests that adding 0.5 % and 1 % of B. subtilis natto NTU-18 to the diet is beneficial for Japanese glass eel's immunity, growth performance, and disease resistance.

Synergistic effects of combined probiotics Bacillus pumilis D5 and Leuconostoc mesenteroide B4 on immune enhancement and disease resistance in Litopenaeus vannamei

This study investigated the effects of two distinct probiotics, Leuconostoc mesenteroides B4 (B4) and Bacillus pumilus D5 (D5), along with their combination, on the diet of white shrimp (Litopenaeus vannamei) during an eight-week feeding trial. The diets tested included B4 + dextran at 107 CFU/g feed (the B4 group), D5 alone at 107 CFU/g feed (the D5 group), and a combination of B4 + dextran and D5 at 5 × 106 CFU/g feed each (the B4+dextran + D5 group). Relative to the control group, those administered probiotics exhibited moderate enhancements in growth. By the eighth week, the weight gain for the B4, D5, and B4+D5 groups was 696.50 ± 78.15%, 718.53 ± 130.73%, and 693.05 ± 93.79%, respectively, outperforming the control group's 691.66 ± 31.10% gain. The feed conversion ratio was most efficient in the B4 group (2.16 ± 0.06), closely followed by B4+D5 (2.21 ± 0.03) and D5 (2.22 ± 0.06), with the control group having the highest ratio (2.27 ± 0.03). While phenoloxidase activity was somewhat elevated in the B4 and D5 groups, no significant differences were noted in respiratory burst activity or total hemocyte count across all groups. Challenge tests at weeks 4 and 8 showed that the B4 + D5 combination offered superior protection against AHPND-causing Vibrio parahaemolyticus. The 4-week cumulative survival rate was highest in shrimp treated with B4 + dextran + D5 (56.25%), followed by B4 + dextran (31.25%), control (18.75%), and lowest in D5 (12.5%). By week 8, the B4 + dextran + D5 (43.75%) and B4 + dextran (37.5%) groups significantly outperformed the control group (6.25%, p < 0.05), with no significant difference observed between the D5 group (37.5%) and the control group at day 56. Analysis of the shrimp's foregut microbiota revealed an increase in unique OTUs in the B4 and B4 + D5 groups. Compared to the control, Proteobacteria abundance was reduced in all probiotic groups. Potential pathogens like Vibrio, Bacteroides, Neisseria, Botrytis, Clostridioides, and Deltaentomopoxvirus were detected in the control but were reduced or absent in probiotic groups. Beneficial microbes such as Methanobrevibacter and Dictyostelium in the B4+D5 group, and Sugiyamaella in the B4 group, showed significant increases. Probiotics also led to higher transcript levels of nitric oxide synthase in the hemocytes, and lysozyme and transglutaminase in the midgut, along with lysozyme and α2-macroglobulin in the foregut. Notably, the combined B4 + D5 probiotics synergistically enhanced the expression of superoxide dismutase and prophenoloxidase in the foregut, indicating an improved immune response. In summary, this study demonstrates that the probiotics evaluated, especially when used in combination, significantly boost the expression of specific immune-related genes, enhance the bacterial diversity and richness of the intestine, and thus prevent the colonization and proliferation of Vibrio spp. in L. vannamei.

Dietary Bacillus velezensis T23 fermented products supplementation improves growth, hepatopancreas and intestine health of Litopenaeus vannamei

This study aimed to elucidate the effects of dietary fermented products of Bacillus velezensis T23 on the growth, immune response and gut microbiota in Pacific white shrimp (Litopenaeus vannamei). Shrimp were fed with diets containing fermentation products of B. velezensis T23 at levels of (0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5 g/kg) for 4 weeks, to assess the influence on shrimp growth. The results showed that 0.3 and 0.4 g/kg T23 supplementation improved shrimp growth and feed utilization. Based on these results we selected these three diets (Control, 0.3T23 and 0.4T23) to assess the effect on immune response and gut microbiota of shrimp. Compared with the control, the 0.3T23 and 0.4T23 groups enhanced lipase and α-amylase activities in the gut significantly. Moreover, the 0.4T23 group decreased TAG and MDA levels in hepatopancreas, ALT and AST levels of serum significantly (P < 0.05). In hepatopancreas, CAT and SOD activities were improved observably and the MDA content was reduced markedly in both T23 groups. The expressions of antimicrobial related genes, Cru and peroxinectin in the 0.3T23 group, and proPO and peroxinectin in the 0.4T23 group were up-regulated remarkably (P < 0.05). Moreover, hepatopancreas of shrimp fed with a diet amended with T23 showed a significant down-regulated expression of nf-kb and tnf-α genes, while expressions of tgf-β was considerably up-regulated. Furthermore, serum LPS and LBP contents were reduced markedly in T23 groups. Intestinal SOD and CAT were noteworthy higher in T23 groups (P < 0.05). In the intestine of shrimp fed on the diet enriched with T23 the expression of nf-κb and tnf-α exhibited markedly down-regulated, whereas hif1α was up-regulated (P < 0.05). Besides, in the intestine of shrimp grouped under T23, Cru and peroxinectin genes were markedly up-regulated (P < 0.05). Dietary 0.3 g/kg T23 also upregulated the ratio of Rhodobacteraceae to Vibrionaceae in the gut of the shrimp. Taken together, the inclusion of B. velezensis T23 in the diet of shrimp enhanced the growth and feed utilization, enhanced hepatopancreas and intestine health.

A Review: Microbes and Their Effect on Growth Performance of Litopenaeus vannamei (White Leg Shrimps) during Culture in Biofloc Technology System

In the modern era of Aquaculture, biofloc technology (BFT) systems have attained crucial attention. This technology is used to reduce water renewal with the removal of nitrogen and to provide additional feed. In BFT, microorganisms play a crucial role due to their complex metabolic properties. Pathogens can be controlled through multiple mechanisms using probiotics, which can promote host development and enhance the quality of the culture environment. During culturing in a biofloc technology system, the supplementation of microalgae and its accompanying bacteria plays a beneficial role in reducing nitrogenous compounds. This enhances water quality and creates favorable environmental conditions for specific bacterial groups, while simultaneously reducing the dependency on carbon sources with higher content. The fluctuations in the bacterial communities of the intestine are closely associated with the severity of diseases related to shrimp and are used to evaluate the health status of shrimp. Overall, we will review the microbes associated with shrimp culture in BFT and their effects on shrimp growth. We will also examine the microbial impacts on the growth performance of L. vannamei in BFT, as well as the close relationship between probiotics and the intestinal microbes of L. vannamei.

Bacterial diseases of Asian sea bass (Lates calcarifer): A review for health management strategies and future aquaculture sustainability

The advent of aquaculture has been one of the most significant shifts in world food supply during the last century. Aquaculture has rapidly expanded and become a global food industry, spurred by population expansion, increased seafood consumption, and decreased captured fisheries. Nonetheless, the exponential growth of aquaculture has emerged as a significant contributor to anthropogenic changes. Unexpectedly, the result has focused in the emergence and spread of new diseases. The Asian sea bass (Lates calcarifer) is an economically important species in aquaculture, contributing significantly to the global seafood market. However, bacterial diseases have emerged as a major concern, affecting both wild and cultured populations of this species. The most prevalent bacterial pathogens are streptococcus, vibriosis, nocardiosis, tenacibaculosis, and pot-belly disease. Therefore, this review aims to comprehensively analyze both emerging and non-emerging bacterial diseases affecting L. calcarifer and explore potential management approaches for their control. Through an extensive literature survey and critical evaluation of research findings, this review highlights the current understanding of bacterial diseases in L. calcarifer and proposes strategies for better disease management. In addition, this review looks at the rise and characteristics of aquaculture, the major bacterial pathogens of L. calcarifer and their effects, and the specific attributes of disease emergence in an aquatic rather than terrestrial context. It also considers the potential for future disease emergence in L. calcarifer due to aquaculture expansion and climate changes.

