A review on the application of Bacillus as probiotics in aquaculture

Bacillus subtilis HGCC-1 improves growth performance and liver health via regulating gut microbiota in golden pompano

Probiotics as green inputs have been reported to regulate metabolism and immunity of fish. However, the mechanisms by which probiotics improve growth and health of fish are unclear. Therefore, the aim of this study was to investigate the effect of Bacillus subtilis HGCC-1, an indigenous probiotic isolated from fish, on growth performance, host lipid metabolism, liver inflammation and gut microbiota of golden pompano. 160,000 golden pompanos with the initial body weight of 93.6 ± 5.0 g was randomly assigned to two dietary groups: Control and HGCC-1 (control diet supplemented with 0.3 g/kg Bacillus subtilis HGCC-1 fermentation product), and after three weeks of feeding, 26 golden pompanos were randomly collected from each group for gut microbiome and host phenotype analysis. Dietary supplementation with Bacillus subtilis HGCC-1 significantly promoted growth performance (P < 0.05) and enhanced feed utilization. Besides, HGCC-1 improved liver health and alleviated hepatic steatosis and inflammation. Furthermore, Bacillus subtilis HGCC-1 enhanced intestinal lipid absorption, promoted hepatic utilization of dietary fat by improving hepatic lipid uptake/transport and fatty acid β-oxidation to provide energy, and reduced hepatic TG level (P < 0.05), which may be the potential mechanism of Bacillus subtilis HGCC-1-mediated growth promotion. Finally, Bacillus subtilis HGCC-1 significantly altered the structure and function of gut microbiota (P < 0.05), leading to enrichment of beneficial taxa such as Bacillus (P < 0.0001) and increased of the ratio of "Functional Group 2/Functional Group 1" (P = 0.00092). Interestingly, the ratio of "Functional Group 2/Functional Group 1" was linked to the growth traits (Spearman, P < 0.05), while the intestinal abundance of Bacillus was correlated with serum TG in fish (Spearman, R = 0.47, P = 0.00091), suggesting a role of the intestinal microbiota in HGCC-1 mediated effect on growth and lipid metabolism. In summary, Bacillus subtilis HGCC-1 promotes growth performance, alleviate hepatic steatosis and enhances liver health via regulating gut microbiota in golden pompano, which ultimately showed as beneficial effect of fish growth and health.

Impact of essential oil and probiotics supplementation on growth performance, serum biomarkers, antioxidants status, bioenergetics and histomorphometry of intestine of Nile tilapia fingerlings challenged with Aeromonas veronii

BACKGROUND

Probiotics and essential oils feed supplements are widely used in the aquaculture sector. This study was conducted to evaluate the effects of dietary supplementation with probiotics, essential oils and their combination on growth performance, serum biochemical parameters, antioxidant capacity, resistance against Aeromonas veronii, and intestinal histomorphology of Nile tilapia (Oreochromis niloticus). A total of 360 O. niloticus fingerlings were randomly assigned to four groups (3 replicates/ group; each replicate contains 30 fish) based on the different dietary treatments. The first group was fed a basal control diet (G1), the second group was fed a basal diet supplemented with 0.015% probiotic (Klu-zetar®) (G2), the third group was fed a basal diet with 0.015% essential oil (ACTIVO®) (G3), and the fourth group was fed a basal diet mixed with 0.015% Klu-zetar® and 0.015% ACTIVO®, (G4) for 6 weeks. At the end of the trial fish were intraperitoneally injected with pathogenic bacteria Aeromonas veronii and the fish mortality rate was recorded for 7 days post infection.

RESULTS

The results revealed that using probiotics and or essential oils in Nile tilapia diets improved growth performance, reduced oxidative stress, enhanced immunity, maintained intestinal integrity, and enhanced resistance to pathogenic infection (P ≤ 0.05).

CONCLUSIONS

It is concluded that the use of probiotics and/ or essential oils enhance the overall outcomes of Nile tilapia, so it is highly recommended to be used in aquaculture management.

Effects of dietary inclusion of Bacillus amyloliquefaciens AV5 on growth performance, antioxidant activity, innate immune, and hematological responses in Nile tilapia (Oreochromis niloticus) reared at low and high stocking densities

This research work investigated the efficacy of Bacillus amyloliquefaciens AV5 in mitigating the stress effects of stocking densities in Nile tilapia (Oreochromis niloticus). 520 healthy Nile tilapia fingerlings (24.43 ± 1.4g) were randomly allocated to 16 plastic tanks, each with a capacity of 400L. Two stocking densities were tested: low density (37.5 fish/m³) and high density (125 fish/m³) with four treatment groups(low density with a control diet (LDC), high density with a control diet (HDC), low density with a supplemented diet (LDS), and high density with a supplemented diet (HDS)) for 8 weeks. HDC exhibited lower values (P < 0.05) for specific growth rate, final weight, weight gain rate, and specific growth rate than fish fed at LDC, LDS, and HDS. The lowest feed conversion ratio was recorded at the LDS and HDS. There were no significant differences (P > 0.05) in survival rates among treatments. There were no notable disparities (P > 0.05) in the LDC, LDS, and HDS body composition. Antioxidant enzyme activities were greater in LDC, LDS, and HDS than in HDC, while malondialdehyde levels were higher in HDC, and hematology parameters in HDS were improved compared to HDC. Elevated levels (P < 0.05) of phagocytic and lysozyme activity were seen in LDS and HDS. There was no change in glucose levels in HDS and LDC. Nonetheless, cortisol was elevated in HDC compared to LDC, LDS, and HDS. Hence, B. amyloliquefaciens AV5(1 × 108 cfu/g) is a potential probiotic to alleviate HDC-induced stress in O. niloticus.

Isolation, characterization of Bacillus subtilis and Bacillus amyloliquefaciens and validation of the potential probiotic efficacy on growth, immunity, and gut microbiota in hybrid sturgeon (Acipenser baerii ♀ × Acipenser schrenckii ♂)

Probiotics are increasingly considered as an alternative to antibiotics in developing environmentally sustainable aquaculture practices. Hybrid sturgeon (Acipenser baerii ♀ × Acipenser schrenckii ♂), a globally popular species valued for its nutritional content and caviar, has limited research on host-associated probiotics. In this study, we isolated and identified Bacillus subtilis and Bacillus amyloliquefaciens from healthy hybrid sturgeon and assessed their impact on growth, immunity, gut microbiota, and transcriptome following an 8-week feeding trial. The isolated strains demonstrated strong production of protease, amylase, lipase, and cellulase, along with broad-spectrum pathogen inhibition, including Aeromonas veronii, Aeromonas sobria, and Yersinia ruckeri. Supplementation with B. subtilis and B. amyloliquefaciens significantly improved growth performance and increased survival rates against A. veronii infection. Mechanistically, probiotics altered gut microbiota composition, enhancing digestive functions. Transcriptome analysis further revealed that probiotic supplementation boosted immune response and protein digestion and absorption. These findings suggest that B. subtilis and B. amyloliquefaciens are promising probiotic candidates for the hybrid sturgeon industry, offering effective protection against A. veronii infection.

Microbiological contamination of lettuce (Lactuca sativa) reared with tilapia in aquaponic systems and use of bacillus strains as probiotics to prevent diseases: A systematic review

Aquaponic systems are food production systems that combine aquaculture and hydroponic in a closed recirculation system where water provides nutrients to plants while plants purify water for fish. In this system, tilapia is the most commonly cultured fish and can be easily integrated with vegetable cultivation. However, tilapia host a diverse microbiota some of which are pathogenic and can infect humans. Previous studies have reported contamination of lettuce by pathogenic bacteria which can cause human diseases. Thus, there is an urgent need to employ effective methods to control those bacteria, and Bacillus strains have been successfully used in this context. This systematic review aimed to provide a comprehensive overview of lettuce contamination by pathogenic bacteria and the use of Bacillus as probiotics to prevent diseases in aquaponics systems. This systematic review was performed using Preferred Reporting Items for Systematic Review and Meta-Analysis Statement (PRISMA) Guidelines. A total of 1,239 articles were retrieved and based on eligibility criteria, six articles were included after screening. The review revealed that Enterobacteriaceae, Coliforms, and Shiga Toxin-producing E. coli are the predominant bacteria contaminating lettuce leaves in Aquaponic systems, and Shiga Toxin-Producing E. coli can internalize in the lettuce leaves, putting public health at risk. The included studies did not report the presence of V. cholerae in lettuce grown in aquaponic systems, and the use of Bacillus as probiotics to control Escherichia coli and Vibrio Cholerae. Further research is needed to explore the potential of tilapia to act as a source of pathogenic bacteria that can contaminate lettuce, as well as to investigate the effectiveness of Bacillus strains as probiotics to control these bacteria and ensure food safety.

Impact of probiotic Bacillus sp. dietary supplementation on pancreatic and intestinal activities in seabream Sparus aurata

The main objective of this study was to investigate the effects of commercial probiotic Bacillus sp. supplementation on seabream Sparus aurata larviculture under culture conditions. In this context, Bacillus was supplemented via rotifer feeding and water and its effects on pancreatic and intestinal enzyme activities as well as aquaculture parameters were evaluated during early life development. In the experimental group, as probiotic three Bacillus sp. spores were introduced via rotifer and larval culture tanks, while the larvae in control group did not feed any probiotic supplementation. At the end of the experiment on 40 days after hatching, the probiotic-supplemented group exhibited better growth performance and there were statistically differences in between groups of probiotic-treated and control regarding growth parameters (P < 0.01), despite insignificant survival rate (P > 0.05). In terms of enzymatic expressions, S. aurata larvae receiving probiotic supplementation through rotifers demonstrated noteworthy (P < 0.05) enhancements in specific activities of pancreatic and intestinal enzymes, except for amylase (P > 0.05), when compared to the control group. It is concluded that the administration of Bacillus sp. as probiotic bacteria through rotifer supplementation and water intake demonstrates significant positive impacts on both growth parameters and specific activities of main pancreatic and intestinal enzymes of seabream larvae.