Antimicrobial Activity, Genetic Relatedness, and Safety Assessment of Potential Probiotic Lactic Acid Bacteria Isolated from a Rearing Tank of Rotifers (Brachionus plicatilis) Used as Live Feed in Fish Larviculture

Aquaculture is a rapidly expanding agri-food industry that faces substantial economic losses due to infectious disease outbreaks, such as bacterial infections. These outbreaks cause disruptions and high mortalities at various stages of the rearing process, especially in the larval stages. Probiotic bacteria are emerging as promising and sustainable alternative or complementary strategies to vaccination and the use of antibiotics in aquaculture. In this study, potential probiotic candidates for larviculture were isolated from a rotifer-rearing tank used as the first live feed for turbot larvae. Two Lacticaseibacillus paracasei and two Lactiplantibacillus plantarum isolates were selected for further characterization due to their wide and strong antimicrobial activity against several ichthyopathogens, both Gram-positive and Gram-negative. An extensive in vitro safety assessment of these four isolates revealed the absence of harmful traits, such as acquired antimicrobial resistance and other virulence factors (i.e., hemolytic and gelatinase activities, bile salt deconjugation, and mucin degradation, as well as PCR detection of biogenic amine production). Moreover, Enterobacterial Repetitive Intergenic Consensus-PCR (ERIC-PCR) analyses unveiled their genetic relatedness, revealing two divergent clusters within each species. To our knowledge, this work reports for the first time the isolation and characterization of Lactic Acid Bacteria (LAB) with potential use as probiotics in aquaculture from rotifer-rearing tanks, which have the potential to optimize turbot larviculture and to introduce novel microbial management approaches for a sustainable aquaculture.

Advances in Vibrio-related infection management: an integrated technology approach for aquaculture and human health

Vibrio species pose significant threats worldwide, causing mortalities in aquaculture and infections in humans. Global warming and the emergence of worldwide strains of Vibrio diseases are increasing day by day. Control of Vibrio species requires effective monitoring, diagnosis, and treatment strategies at the global scale. Despite current efforts based on chemical, biological, and mechanical means, Vibrio control management faces limitations due to complicated implementation processes. This review explores the intricacies and challenges of Vibrio-related diseases, including accurate and cost-effective diagnosis and effective control. The global burden due to emerging Vibrio species further complicates management strategies. We propose an innovative integrated technology model that harnesses cutting-edge technologies to address these obstacles. The proposed model incorporates advanced tools, such as biosensing technologies, the Internet of Things (IoT), remote sensing devices, cloud computing, and machine learning. This model offers invaluable insights and supports better decision-making by integrating real-time ecological data and biological phenotype signatures. A major advantage of our approach lies in leveraging cloud-based analytics programs, efficiently extracting meaningful information from vast and complex datasets. Collaborating with data and clinical professionals ensures logical and customized solutions tailored to each unique situation. Aquaculture biotechnology that prioritizes sustainability may have a large impact on human health and the seafood industry. Our review underscores the importance of adopting this model, revolutionizing the prognosis and management of Vibrio-related infections, even under complex circumstances. Furthermore, this model has promising implications for aquaculture and public health, addressing the United Nations Sustainable Development Goals and their development agenda.

In vitro and in vivo evaluation of the efficacies of commercial probiotics and disinfectant against acute hepatopancreatic necrosis disease and luminescent vibriosis in Litopenaeus vannamei

The bioactivities of two commercially available probiotics and one chemical disinfectant were tested against strains of Vibrio parahaemolyticus (VPAHPND) and V. harveyi. This study aimed to determine shrimp pathogenic Vibrios' in vitro and in vivo sensitivities to commercial probiotics and a chemical disinfectant. The probiotics and disinfectant were tested first in vitro, followed by the in vivo trials. Results showed that upon administration of probiotics either through diet or adding into the tank water, the survivability of shrimp was increased during challenge with VPAHPND and V. harveyi. Also, the disinfectant was tested against the same pathogens and showed positive bactericidal effects at 2500 ppm and 5000 ppm. The present findings suggest that adding probiotics to the rearing water or the shrimp feeds effectively prevents infection by lowering the load of pathogenic bacteria. In comparison, the effectiveness of the disinfectant (PUR) depends on its appropriate concentration and timing of application. It is not only limited to rearing water but is also applicable for decontaminating pond liners, tanks, and other paraphernalia.

What role do biocontrol agents with Mg2+ play in the fate of antibiotic resistome and pathogenic bacteria in the phyllosphere?

The contamination of the plant phyllosphere with antibiotics and antibiotic resistance genes (ARGs), caused by application of antibiotics, is a significant environmental issue in agricultural management. Alternatively, biocontrol agents are environmentally friendly and have attracted a lot of interest. However, the influence of biocontrol agents on the phyllosphere resistome remains unknown. In this study, we applied biocontrol agents to control the wildfire disease in the Solanaceae crops and investigated their effects on the resistome and the pathogen in the phyllosphere by using metagenomics. A total of 250 ARGs were detected from 15 samples, which showed a variation in distribution across treatments of biocontrol agents (BA), BA with Mg2+ (T1), BA with Mn2+ (T2), and kasugamycin (T3) and nontreated (CK). The results showed that the abundance of ARGs under the treatment of BA-Mg2+ was lower than that in the CK group. The abundance of cphA3 (carbapenem resistance), PME-1 (carbapenem resistance), tcr3 (tetracycline antibiotic resistance), and AAC (3)-VIIIa (aminoglycoside antibiotic resistance) in BA-Mg2+ was significantly higher than that in BA-Mn2+ (P < 0.05). The abundance of cphA3, PME_1, and tcr3 was significantly negatively related to the abundance of the phyllosphere pathogen Pseudomonas syringae (P < 0.05). We also found that the upstream and downstream regions of cphA3 were relatively conserved, in which rpl, rpm, and rps gene families were identified in most sequences (92%). The Ka/Ks of cphA3 was 0 in all observed sequences, indicating that under the action of purifying selection, nonsynonymous substitutions are often gradually eliminated in the population. Overall, this study clarifies the effect of biocontrol agents with Mg2+ on the distribution of the phyllosphere resistome and provides evolutionary insights into the biocontrol process.

IMPORTANCE

Our study applied metagenomics analysis to examine the impact of biocontrol agents (BAs) on the phyllosphere resistome and the pathogen. Irregular use of antibiotics has led to the escalating dissemination of antibiotic resistance genes (ARGs) in the environment. The majority of BA research has focused on the effect of monospecies on the plant disease control process, the role of the compound BA with nutrition elements in the phyllosphere disease, and the resistome is still unknown. We believe BAs are eco-friendly alternatives for antibiotics to combat the transfer of ARGs. Our results revealed that BA-Mg2+ had a lower relative abundance of ARGs compared to the CK group, and the phyllosphere pathogen Pseudomonas syringae was negatively related to three specific ARGs, cphA3, PME-1, and tcr3. These three genes also present different Ka/Ks. We believe that the identification of the distribution and evolution modes of ARGs further elucidates the ecological role and facilitates the development of BAs, which will attract general interest in this field.