Recombinant Bacillus subtilis expressing functional peptide and its effect on blunt snout bream (Megalobrama amblycephala) in two state of stress

This study was conducted to investigate the effects of recombinant Bacillus subtilis CM66-P4' (secreting P4, which related to previous research in this laboratory) on the antioxidant capacity and immune function of blunt snout bream (Megalobrama amblycephala) through in vitro and in vivo experiment. The culture experiment was divided into 3 groups, including control group (CG, with no additional bacteria), original bacteria group (OBG, with 2 × 109 CFU/kg Bacillus subtilis CM66) and recombinant bacteria group (RBG, with 2 × 109 CFU/kg Bacillus subtilis CM66-P4'). After 8 weeks of feeding, a part of the fish were subjected to fishing stress, and the rest were subjected to starvation stress test. Blood samples were collected for the determination of immune and stress-related indexes. The hepatocytes were divided into control group (CG) and experiment group with P4 peptide (LTG and HTG). The cells were collected after starvation treatment and the expression of related genes was detected. The results showed as follows: compared with the CG group, the gene expressions of hepatocytic hsp60 and hsp70 in the LTG and HTG groups were significantly suppressed after 24 h starvation stress (P < 0.05). The content of MDA, the activities of AKP and ALT in OBG group were significantly changed after 30 days starvation (P < 0.05), while the indexes in RBG group had no significant change. The changes of plasma cortisol, malondialdehyde (MDA) and Immunoglobulin M (IgM) in CG and OBG groups were significantly changed at 4 h after fishing stress (P < 0.05), while the indexes in RBG group was not. In conclusion, this study confirmed that Bacillus subtilis CM66-P4' has great potential in preventing adverse effects of stress on aquatic livestock.

Antifungal Activity of Rhizosphere Bacillus Isolated from Ziziphus jujuba Against Alternaria alternata

The serious impact of Alternaria alternata on jujube black spot disease has seriously affected the quality and yield of jujube, constraining the sustainable development of the jujube industry. The purpose of this study was to isolate and screen highly effective biocontrol strains of jujube black spot disease from jujube rhizosphere soil. Thirty-three soil samples were collected from four regions in southern Xinjiang. The strains with antagonistic effects were isolated and screened by the dilution spread method and plate confrontation method and identified by morphological, physiological, and biochemical characteristics, as well as 16S rDNA, gyrB, and rpoB gene sequences. Indoor and field efficacy experiments were conducted to determine their biocontrol effect. A total of 110 strains with antibacterial activity were selected, and one strain, Bacillus velezensis 26-8, with a stable antagonistic effect was further tested. Biological characteristic experiments showed that strain 26-8 could grow at NaCl concentrations of 0.5-10% and pH 4.0-9.0. The biocontrol experiment results showed that Bacillus velezensis 26-8 could achieve an 89.83% control effect against black spot disease. In conclusion, strain 26-8 has good salt and alkali tolerance, exerts a good control effect on jujube black spot disease, and is worthy of further study.

Dietary administration of Bacillus amyloliquefaciens AV5 on antioxidant activity, blood parameters, and stress responses of Nile tilapia (Oreochromis niloticus) raised under hypoxia and temperature variability

The ability of Nile tilapia to tolerate hypoxia, as well as low and high temperatures, presents a significant economic concern, as it adversely affects their growth and leads to increased mortality rates. A 42-day feeding trial was conducted to evaluate the impact of adding Bacillus amyloliquefaciens AV5 to a fish meal on the physiological response of Nile tilapia. Three meals were administered to fish (23.4 ± 0.3g) in triplicates. The diets included GC (without B. amyloliquefaciens AV5), G1 (106 cfu/g), and G2 (108 cfu/g). After the treatment trial, we assessed the antioxidant parameters, hemato-immunological indices, and stress-related genes in O. niloticus. Subsequently, we subjected the fish to hypoxia for 20h and low and high temperatures for 3h each. The findings demonstrated a significant rise in white blood cells, red blood cells, haemoglobin, and hematocrit levels in the blood of fish that were fed a meal supplemented with B. amyloliquefaciens AV5, compared to the control group (GC) (P<0.05), the serum of all fish groups that were supplemented with B. amyloliquefaciens AV5 exhibited an increase in catalase, total antioxidant capacity and superoxide dismutase activity and a decrease in lactate dehydrogenase, alanine aminotransferase, aspartate aminotransferase, pyruvate kinase, myeloperoxidase, glucose, cortisol (P < 0.05). In addition, all fish diet groups that received B. amyloliquefaciens AV5 as a supplement exhibited elevated levels of HIF-1α and HSP70 expression in their livers (P<0.05). Nile tilapia in the G2 diet, exhibited improved values in most evaluated indices under various stress settings (P<0.05). These data indicate that the G2 supplement may be used as a preventive measure to weaken the impacts of environmental stress on O. niloticus.

Preliminary investigation on the effect of Vibrio splendidus stimulation on the intestinal flora of Strongylocentrotus intermedius

To better understand the effect of Vibrio splendidus infection on Strongylocentrotus intermedius, 16S rRNA sequencing was carried out to investigate the intestinal flora of S. intermedius stimulated by 0 CFU/mL (Con), 1.5 × 107 CFU/mL (Vib1) and 1.5 × 108 CFU/mL (Vib2) concentrations of V. splendidus. The results showed that there was significant difference in intestinal flora diversity between Con group and Vib1 group, but no significant difference between Con group and Vib2 group. However, there were significant differences in the composition of intestinal flora among all groups. Bacteroidota, Proteobacteria and Firmicutes were the dominant phylum in the Con group. The abundance of Bacteroidota and Firmicutes decreased and Proteobacteria increased in Vib1 and Vib2 groups. The relative abundance of the potential probiotic bacteria Muribaculaceae and Alloprevotella was significantly lower in the Vib1 and Vib2 groups. In addition, the opportunistic pathogen Desulfovibrio was found in Vib1 and Vib2 groups. It is evident that V. splendidus infection not only alters the composition of the microbial community in the intestinal tract of S. intermedius, but may also lead to the production of opportunistic pathogens, which could be potentially harmful to the health of S. intermedius. The results of this study provide a foundation for exploring the diseases caused by V. splendidus stimulation leading to an imbalance in the intestinal flora of S. intermedius, and contribute to our further understanding of the role of Vibrio on the health of S. intermedius.

Characterization and comparative genomic analysis of a marine Bacillus phage reveal a novel viral genus

Bacillus pumilus exhibits substantial economic significance, with its metabolism, adaptability, and ecological functions regulated by its bacteriophages. Here, we isolated and characterized a novel temperate phage vB_BpuM-ZY1 from B. pumilus derived from mangrove sediments by mitomycin C induction. Phage vB_BpuM-ZY1 is a typical myophage, which has an icosahedral head with a diameter of 43.34 ± 2.14 nm and a long contractible tail with a length of 238.58 ± 5.18 nm. Genomic analysis indicated that vB_BpuM-ZY1 encodes genes for lysogeny control, and its life cycle may be intricately regulated by multiple mechanisms. vB_BpuM-ZY1 was predicted to employ P2-like 5'-extended-cos packaging strategy. In addition, genome-wide phylogenetic tree and proteome tree analyses indicated that vB_BpuM-ZY1 belongs to the Peduoviridae family but forms a separate branch at a deeper taxonomic level. Particularly, the comparative genomic analysis showed that vB_BpuM-ZY1 has less than 70% intergenomic similarities with its most similar phages. Thus, we propose that vB_BpuM-ZY1 is a novel Bacillus phage belonging to a new genus under the Peduoviridae family. The protein-sharing network analysis identified 44 vB_BpuM-ZY1-related phages. Interestingly, these evolutionarily related myophages infect a broad range of hosts across different phyla, which may be explained by the high structural variations of the host recognition domain in their central spike proteins. Collectively, our study will contribute to our understanding of Bacillus phage diversity and Bacillus-phage interactions, as well as provide essential knowledge for the industrial application of B. pumilus.

IMPORTANCE

Although recent metagenomics research has obtained a wealth of phage genetic information, much of it is considered "dark matter" because of the lack of similarity with known sequences in the database. Therefore, the isolation and characterization of novel phages will help to interpret the vast unknown viral metagenome data and improve our understanding of phage diversity and phage-host interactions. Bacillus pumilus shows high economic relevance due to its wide applications in biotechnology, industry, biopharma, and environmental sectors. Since phages influence the abundance, metabolism, evolution, fitness, and ecological functions of bacteria through complex interactions, the significance of isolation and characterization of novel phages infecting B. pumilus is apparent. In this study, we isolated and characterized a B. pumilus phage belonging to a novel viral genus, which provides essential knowledge for phage biology as well as the industrial application of B. pumilus.

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.