Present Status, Limitations, and Prospects of Using Streptomyces Bacteria as a Potential Probiotic Agent in Aquaculture

Streptomyces is a Gram-positive bacterium, belonging to the family Streptomycetaceae and order Streptomycetales. Several strains from different species of Streptomyces can be used to promote the health and growth of artificially cultured fish and shellfish by producing secondary metabolites including antibiotics, anticancer agents, antiparasitic agents, antifungal agents, and enzymes (protease and amylase). Some Streptomyces strains also exhibit antagonistic and antimicrobial activity against aquaculture-based pathogens by producing inhibitory compounds such as bacteriocins, siderophores, hydrogen peroxide, and organic acids to compete for nutrients and attachment sites in the host. The administration of Streptomyces in aquaculture could also induce an immune response, disease resistance, quorum sensing/antibiofilm activity, antiviral activity, competitive exclusion, modification in gastrointestinal microflora, growth enhancement, and water quality amelioration via nitrogen fixation and degradation of organic residues from the culture system. This review provides the current status and prospects of Streptomyces as potential probiotics in aquaculture, their selection criteria, administrative methods, and mechanisms of action. The limitations of Streptomyces as probiotics in aquaculture are highlighted and the solutions to these limitations are also discussed.

Antibiotic susceptibility and resistance genes profiles of Vagococcus salmoninarum in a rainbow trout (Oncorhyncus mykiss, Walbaum) farm

Disease outbreaks negatively affect fish production. Antimicrobial agents used in the treatment of diseases become ineffective over time because of antibiotic resistance developed by bacteria distributed in the aquaculture environment. This study was conducted for 4 months (cold period) in a fish farm to detect the fish disease, cold water streptococcosis. In the study, four brood stock showing disease signs were detected. Bacteria isolates were obtained and identified as Vagococcus salmoninarum. Antimicrobial susceptibility of V. salmoninarum was tested and antibiotic resistance gene profiles of V. salmoninarum isolates were screened. The phylogenetic relation of the isolates with the previously reported strains was evaluated. Antibiotic resistance developed by pathogenic bacteria is distributed in the aquaculture environment. The transfer of resistance genes from one bacterium to another is very common. This situation causes the antimicrobial agents used in the treatment of diseases to become ineffective over time. The disc diffusion test showed that all four isolates developed resistance to 13 (FFC30, AX25, C30, E15, CF30, L2, OX1, S10, T30, CRO30, CC2, PT15 and TY15) of the evaluated antibiotics and were about to develop resistance to six others (AM 10, FM 300, CFP75, SXT25, APR15 and TE30). Furthermore, antibiotic resistance genes tetA, sul1, sul2, sul3, dhfr1, ereB and floR were detected in the isolated strain. Moreover, the phylogenetic analysis showed that isolated V. salmoninarum strain (ESN1) was closely related to the bacterial strains isolated from USA and Jura.

Evaluation of different probiotics on growth, body composition, antioxidant capacity, and histoarchitecture of Mugil capito

We investigated the dietary effects of the single application of Saccharomyces cerevisiae, Lactobacillus bulgaricus, and their combination on growth, proximate composition of whole fish body, antioxidant defense, and histoarchitecture of hapa-reared Mugil capito. Healthy fish (Fish weighed = 10.30 ± 0.10 g at first) were randomly allocated into 4 equal groups, each with three replicates. These groups were designed as follows: (1) a group fed a basal diet without probiotics (control), (2) a group fed a diet containing S. cerevisiae (4 g/kg diet), (3) a group fed a diet containing L. bulgaricus (2 g/kg diet), and (4) the last group fed a diet containing a combination of both, all for a duration of 60 days. Probiotic-treated groups showed significantly better growth and nutrition utilization than the control group. Significant differences were observed in the crude fat and crude protein contents among the groups, with the combination group exhibiting the highest levels. However, there were no significant variations in ash content across all groups. The highest hepatic antioxidant capacity (superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX) enzyme activities) was observed in the combination group. Thiobarbituric acid reactive substance (TBARS) concentrations were decreased significantly in all probiotic groups, suggesting improved oxidative stress resilience in these groups. The histomorphological analysis of the hepatopancreatic tissues revealed well-arranged parenchyma, increased glycogen storage, and melanomacrophage centers in probiotic-treated groups, particularly the combined probiotics group. Furthermore, the probiotic supplementation improved the histoarchitecture of the intestinal villi compared to the control group. To put it briefly, combined dietary administration of these probiotics improved growth, body composition, antioxidant defenses, and hepatic and intestinal health in hapa-reared M. capito, highlighting their promising role in promoting welfare and productivity.

Interwoven processes in fish development: microbial community succession and immune maturation

Fishes are hosts for many microorganisms that provide them with beneficial effects on growth, immune system development, nutrition and protection against pathogens. In order to avoid spreading of infectious diseases in aquaculture, prevention includes vaccinations and routine disinfection of eggs and equipment, while curative treatments consist in the administration of antibiotics. Vaccination processes can stress the fish and require substantial farmer's investment. Additionally, disinfection and antibiotics are not specific, and while they may be effective in the short term, they have major drawbacks in the long term. Indeed, they eliminate beneficial bacteria which are useful for the host and promote the raising of antibiotic resistance in beneficial, commensal but also in pathogenic bacterial strains. Numerous publications highlight the importance that plays the diversified microbial community colonizing fish (i.e., microbiota) in the development, health and ultimately survival of their host. This review targets the current knowledge on the bidirectional communication between the microbiota and the fish immune system during fish development. It explores the extent of this mutualistic relationship: on one hand, the effect that microbes exert on the immune system ontogeny of fishes, and on the other hand, the impact of critical steps in immune system development on the microbial recruitment and succession throughout their life. We will first describe the immune system and its ontogeny and gene expression steps in the immune system development of fishes. Secondly, the plurality of the microbiotas (depending on host organism, organ, and development stage) will be reviewed. Then, a description of the constant interactions between microbiota and immune system throughout the fish's life stages will be discussed. Healthy microbiotas allow immune system maturation and modulation of inflammation, both of which contribute to immune homeostasis. Thus, immune equilibrium is closely linked to microbiota stability and to the stages of microbial community succession during the host development. We will provide examples from several fish species and describe more extensively the mechanisms occurring in zebrafish model because immune system ontogeny is much more finely described for this species, thanks to the many existing zebrafish mutants which allow more precise investigations. We will conclude on how the conceptual framework associated to the research on the immune system will benefit from considering the relations between microbiota and immune system maturation. More precisely, the development of active tolerance of the microbiota from the earliest stages of life enables the sustainable establishment of a complex healthy microbial community in the adult host. Establishing a balanced host-microbiota interaction avoids triggering deleterious inflammation, and maintains immunological and microbiological homeostasis.