Host Gut-Derived Probiotic, Exiguobacterium acetylicum G1-33, Improves Growth, Immunity, and Resistance to Vibrio harveyi in Hybrid Grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂)

Several exogenous probiotics are applicable in fish culture; however, challenges in isolation and verification have hindered the full utilization of numerous host probiotics. Therefore, this study aimed to apply the host probiotic Exiguobacterium acetylicum G1-33 to hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂) cultures and explore its mechanism of action. In total, 360 hybrid grouper were divided into four groups, which were fed the following for 60 days: three received commercial feed with varying concentrations of E. acetylicum G1-33 (106, 108, and 1010 CFU/g), while a control group received commercial feed. The results showed that supplementation with 106 and 108 CFU/g of E. acetylicum G1-33 enhanced gut morphology, upregulated growth-related genes (ghr1, igf-2, s6k1, tor), and promoted growth, with supplementation with 108 CFU/g resulting in the most notable enhancement. However, supplementation with 1010 CFU/g inhibited growth, possibly because of changes in intestinal morphology. Additionally, supplementation with E. acetylicum G1-33 upregulated the expression of immune-related genes (c3, myd88, Cu/Zn-sod, tlr3, and tnf2) in the liver and head kidney but led to an increase in malondialdehyde content, as well as a decrease in alkaline phosphatase and acid phosphatase activities, in the liver and serum, indicating increased oxidative stress. Moreover, supplementation with 106 and 108 CFU/g E. acetylicum G1-33 enhanced the widespread expression of immune-related genes in the head kidney and liver, respectively, and improved resistance to Vibrio harveyi, whereas supplementation with 1010 CFU/g weakened this resistance. In conclusion, E. acetylicum G1-33, particularly at 108 CFU/g, emerged as an effective probiotic, optimizing growth performance and immunity in hybrid grouper. This research is pioneering in its application of E. acetylicum in mariculture, potentially broadening the range of probiotic strategies in aquaculture.

Bacillus spp. Isolated from Miang as Potential Probiotics in Nile Tilapia Culture-In Vitro Research

Among 79 Bacillus spp. isolated from Miang, a fermented tea in north Thailand, 17 Bacillus strains were selected with probiotic potential in Nile tilapia culture based on the capabilities of bacteriocin production and associated antimicrobial activities against fish pathogens, Aeromonas hydrophila and Streptococcus agalactiae. However, only six isolates were selected for further extensive studies based on the strength of their antimicrobial activities and their tolerance against simulated gastrointestinal conditions. The molecular identification by 16S rRNA gene sequence analysis revealed that five isolates, K2.1, K6.1, K7.1, K15.4, and K22.6, were Bacillus tequilensis, and the isolate K29.2 was Bacillus siamensis. B. siamensis K29.2 showed complete susceptibility to antibiotics tested in this study, while B. tequilensis K 15.4 showed moderate resistance to some antibiotics; therefore, both strains were selected as potential probiotic bacteria. B. tequilensis K15.4 and B. siamensis K29.2 were capable of the production and secretion of extracellular protease and polysaccharide degrading enzymes, including cellulase, xylanase, and β-mannanase. The tannin tolerant test also demonstrated their ability to grow on selective agar plates and secrete cellulase and β-mannanase in the presence of hydrolyzable tannin. In addition, in vitro digestion of commercial fish substrate revealed that the extracellular enzymes produced by both strains efficiently reacted with feed protein and polysaccharides. Based on the results from this study, B. siamensis K29.2 was deemed to have the highest potential multifunctional probiotic qualities for application in Nile tilapia culture, while the antibiotic-resistant gene in B. tequilensis K15.4 must be clarified before field application.

Dietary Effects of Probiotic Bacteria, Bacillus amyloliquefaciens AV5 on Growth, Serum and Mucus Immune Response, Metabolomics, and Lipid Metabolism in Nile Tilapia (Oreochromis niloticus)

In the present study, we investigated the effect of dietary supplementation with the probiotic Bacillus amyloliquefaciens AV5 (OR647358) on the growth, serum and mucus immune responses, metabolomics, and lipid metabolism of Oreochromis niloticus. Fishes (27.2 ± 1.7 g and 9.0 ± 1.2 cm) were fed three distinct meals: a commercial diet (control-GC) and two treatment diets supplemented with probiotics at 106 (G1) and 108 cfu/g (G2), respectively, for 30 days. In the G2 group, the final weight, specific growth rate, weight gain rate, survival rate, and feed conversion ratio of the fish were significantly improved (p < 0.05). Lysozyme, myeloperoxidase, and alkaline phosphatase activities in the mucus of fish were significantly higher (p < 0.05) in the G1 and G2 groups. The serum total protein, superoxide dismutase, glutathione peroxidase, reactive oxygen species, and reactive nitrogen species levels were noticeably higher (p < 0.05) in fish fed G1 and G2. In addition, in the G1 and G2 groups, higher levels of enzymes involved in lipid metabolism, such as pyruvate kinase, 2-hydroxyethyl-ThPP, and dihydrolipoamide dehydrogenase, were increased. Distal gastrointestinal metabolites, such as glycerophospholipids and histidine, were observed. These findings strongly indicate that incorporating B. amyloliquefaciens AV5 at 108 cfu/g into commercial feeds positively influences fish growth, immunity, and lipid metabolism.