Harnessing probiotics and prebiotics as eco-friendly solution for cleaner shrimp aquaculture production: A state of the art scientific consensus

In recent years, the advancement and greater magnitude of products, which led to the intensification in shrimp aquaculture is the result of utilization of modern tools and synchronization with other fields of science like microbiology and biotechnology. This intensification led to the elevation of disorders such as the development of several diseases and complications associated with biofouling. The use of antibiotics in aquaculture is discouraged due to their certain hazardous paraphernalia. Consequently, there has been a growing interest in exploring alternative strategies, with probiotics and prebiotics emerging as environmentally friendly substitutes for antibiotic treatments in shrimp aquaculture. This review highlighted the results of probiotics and prebiotics administration in the improvement of water quality, enhancement of growth and survival rates, stress resistance, health status and disease resistance, modulation of enteric microbiota and immunomodulation of different shrimp species. Additionally, the study sheds light on the comprehensive role of prebiotics and probiotics in elucidating the mechanistic framework, contributing to a deeper understanding of shrimp physiology and immunology. Besides their role in growth and development of shrimp aquaculture, the eco-friendly behavior of prebiotics and probiotics have made them ideal to control pollution in aquaculture systems. This comprehensive exploration of prebiotics and probiotics aims to address gaps in our understanding, including the economic aspects of shrimp aquaculture in terms of benefit-cost ratio, and areas worthy of further investigation by drawing insights from previous studies on different shrimp species. Ultimately, this commentary seeks to contribute to the evolving body of knowledge surrounding prebiotics and probiotics, offering valuable perspectives that extend beyond the ecological dimensions of shrimp aquaculture.

Exploring the role and mechanism of potential probiotics in mitigating the shrimp pathogens

Shrimp aquaculture has rapidly developed into a significant industry worldwide, providing not only financial gain and high-quality food but also tens of thousands of trained and competent workers. Frequent diseases are now regarded as a significant risk factor for shrimp aquaculture, as they have the potential to significantly reduce shrimp production and result in economic losses. Over the years various traditional methods including the use of antibiotics have been followed to control diseases yet unsuccessful. Probiotic is considered potential supplements for shrimps during farming, they may also act beneficially as disease control and increased production. Probiotics are described as a live microbial supplement that benefits the host by modifying the microbial population associated with the host and its ambient. The present state of research about probiotics demonstrates notable impacts on the immune defences of the host's gastrointestinal system, which play a crucial role in safeguarding against diseases and managing inflammation inside the digestive tract. In the past ten years, many studies on probiotics have been published. However, there is a lack of information about the processes by which probiotics exert their effects in aquaculture systems, with only limited elucidations being offered. This study explores the variety of procedures behind the positive effects of probiotics in shrimp culture. These mechanisms include the augmentation of the immune system, control of growth, antagonistic action against pathogens, competitive exclusion, and modification of the gut microbiota. Mechanisms involved in the probiotic mode of action are mostly interlinked. This provides a greater understanding of the importance of probiotics in shrimp culture as an environmentally friendly practice.

Biofloc Technology (BFT) in Aquaculture: What Goes Right, What Goes Wrong? A Scientific-Based Snapshot

Aquaculture is a crucial industry that can help meet the increasing demand for aquatic protein products and provide employment opportunities in coastal areas and beyond. If incorrectly manage, traditional aquaculture methods can have negative impacts on the environment and natural resources, including water pollution and overuse of wild fish stocks as aquafeed ingredients. Biofloc technology (BFT) may offer a promising solution to some of these challenges by promoting a cleaner and sustainable production system. BFT converts waste into bioflocs, which serve as a natural food source for fish and shrimp within the culture system, reducing the need for external inputs, such as feed and chemicals. Moreover, BFT has the potential to improve yields and economic performance while promoting efficient resource utilization, such as water and energy. Despite its numerous advantages, BFT presents several challenges, such as high energy demand, high initial/running costs, waste (effluent, suspended solids, and sludge) management, opportunistic pathogens (vibrio) spread, and a lack of understanding of operational/aquatic/microbial dynamics. However, with further training, research, and innovation, these challenges can be overcome, and BFT can become a more widely understood and adopted technique, acting as an effective method for sustainable aquaculture. In summary, BFT offers a cleaner production option that promotes circularity practices while enhancing performance and economic benefits. This technique has the potential to address several challenges faced by the aquaculture industry while ensuring its continued growth and protecting the environment. A more broad BFT adoption can contribute to meeting the increasing demand for aquaculture products while reducing the industry's negative impact on the environment and natural resources. In this context, this review provides an overview of the advantages and challenges of BFT and highlights key technical, biological, and economic aspects to optimize its application, promote further adoption, and overcome the current challenges.

Utilization of Sugarcane Bagasse (Saccharum officinarum Linn.) as a Carbon Source in Biofloc System of Vaname Shrimp Litopenaeus vannamei

<b>Background and Objective:</b> Vaname shrimp (<i>Litopenaeus vannamei</i>) is one of the main economic commodities in aquaculture in the world. Biofloc is a cultivation technology that effectively improves the growth and health status of vaname shrimp. This research aimed to analyze the use of bagasse as a carbon source in the biofloc system for white shrimp cultivation. <b>Materials and Methods:</b> The shrimp used were 18 g/individual shrimp obtained from the Bone Marine and Fisheries Polytechnic Pond. Sugarcane bagasse processed from sugar factory waste was dried in an oven at 60°C and ground using a flouring machine. The research treatments included biofloc application where sugarcane bagasse played a role as a carbon source (L), biofloc application where wheat flour's role was as a carbon source (T) and control or no biofloc application (K). <b>Results:</b> This research showed that sugarcane bagasse could be used as a carbon source for white shrimp biofloc cultivation where the growth value tended to be the same as wheat flour. Total hemolytic count (THC) and shrimp survival in sugarcane bagasse biofloc were as good as wheat flour biofloc. Sugarcane bagasse biofloc had the same ability as wheat flour biofloc in reducing ammonia levels in the rearing media. Sugarcane bagasse biofloc had the same ability as wheat flour biofloc in reducing ammonia levels in the rearing media. The application of bagasse had no effect on temperature, pH, dissolved oxygen and salinity of the rearing media because this treatment was in the optimal range for the growth of vaname shrimp. <b>Conclusion:</b> Sugarcane bagasse has the potential to be a carbon source in biofloc systems because it could improve growth, health status, survival and water quality.

From microbiome composition to functional engineering, one step at a time

SUMMARYCommunities of microorganisms (microbiota) are present in all habitats on Earth and are relevant for agriculture, health, and climate. Deciphering the mechanisms that determine microbiota dynamics and functioning within the context of their respective environments or hosts (the microbiomes) is crucially important. However, the sheer taxonomic, metabolic, functional, and spatial complexity of most microbiomes poses substantial challenges to advancing our knowledge of these mechanisms. While nucleic acid sequencing technologies can chart microbiota composition with high precision, we mostly lack information about the functional roles and interactions of each strain present in a given microbiome. This limits our ability to predict microbiome function in natural habitats and, in the case of dysfunction or dysbiosis, to redirect microbiomes onto stable paths. Here, we will discuss a systematic approach (dubbed the N+1/N-1 concept) to enable step-by-step dissection of microbiome assembly and functioning, as well as intervention procedures to introduce or eliminate one particular microbial strain at a time. The N+1/N-1 concept is informed by natural invasion events and selects culturable, genetically accessible microbes with well-annotated genomes to chart their proliferation or decline within defined synthetic and/or complex natural microbiota. This approach enables harnessing classical microbiological and diversity approaches, as well as omics tools and mathematical modeling to decipher the mechanisms underlying N+1/N-1 microbiota outcomes. Application of this concept further provides stepping stones and benchmarks for microbiome structure and function analyses and more complex microbiome intervention strategies.