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.

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.

Probiotic Efficacy in Aquaculture: The Role of Technospore® (Bacillus coagulans) in Improving Nile Tilapia (Oreochromis niloticus) Performance and Disease Resistance: a Study on Gut Health, Immunological Response, and Gene Expression

This study evaluated the effects of Technospore® (Bacillus coagulans) supplementation on intestinal health, immune response, and Oreochromis niloticus (Nile tilapia) growth performance. The experiment divided fish into four groups: a control group fed an unsupplemented diet and three experimental groups receiving diets supplemented with 0.2 g/kg, 0.4 g/kg, and 0.8 g/kg of Technospore®, respectively. Results indicated that Technospore® supplementation significantly enhanced growth rates and feed efficiency in all treated groups, with the most pronounced improvements observed in the group receiving 0.4 g/kg. Furthermore, the study revealed that B. coagulans supplementation markedly boosted serum immune responses, as evidenced by increased phagocytic activity, phagocytic index, and lysozyme levels, following a challenge with Aeromonas hydrophila. Histological analysis showed improved gut morphology, while gene expression analysis indicated upregulation of immune-related genes, including liver IGF-1, GHR, HSP70, IL-1β, and TNF-α, as well as spleen TNF-α and IL-1β and intestinal C-lysozyme and TNF-α, both before and after the bacterial challenge. These findings suggest that dietary inclusion of Technospore® can significantly improve gut health and immune responses in tilapia, potentially serving as an effective prophylactic alternative to antibiotics in aquaculture.

Influence of stocking density on the growth, immune and physiological responses, and cultivation environment of white-leg shrimp (Litopenaeus vannamei) in biofloc systems

Biofloc (BF) stands out as a promising system for sustainable shrimp farming. Optimizing various culture conditions, such as stocking density, carbohydrate source, and feeding management, is crucial for the widespread adoption of the BF system. This study compares the growth performance of white-leg shrimp (Litopenaeus vannamei) in culture ponds at low density (LD) with 50 organisms/m2 and high density (HD) with 200 organisms/m2. Post-larvae of white-leg shrimp were stocked for 16 weeks in both LD and HD groups. The LD group exhibited a superior survival rate, growth rate, and feed consumption compared to the HD group. The BF from the LD system recorded a significantly higher protein content (16.63 ± 0.21%) than the HD group (15.21 ± 0.34%). Heterotrophic bacterial counts in water did not significantly differ with stocking density. However, Vibrio count in water samples was higher in the HD group (3.59 ± 0.35 log CFU/mL) compared to the LD group (2.45 ± 0.43 log CFU/mL). The whole shrimp body analysis revealed significantly higher protein and lipid content in the LD group. In contrast, the total aerobic bacterial count in shrimp from the HD group was high, with the identification of Salmonella enterica ssp. arizonae. Additionally, Vibrio counts in shrimp samples were significantly higher in the HD group (4.63 ± 0.32 log CFU/g) compared to the LD group (3.57 ± 0.22 log CFU/g). The expression levels of immune-associated genes, including prophenoloxidase, transglutaminase, penaiedin 3, superoxide dismutase, lysozyme, serine proteinase, and the growth-related gene ras-related protein (rap-2a), were significantly enhanced in the LD group. Conversely, stress-related gene expression increased significantly in the HD group. Hepatopancreases amylase, lipase, and protease were higher in the LD group, while trypsin activity did not differ significantly. Antioxidant enzyme activity (catalase, glutathione, glutathione peroxidase, and superoxide dismutase) significantly increased in the LD group. The histological structure of hepatopancreas, musculature, and female gonads remained similar in both densities. However, negative effects were observed in the gills' histology of the HD group. These results suggest that increasing stocking density is associated with significantly negative biological, microbial, and physiological effects on white-leg shrimp under the BF system.

Streptococcus iniae in aquaculture: a review of pathogenesis, virulence, and antibiotic resistance

One of the main challenges in aquaculture is pathogenic bacterial control. Streptococcus iniae stands out for its ability to cause high mortality rates in populations of commercially important fish populations and its recent recognition as an emerging zoonotic pathogen. The rise in identifying over 80 strains some displaying antibiotic resistance coupled with the emerging occurrence of infections in marine mammal species and wild fish underscores the urgent need of understanding pathogenesis, virulence and drug resistance mechanisms of this bacterium. This understanding is crucial to ensure effective control strategies. In this context, the present review conducts a bibliometric analysis to examine research trends related to S. iniae, extending into the mechanisms of infection, virulence, drug resistance and control strategies, whose relevance is highlighted on vaccines and probiotics to strengthen the host immune system. Despite the advances in this field, the need for developing more efficient identification methods is evident, since they constitute the basis for accurate diagnosis and treatment.

The effects of Bacillus subtilis on the immunity, mucosal tissue morphology, immune-related gene transcriptions, and intestinal microbiota in flounder (Paralichthys olivaceus) with two feeding methods: Continuous versus discontinuous feeding

Probiotics as dietary additives can improve weight gain, feed efficiency, and disease resistance in cultured fish. In this research, we evaluated and compared the effects of Bacillus subtilis on immunity, mucosal tissue morphology, immune-related gene transcriptions, and intestinal microbiota in flounder (Paralichthys olivaceus) by a 30-day feeding experiment based on a continuous feeding schedule (E1) and a discontinuous feeding schedule (E2). As a result, the use of B. subtilis exerted the best positive effects on survival rate, enzyme activity, mucosal tissue morphology, immune-related gene transcriptions, and intestinal microbiota in flounders. Alkaline phosphatase (AKP), lysozyme (LZM), and superoxide dismutase (SOD) activities in the liver of E2 were higher than those of E1 (P < 0.05). Furthermore, the villi length in the intestinal tract and the fold length in the stomach of E2 were also higher than in E1 (P < 0.05). The il-1 expression levels in the spleen were significantly increased in E2 (P < 0.05) compared to E1. We performed 16 S rRNA sequencing analysis to find that Bacillus in E1 (1.06%) and E2 (1.01%) had higher relative abundances than in E0 (0.053%) at the end of the experiments, indicating that short-term application of B. subtilis with the continuous or discontinuous feeding method can allow both the adaptation of the ecosystem to the presence of probiotics by the establishment of new species in the gut microbiota and the ability these new probiotic species to perform corresponding functions. No significant differences in the ability of probiotic establishment were observed between E1 and E2. Our findings provided a unique perspective to explore the mechanism of immune enhancement with probiotics and to screen the optimal administration strategy in aquaculture application for probiotic use. Together, these results point to some level of enhancement in immune status by continuous and discontinuous feeding after a short-term feeding period, which could be used as a prophylactic strategy for flounder health management.

Optimization of degradation conditions and analysis of degradation mechanism for nitrite by Bacillus aryabhattai 47

Excessive nitrite levels cause significant damage to aquaculture, making it crucial to explore green and reliable nitrite removal technologies. In this study, A Bacillus aryabhattai (designated as the strain 47) isolated from aquaculture wastewater was used as the experimental strain. The nitrite degradation conditions of the strain 47 were optimized, and the optimal conditions are: glucose was 12.74 g/L, fermented special soybean meal was 21.27 g/L, MgCl2 369 mg/L, pH 7.0, incubated at 30 °C with the inoculum size of 2 % and the rotation speed of 170 rpm. Under the optimal conditions, the nitrite concentration of the culture solution was 200 mg/L, and the nitrite removal rate reached 91.4 %. Meanwhile, the mechanism by which Mg2+ enhanced the nitrite degradation ability of the strain 47 was investigated by transcriptomics. An operon structure directed cellular trafficking of Mg2+, and then, the Mg2+-mediated catalytic reaction of multiple enzymes enhanced and improved cellular metabolic processes (e.g. the transport and metabolism of nitrite, central carbohydrate metabolism oxidative phosphorylation). At the same time, with the progress of cell metabolism, cells secreted a series of enzymes related to nitrite transport and metabolism to promote the metabolism of nitrite. And the process of the assimilated nitrate reduction pathway of nitrite degradation in the strain 47 was elaborated at the transcriptome level. This study provided a new insight into nitrite treatment mediated by microbial organisms.

Isolation and characterization of an antimicrobial Bacillus subtilis strain O-741 against Vibrio parahaemolyticus

Vibrio parahaemolyticus is a marine bacterium that can infect and cause the death of aquatic organisms. V. parahaemolyticus can also cause human foodborne infection via contaminated seafood, with clinical syndromes which include diarrhea, abdominal cramps, nausea and so on. Since controlling V. parahaemolyticus is important for aquaculture and human health, various strategies have been explored. This study investigates the application of antagonistic microorganisms to inhibit the growth of V. parahaemolyticus. We screened aquaculture environment samples and identified a Bacillus subtilis strain O-741 with potent antimicrobial activities. This strain showed a broad spectrum of antagonistic activities against V. parahaemolyticus and other Vibrio species. Application of the O-741 bacterium significantly increased the survival of Artemia nauplii which were infected with V. parahaemolyticus. Furthermore, the cell-free supernatant (CFS) of O-741 bacterium exhibited inhibitory ability against V. parahaemolyticus, and its activity was stable to heat, acidity, UV, enzymes, and organic solvents. Next, the O-741 CFS was extracted by ethyl acetate, and analyzed by ultra-performance liquid chromatography-mass-mass spectrometry (UPLC-MS/MS), and the functional faction was identified as an amicoumacin A compound. The organic extracts of CFS containing amicoumacin A had bactericidal effects on V. parahaemolyticus, and the treated V. parahaemolyticus cells showed disruption of the cell membrane and formation of cell cavities. These findings indicate that B. subtilis strain O-741 can inhibit the V. parahaemolyticus in vitro and in vivo, and has potential for use as a biocontrol agent for preventing V. parahaemolyticus infection.