Administration of probiotics affects Artemia franciscana metanauplii intestinal ultrastructure and offers resistance against a Photobacterium damselae ssp. piscicida induced oxidative stress response

The effects of Photobacterium damselae ssp. piscicida (Phdp) on immune responses and intestinal ultrastructure of Artemia franciscana following infection and their amelioration by the probiotic bacteria Bacillus subtilis, Lactobacillus plantarum and Lactococcus lactis were evaluated. Pathogen growth inhibition in coculture with each probiotic and its virulence against Artemia were confirmed with an LC50 of 105 CFU mL-1. Phdp administration to Artemia at sublethal levels resulted in depletion of superoxide dismutase, glutathione reductase, glutathione transferase and phenoloxidase activities, extensive lipid peroxidation and reduced survival. Following a combined administration of each probiotic and the pathogen, enzyme activities and survival were significantly higher, while lipid peroxidation was reduced, compared to the infected group with no probiotic treatment (P < 0.05). The transmission electron microscopy study revealed that pathogen infection resulted in disarranged and fragmented microvilli, formation of empty or pathogen containing cytoplasmic vacuoles and damaged mitochondria. In the probiotic-treated and Phdp-infected series, intestinal cells showed normal appearance, except for the presence of pathogen-containing vacuoles and highly ordered but laterally stacked microvilli. The results of the present study indicate that Phdp induces cell death through an oxidative stress response and probiotics enhance Artemia immune responses to protect it against the Phdp induced damage.

Utilisation of probiotics for disease management in giant freshwater prawn (Macrobrachium rosenbergii): Administration methods, antagonistic effects and immune response

The giant freshwater prawn (Macrobrachium rosenbergii) is a high-yielding prawn variety well-received worldwide due to its ability to adapt to freshwater culture systems. Macrobrachium rosenbergii is an alternative to shrimp typically obtained from marine and brackish aquaculture systems. However, the use of intensive culture systems can lead to disease outbreaks, particularly in larval and post-larval stages, caused by pathogenic agents such as viruses, bacteria, fungi, yeasts and protozoans. White tail disease (viral), white spot syndrome (viral) and bacterial necrosis are examples of economically significant diseases. Given the increasing antibiotic resistance of disease-causing microorganisms, probiotics have emerged as promising alternatives for disease control. Probiotics are live active microbes that are introduced into a target host in an adequate number or dose to promote its health. In the present paper, we first discuss the diseases that occur in M. rosenbergii production, followed by an in-depth discussion on probiotics. We elaborate on the common methods of probiotics administration and explain the beneficial health effects of probiotics as immunity enhancers. Moreover, we discuss the antagonistic effects of probiotics on pathogenic microorganisms. Altogether, this paper provides a comprehensive overview of disease control in M. rosenbergii aquaculture through the use of probiotics, which could enhance the sustainability of prawn culture.

Nutritional Value of Microalgae and Cyanobacteria Produced with Batch and Continuous Cultivation: Potential Use as Feed Material in Poultry Nutrition

Recently, the demand for new alternative feedstuffs that do not contain chemical residue and are not genetically modified has been increased for sustainability in poultry production. In this respect, the usage of algae as animal feed is very promising as an alternative feed ingredient that reduces pollutant gases from animal production facilities. The aim of the current study is to investigate the usage possibility of algae, through determining nutritional value and production cost, as a feed ingredient in poultry nutrition. Three microalgae species, including Scenedesmus sp., Ankistrodesmus sp., and Synechococcaceae, were produced with batch and continuous cultivation to determine the difference in the lipid, protein, carbohydrate, fatty acid, and amino acid profiles, as well as the color characteristics and production cost. The highest lipid content of 72.5% was observed in algae biomass produced from Synechococcaceae with batch cultivation, whereas the highest protein level was found in algae biomass produced by Synechococcaceae under continuous cultivation practice (25.6%). The highest content of PUFA was observed in Scenedesmus sp. harvested from both batch and continuous cultivation (35.6 and 36.2%), whereas the lowest content of PUFA was found in Synechococcaceae harvested with continuous cultivation (0.4%). Continuously cultivated of Scenedesmus sp. had higher carbohydrate content than batch-cultivated Scenedesmus sp. (57.2% vs. 50.1%). The algae biomass produced from Synechococcaceae was found to have a higher content of essential amino acids, except lysine and histidine, compared to Scenedesmus sp. and Ankistrodesmus sp. Cultivation practices also affected the amino acid level in each algae species. The continuous cultivation practice resulted in a higher level of essential amino acids, except glycine. Synechococcaceae had richer essential amino acid content except for proline and ornithine, whereas continuous cultivation caused an incremental increase in non-essential amino acids. The lightness value was found to be the lowest (13.9) in Scenedesmus sp. that was continuously cultivated. The current study indicated that Scenedesmus sp. could be offered for its high PUFA and lysine content, whereas Synechococcaceae could have potential due to its high content of methionine and threonine, among the investigated microalgae and Cyanobacteria.

Biotic countermeasures that rescue Nannochloropsis gaditana from a Bacillus safensis infection

The natural assemblage of a symbiotic bacterial microbiome (bacteriome) with microalgae in marine ecosystems is now being investigated as a means to increase algal productivity for industry. When algae are grown in open pond settings, biological contamination causes an estimated 30% loss of the algal crop. Therefore, new crop protection strategies that do not disrupt the native algal bacteriome are needed to produce reliable, high-yield algal biomass. Bacteriophages offer an unexplored solution to treat bacterial pathogenicity in algal cultures because they can eliminate a single species without affecting the bacteriome. To address this, we identified a highly virulent pathogen of the microalga Nannochloropsis gaditana, the bacterium Bacillus safensis, and demonstrated rescue of the microalgae from the pathogen using phage. 16S rRNA amplicon sequencing showed that phage treatment did not alter the composition of the bacteriome. It is widely suspected that the algal bacteriome could play a protective role against bacterial pathogens. To test this, we compared the susceptibility of a bacteriome-attenuated N. gaditana culture challenged with B. safensis to a N. gaditana culture carrying a growth-promoting bacteriome. We showed that the loss of the bacteriome increased the susceptibility of N. gaditana to the pathogen. Transplanting the microalgal bacteriome to the bacteriome-attenuated culture reconstituted the protective effect of the bacteriome. Finally, the success of phage treatment was dependent on the presence of beneficial bacteriome. This study introduces two synergistic countermeasures against bacterial pathogenicity in algal cultures and a tractable model for studying interactions between microalgae, phages, pathogens, and the algae microbiome.

Bacterial networks in Atlantic salmon with Piscirickettsiosis

An unbalanced composition of gut microbiota in fish is hypothesized to play a role in promoting bacterial infections, but the synergistic or antagonistic interactions between bacterial groups in relation to fish health are not well understood. We report that pathogenic species in the Piscirickettsia, Aeromonas, Renibacterium and Tenacibaculum genera were all detected in the digesta and gut mucosa of healthy Atlantic salmon without clinical signs of disease. Although Piscirickettsia salmonis (and other pathogens) occurred in greater frequencies of fish with clinical Salmonid Rickettsial Septicemia (SRS), the relative abundance was about the same as that observed in healthy fish. Remarkably, the SRS-positive fish presented with a generalized mid-gut dysbiosis and positive growth associations between Piscirickettsiaceae and members of other taxonomic families containing known pathogens. The reconstruction of metabolic phenotypes based on the bacterial networks detected in the gut and mucosa indicated the synthesis of Gram-negative virulence factors such as colanic acid and O-antigen were over-represented in SRS positive fish. This evidence indicates that cooperative interactions between organisms of different taxonomic families within localized bacterial networks might promote an opportunity for P. salmonis to cause clinical SRS in the farm environment.

Beneficial microbes to suppress Vibrio and improve the culture performance of copepod Tigriopus japonicus Mori

The use of beneficial microbes, i.e., probiotics, to reduce pathogens and promote the performance of the target species is an important management strategy in mariculture. This study aimed to investigate the potential of four microbes, Debaryomyces hansenii, Ruegeria mobilis, Lactobacillus plantarum, and Bacillus subtilis, to suppress Vibrio and increase survival, population growth and digestive enzyme activity (protease, lipase, and amylase) in the harpacticoid copepod, Tigriopus japonicus. Copepod, T. japonicus stock culture with an initial mean density of 50 individual/mL (25 adult male and 25 adult female) was distributed into five treatments (i.e., four experimental and a control, each with four replicates; repeated twice) using 20 beakers (100 mL capacity each). The copepods were fed a mixture of the dinoflagellate Alexandrium tamarense and the diatom Phyaeodactylum tricornutum (3 × 104 cells/mL-1). Each microbe's concentration was adjusted at 108 CFU/mL-1 and applied to the culture condition. D. hansenii, L. plantarum, and B. subtilis all improved the copepods' survival and population growth, likely by including a higher lipase activity (P < 0.05). In contrast, using R. mobilis did not improve the copepod's culture performance compared to control. B. subtilis was the most effective in decreasing the copepod's external and internal Vibrio loading. The probiotic concentrations in the copepod decreased within days during starvation, suggesting that routine re-application of the probiotics would be needed to sustain the microbial populations and the benefits they provide. Our results demonstrated that D. hansenii and B. subtilis are promising probiotics for mass copepod culture as live food for mariculture purposes.

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.

Screening, Identification, and Growth Promotion of Antagonistic Endophytes Associated with Chenopodium quinoa Against Quinoa Pathogens

Fungal disease is one of the important reasons for crop yield reduction. Isolation of important endophytes with biocontrol and growth-promoting effects is of great significance for the exploitation of beneficial microbial resources and the biological control of crop fungal diseases. In this study, endophytes from roots, stems, and leaves of quinoa at different growth and development stages were isolated and purified; then the antagonistic activity and growth-promoting characteristics of antagonistic endophytes were determined. Finally, the antagonistic endophytes were identified by morphological characteristics and ITS/16S rRNA sequence analysis. Our results showed that 122 endophytic fungi and 371 endophytic bacteria were isolated from quinoa, of which three endophytic fungi and seven endophytic bacteria were screened that had inhibitory activity against quinoa pathogenic fungi. Most of the antagonistic strains could produce indole-3 acetic acid and had the ability to dissolve organic phosphorus. In addition, the bacterial suspension of endophytic bacteria had the ability to promote the seed germination and plant growth of quinoa. The endophytic fungi with antagonistic activity were identified as Penicillium raperi and P. pulvillorum; the endophytic bacteria were identified as Bacillus paralicheniformis, B. tequilensis, and B. velezensis, respectively. The strains of quinoa endophytes in this study can provide rich microbial resources and a theoretical basis for biological control of plant fungal diseases and agricultural production.

De novo whole transcriptome analysis of Aeromonas hydrophila isolated from the gut of an infected Labeo rohita

Aeromonas hydrophila is a major generalist bacterial pathogen causing severe infections and mortalities in aquatic animals. Its genome, which was the first to be sequenced from the Aeromonas genus, may serve as a model for studying pathogenic mechanisms. To explore the pathogen-host fitness mechanism of bacterium, a comprehensive comparative transcriptome ecotype analysis of A. hydrophila isolated from the gut of Labeo rohita during infection was performed. Special characteristics in gene expression, gene ontology terms and expression of pathogenesis-associated genes, including genes encoding secreted proteins, candidate effectors, hydrolases, and proteins involved in secondary metabolite production were revealed. Among the database, 6,533 were gene ontology (GO) annotated, while 1,480 were not allocated in any GO terms. Investigation on GO illustrated that the articulated genes were improved with molecular function, cellular components, and biological processes. Further bioinformatics analysis identified the outer membrane protein genes (ompA, ompts, ompw, omp38, and omp48), cytotoxin, amylase, and lipase genes. Overall, this work allowed to designate, for the first time, a global view on the pathogenicity of Aeromonas hydrophila during infection. Furthermore, the study provides information on the fitness of A. hydrophila, a severe pathogen with a wide host range.

Effect of eco-friendly probiotics-supplemented rapeseed meal-based diet on the performance of Catla catla fingerlings

Ever-increasing human population compels the researchers to search for alternative food sources such as fish meat. For increase of fish growth and proper feed utilization, probiotics were added in rapeseed meal-based diet in current trial for proper digestion and absorption of nutrients in fish and ultimately higher growth with lower aquatic pollution. Fish gut microbiota is important for the feed utilization and absorption in body for higher growth. A 70-day study was conducted to investigate the effects of probiotics-supplemented rapeseed meal-based diet on growth performance, digestibility of nutrients, and absorption of minerals in Catla catla fingerlings with lowering water pollution level. Six test diets were prepared by using different levels of multi-strain probiotics i.e. 0, 1, 2, 3, 4 and 5 g/kg (0.0-0.5%) in rapeseed meal-based diet. At the rate of 4% of live wet weight, Catla fingerlings were fed two times a day and faeces samples from each tank were collected. According to the results, it was observed that probiotics supplementation (@2 g/kg) in rapeseed meal-based diet resulted with improvement in nutrient digestibility (CP, 72%; fat, 75% and GE, 70%), mineral absorption (Ca, 72%; Na, 76%; K, 70% and P, 70%), specific growth rate (SGR, 1.55), improved feed conversion ratio (FCR, 1.22) and weight gain percentage (WG%, 303%) of fingerlings. It was also noticed that probiotics supplementation decreased the discharge of minerals and nutrient through faeces, as compared to control diet; hence, it plays a significant role in reducing water pollution. On the basis of these results, it was concluded that probiotics inclusion at level of 2 g/kg was useful to formulate the cost effective and eco-friendly fish feed with the maximum improvement in growth and fish health by using rapeseed meal-based diet, as compared to control and other test diets.

Host gut-derived Bacillus probiotics supplementation improves growth performance, serum and liver immunity, gut health, and resistive capacity against Vibrio harveyi infection in hybrid grouper (♀Epinephelus fuscoguttatus × ♂Epinephelus lanceolatus)

Several reports have revealed the vital role that probiotics play in fish growth and health. However, few works are available for host gut-derived probiotics on the growth, immunity, and gut microbiota of fish, especially in hybrid grouper (♀Epinephelus fuscoguttatus × ♂Epinephelus lanceolatus) due to their isolation difficulty and functional verification. This study aimed at assessing 3 host gut-derived Bacillus species' effects on the growth, immune and antioxidant-biochemical responses, haematological parameters, intestinal morphology, immune-related gene expression, gut microbiota, and disease resistance against Vibrio harveyi in hybrid grouper. A total of 480 hybrid grouper (initial weight = 9.03 ± 0.02 g) were randomly allotted into 4 groups, namely, the group fed a basal diet without probiotic inclusion (control, B0), the group fed the basal diet with Bacillus velezensis GPSAK4 (BV), the group fed the basal diet with Bacillus subtilis GPSAK9 (BS), and the group fed the basal diet with Bacillus tequilensis GPSAK2 (BT) strains at 1.0 × 10⁹ CFU/g. After a 6-week feeding trial, the results revealed significant improvements (P < 0.05) in the growth performance, whole fish-body proximate composition, blood haematological parameters, serum, liver, and intestinal biochemical indexes, intestinal morphology, and protection against V. harveyi pathogen in the probiotic-treated groups compared with the untreated. Additionally, the expressions of intestinal tight junction genes (occludin and ZO1), pro- and anti-inflammatory genes, including IL1β, IL6, IL8, TNFα, MyD88, IL10, and TGFβ, were upregulated (P < 0.05) after Bacillus species administration. Host gut-derived Bacillus supplementation shaped the gut microbiota by significantly increasing (P < 0.05) the relative abundance of Proteobacteria, Bacteroidetes, Actinobacteria (except the BS group), Acidobacteria (except the BT group), Cyanobacteria (except the BV and BT groups), and Verrucomicrobia phyla, as well as known beneficial genera (Romboutsia, Turicibacter, Epulopiscium, Clostridium_sensu_stricto 1 and 13, Lactobacillus, and Bacillus), but significantly decreased (P < 0.05) the abundance of Firmicutes, Chloroflexi, and Fusobacteria phyla, and purported pathogenic genera (Staphylococcus and Photobacterium) compared with the control group. Collectively, the results suggest that B. velezensis GPSAK4, B. subtilis GPSAK9 (especially this strain), B. tequilensis GPSAK2 dietary supplementation at 1.0 × 10⁹ CFU/g has positive effects on the intestinal health of hybrid grouper via microbial composition modulation, thus enhancing the assimilation and absorption of nutrients to boost fish growth, immunity, and disease resistance.

Effects of Bacillus halophilus on growth, intestinal flora and metabolism of Larimichthys crocea

The incorporation of probiotics into the diet of large yellow croaker has been demonstrated by several studies to confer partial disease resistance. Bacillus halophilic isolated from the intestinal flora was used to study its effects on performance growth indicators, intestinal tissue structure, intestinal flora and the metabolism of Larimichthys crocea. A total of 180 fishes with an initial body weight of (164.00 ± 54.00) g were fed diets with three different concentrations of Bacillus halophilic: 0 cfu/mL (FC0, control group), 108 cfu/mL (FC8, treatment group), and 1012 cfu/mL (FC12, treatment group). The results showed that there were no significant differences in specific growth rate among all groups (P > 0.05). Compared to the FC0 group, the final body weight and Weight gain rate were significantly higher in FC8 and FC12 groups (P < 0.05). The Survival of the FC12 group significantly improved (P < 0.05). Compared to the FC0 group, crude protein content in muscle of the FC8 group significantly increased (P < 0.05), crude fat content significantly increased in the FC12 group (P < 0.05), crude protein content in whole fish experimental groups significantly increased (P < 0.05), and ash content significantly increased in the FC8 group (P < 0.05). In terms of antioxidant ability, the content of LZM in blood increased significantly in the FC8 group (P < 0.05), GSH content in liver of the FC12 group increased significantly (P < 0.05), while the content of MDA and AKP in blood and liver had no significant difference (P > 0.05). At the level of intestinal structure, there were no significant differences in villus height, crypt depth and goblet cell number between control group and treatment groups (P > 0.05). At the phylum level, Firmicutes was the dominant phylum, and the genus level, Lactobacillus and Bacteroides were the dominant bacteria in FC8 and FC12. A total of 1070 metabolites were identified, among which lipid metabolites accounted for 46.7%. Metabolites were involved in six main ways, mainly related to the metabolism of amino acids and lipids. The correlation analysis between microbes and metabolites showed that the intestinal flora of Larimichthys crocea could promote the synthesis of metabolites, among which Bacteroides and Megamonas could promote the synthesis of beneficial metabolites such as amino acids and vitamins. Through this study, we found that Bacillus halophilic can significantly improve growth, the antioxidant immunity ability and promote the expression of growth related metabolites, with the FC12 group being the better successful.

Quorum sensing signals: Aquaculture risk factor

Bacteria produce several virulence factors and cause massive mortality in fish and crustaceans. Abundant quorum sensing (QS) signals and high cell density are essentially required for the production of such virulence factors. Although several strategies have been developed to control aquatic pathogens through antibiotics and QS inhibition, the impact of pre‐existing QS signals in the aquatic environment has been overlooked. QS signals cause detrimental effects on mammalian cells and induce cell death by interfering with multiple cellular pathways. Moreover, QS signals not only function as a messenger, but also annihilate the functions of the host immune system which implies that QS signals should be designated as a major virulence factor. Despite QS signals' role has been well documented in mammalian cells, their impact on aquatic organisms is still at the budding stage. However, many aquatic organisms produce enzymes that degrade and detoxify such QS signals. In addition, physical and chemical factors also determine the stability of the QS signals in the aqueous environment. The balance between QS signals and existing QS signals degrading factors essentially determines the disease progression in aquatic organisms. In this review, we highlight the impact of QS signals on aquatic organisms and further discussed potential alternative strategies to control disease progression.

Dietary Inclusion of Halobacterium salinarum Modulates Growth Performances and Immune Responses in Farmed Gilthead Seabream (Sparus aurata L.)

The use of natural immunostimulants is considered the most promising alternative to promote fish health, productive performance and quality, increasing the aquaculture profitability, sustainability and social acceptance. The purpose of this study was to evaluate the effect of the integration of a potential probiotic strain, Halobacterium salinarum, belonging to the Archaea domain, in the formulated diets of farmed gilthead seabream (Sparus aurata L.) in terms of growth performances and immunity responses. The experiment was set up to test two different levels of inclusion of the bacteria in the diet: 0.05% (D1) and 0.1% (D2). The effects on fish growth performances; humoral (peroxidase, protease, antiprotease and IgM levels) and cellular immunity parameters (phagocytosis, respiratory burst and myeloperoxidase), along with bactericidal activity, were evaluated after 15 and 30 days of experimental feeding. The obtained results showed that the inclusion of H. salinarum at the highest concentration (D2 0.1%) improved growth performances, bactericidal activity against Vibrio anguillarum and some parameters related both to the humoral and cellular immune response, suggesting exploring other aspects of welfare in view of future supplementations of this probiotic strain in the diet of S. aurata.

Evaluation of Bacillus spp. as Potent Probiotics with Reduction in AHPND-Related Mortality and Facilitating Growth Performance of Pacific White Shrimp (Litopenaeus vannamei) Farms

Acute hepatopancreatic necrosis disease (AHPND) is a serious bacterial disease affecting shrimp aquaculture worldwide. In this study, natural microbes were used in disease prevention and control. Probiotics derived from Bacillus spp. were isolated from the stomachs of AHPND-surviving Pacific white shrimp Litopenaeus vannamei (22 isolates) and mangrove forest soil near the shrimp farms (10 isolates). Bacillus spp. were genetically identified and characterized based on the availability of antimicrobial peptide (AMP)-related genes. The phenotypic characterization of all Bacillus spp. was determined based on their capability to inhibit AHPND-causing strains of Vibrio parahaemolyticus (VPAHPND). The results showed that Bacillus spp. without AMP-related genes were incapable of inhibiting VPAHPND in vitro, while other Bacillus spp. harboring at least two AMP-related genes exhibited diverse inhibition activities. Interestingly, K3 [B. subtilis (srfAA+ and bacA+)], isolated from shrimp, exerted remarkable inhibition against VPAHPND (80% survival) in Pacific white shrimp and maintained a reduction in shrimp mortality within different ranges of salinity (75-95% survival). Moreover, with different strains of VPAHPND, B. subtilis (K3) showed outstanding protection, and the survival rate of shrimp remained stable among the tested groups (80-95% survival). Thus, B. subtilis (K3) was further used to determine its efficiency in shrimp farms in different locations of Vietnam. Lower disease occurrences (2 ponds out of 30 ponds) and greater production efficiency were noticeable in the B. subtilis (K3)-treated farms. Taking the results of this study together, the heat-shock isolation and genotypic-phenotypic characterization of Bacillus spp. enable the selection of probiotics that control AHPND in Pacific white shrimp. Consequently, greater disease prevention and growth performance were affirmed to be beneficial in the use of these probiotics in shrimp cultivation, which will sustain shrimp aquaculture and be environmentally friendly.

Weissella confusa N17 Derived from Loach (Misgurnus anguillicaudatus) Exhibits Promising for Further Applications in Loach Aquaculture

The application of probiotics, in aquaculture, is becoming increasingly widespread and have had positive application effects. However, reports of loach-derived probiotics are quite limited. In this study, two representative strains of lactic acid bacteria with excellent traits, namely, Weissella confusa N17 and Lactobacillus saniviri N19, were screened from the intestine of healthy loaches. W. confusa N17 and L. saniviri N19 could inhibit different common various pathogenic bacteria, especially Aeromonas spp., and were sensitive to the most common antibiotics. The survival rate of the two strains exceeded 50% after 4 h of incubation in 10% loach bile. Moreover, the two strains showed significant tolerance to trypsin. Their autoaggregation capacity and hydrophobicity were greater than 30%. In addition, the aggregation ability of both strains was higher than 30% for both A. veronii TH0426 and A. hydrophila TPS. The two strains had a high biofilm-forming ability and strong adhesion to epithelioma papulosum cyprini (EPC) cells. Scanning electron microscopy results showed that the culture supernatants of the two strains had a significantly destructive effect on A. veronii TH0426 and A. hydrophila TPS. Overall, the traits of W. confusa N17 were better than those of L. saniviri N19. Genome sequencing and analysis demonstrated a lack of virulence factor-related or drug resistance-related genes in genome N17. The diet supplemented with the W. confusa N17 strain significantly improved the resistance of loaches to A. veronii infection, and the protection rate reached 57.1%. Therefore, W. confusa N17 exhibits promising for further applications in loach aquaculture.

Characterization of Host-Associated Microbiota and Isolation of Antagonistic Bacteria from Greater Amberjack (Seriola dumerili, Risso, 1810) Larvae

Greater amberjack (Seriola dumerili) is a new species in marine aquaculture with high mortalities at the larval stages. The microbiota of amberjack larvae was analyzed using 16S rDNA sequencing in two groups, one added copepod nauplii (Acartia tonsa) in the diet, and one without copepods (control). In addition, antagonistic bacteria were isolated from amberjack larvae and live food cultures. Proteobacteria was the most abundant phylum followed by Bacteroidota in amberjack larvae. The composition and diversity of the microbiota were influenced by age, but not by diet. Microbial community richness and diversity significantly increased over time. Rhodobacteraceae was the most dominant family followed by Vibrionaceae, which showed the highest relative abundance in larvae from the control group 31 days after hatching. Alcaligenes and Thalassobius genera exhibited a significantly higher relative abundance in the copepod group. Sixty-two antagonistic bacterial strains were isolated and screened for their ability to inhibit four fish pathogens (Aeromonas veronii, Vibrio harveyi, V. anguillarum, V. alginolyticus) using a double-layer test. Phaeobacter gallaeciensis, Phaeobacter sp., Ruegeria sp., and Rhodobacter sp. isolated from larvae and Artemia sp. inhibited the fish pathogens. These antagonistic bacteria could be used as host-derived probiotics to improve the growth and survival of the greater amberjack larvae.

Current Status of Probiotics in European Sea Bass Aquaculture as One Important Mediterranean and Atlantic Commercial Species: A Review

European sea bass production has increased in recent decades. This increase is associated with an annually rising demand for sea bass, which encourages the aquaculture industries to increase their production to meet that demand. However, this intensification has repercussions on the animals, causing stress that is usually accompanied by dysbiosis, low feed-conversion rates, and immunodepression, among other factors. Therefore, the appearance of pathogenic diseases is common in these industries after immunodepression. Seeking to enhance animal welfare, researchers have focused on alternative approaches such as probiotic application. The use of probiotics in European sea bass production is presented as an ecological, safe, and viable alternative in addition to enhancing different host parameters such as growth performance, feed utilization, immunity, disease resistance, and fish survival against different pathogens through inclusion in fish diets through vectors and/or in water columns. Accordingly, the aim of this review is to present recent research findings on the application of probiotics in European sea bass aquaculture and their effect on growth performance, microbial diversity, enzyme production, immunity, disease resistance, and survival in order to help future research.

Fructooligosaccharide and Bacillus subtilis synbiotic combination promoted disease resistance, but not growth performance, is additive in fish

Species diversification from major to minor carps for their sturdiness and initial higher growth, and also a quest for antibiotic-free aqua farming in the subcontinent, mandates search for and evaluation of alternatives. An experiment was performed to investigate the potential of fructooligosaccharide (FOS) and Bacillus subtilis (BS) (alone or as synbiotics) in promoting growth and immunity against infections in Labeo fimbriatus fingerlings. Six iso-nitrogenous and iso-lipidic diets containing combinations of two levels of FOS (0% and 0.5%) and three levels of BS (0, 104, 106 CFU/g feed) were fed to fish for 60 days. At the end of the feeding trial, twenty-four fish from each group were injected intra-peritoneally with pathogenic strain of Aeromonas hydrophila O:18 to test the immunoprotective efficacy of the supplements against bacterial infection. BS, but not FOS, significantly improved (P < 0.05) growth and feed utilisation attributes like percentage weight gain (PWG), specific growth rate (SGR) and feed conversion ratio (FCR). There were interactive effects of FOS and BS on PWG, SGR and FCR; however, the effects were not additive in nature. These beneficial effects of BS, alone or in combination with FOS, were corroborated by increased protease activity, microvilli density and diameter and number of goblet cells. Overall beneficial effects of FOS and BS included improved erythrocyte (RBC), hemoglobin (Hb), total protein and globulin levels. Total leucocyte (WBC) count and immunological parameters like respiratory burst activity of leucocytes (NBT reduction), lysozyme activity, albumin: globulin ratio and post-challenge survival were significantly improved by both FOS and BS, and their dietary combination yielded the highest improvement in these parameters. Synergistic effects of FOS and BS as dietary supplements indicate that a combination of 106 CFU/g BS and 0.5% FOS is optimal to improve growth, feed utilisation, immune functions, and disease resistance in L. fimbriatus fingerlings.

The stability and composition of the gut and skin microbiota of Atlantic salmon throughout the yolk sac stage

The bacterial colonization of newly hatched fish is important for the larval development and health. Still, little is known about the ontogeny of the early microbiota of fish. Here, we conducted two independent experiments with yolk sac fry of Atlantic salmon that were (1) either reared conventionally, with the eggs as the only source for bacteria (egg-derived microbiota; EDM) or (2) hatched germ-free and re-colonized using lake water (lake-derived microbiota; LDM). First, we characterized the gut and skin microbiota at 6, 9, and 13 weeks post hatching based on extracted RNA. In the second experiment, we exposed fry to high doses of either a fish pathogen or a commensal bacterial isolate and sampled the microbiota based on extracted DNA. The fish microbiota differed strongly between EDM and LDM treatments. The phyla Proteobacteria, Bacteroidetes, and Actinobacteria dominated the fry microbiota, which was found temporarily dynamic. Interestingly, the microbiota of EDM fry was more stable, both between replicate rearing flasks, and over time. Although similar, the skin and gut microbiota started to differentiate during the yolk sac stage, several weeks before the yolk was consumed. Addition of high doses of bacterial isolates to fish flasks had only minor effects on the microbiota.