Strain-Specific Benefits of Bacillus Probiotics in Hybrid Grouper: Growth Enhancement, Metabolic Health, Immune Modulation, and Vibrio harveyi Resistance

In the realm of modern aquaculture, the utilization of probiotics has gained prominence, primarily due to their ability to enhance growth, boost immunity, and prevent diseases in aquatic species. This study primarily investigates the efficacy of Bacillus subtilis strains, both host-derived and from other sources, in influencing fish growth, immunity, lipid metabolism, and disease resistance. Employing a 42-day feeding trial, we divided hybrid grouper into four distinct groups: a control group on a basal diet and three experimental groups supplemented with 1 × 108 CFU/g of different Bacillus subtilis strains-BS, 6-3-1, and HAINUP40. Remarkably, the study demonstrated that the 6-3-1 and HAINUP40 groups exhibited significant enhancements across key growth parameters: final body weight (FBW), weight gain rate (WGR), feed intake (FI), feed efficiency ratio (FER), and feed conversion ratio (FCR). The investigation into lipid metabolism revealed that the 6-3-1 strain upregulated seven metabolism-related genes, HAINUP40 affected four metabolism-related genes, and the BS strain influenced two metabolism-related genes, indicating diverse metabolic impacts by different strains. Further, a notable reduction in liver enzymes AST and ALT was observed across all supplemented groups, implying improved liver health. Noteworthy was the BS strain's superior antioxidative capabilities, positively affecting all four measured parameters (CAT, GSH-Px, MDA). In the sphere of immune-related gene expression, the BS strain significantly decreased the expression of both inflammation and apoptosis-related genes, whereas the HAINUP40 strain demonstrated an upregulation in these genes. The challenge test results were particularly telling, showcasing improved survival rates against Vibrio harveyi infection in the BS and 6-3-1 groups, unlike the HAINUP40 group. These outcomes highlight the strain-specific nature of probiotics and their varying mechanisms of action within the host. In conclusion, this study reveals that probiotic strains, varying by source, demonstrate unique, strain-specific effects in promoting growth and modulating immunity in hybrid grouper. This research highlights the promise of tailored probiotic applications in improving aquaculture practices. Such advancements contribute to more sustainable and efficient fish farming methods.

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.

Evaluating Bacillus flexus as bioremediators for ammonia removal in shrimp culture water and wastewater and characterizing microbial communities in shrimp pond sludge

The accumulation of nitrogen compounds in shrimp farming water and effluent presents a major challenge. Ammonia is a form of nitrogen that limits shrimp growth due to its potential toxicity and effects on shrimp health and water quality. This study is aimed at identifying promising bioremediators from shrimp pond sludge to mitigate ammonia levels in both culture water and wastewater and at determining major bacterial communities in sludge using metagenomic analysis. A sludge sample was collected from a shrimp pond in Selangor, Malaysia, to isolate potential ammonia-removing bacteria. Out of 64 isolated strains, Bacillus flexus SS2 showed the highest growth in synthetic basal media (SBM) containing ammonium sulfate at a concentration of 70 mg/L as the sole nitrogen source. The strain was then incubated in SBM with varying pH levels and showed optimal growth at pH 6.5-7. After 24 h of incubation, B. flexus SS2 reduced the ammonia concentration from an initial concentration of 5 to 0.01 mg/L, indicating a 99.61% reduction rate, which was highest in SBM at pH 7. Moreover, the strain showed ammonia removal ability at concentrations ranging from 5 to 70 mg/L. Metagenomic analysis revealed that Proteobacteria was the most abundant phylum in the sludge, followed by Cyanobacteria, Actinobacteria, Chloraflexi, Firmicutes, and Campilobacterota. Bacillus flexus SS2 belongs to the Bacillota phylum and has the potential to serve as a bioremediator for removing ammonia from shrimp culture water and wastewater.

Multi-omics analysis revealed the differences in lipid metabolism of the gut between adult and juvenile yellowfin tuna (Thunnus albacares)

Introduction

Tuna has a cost-effective energy supply to support the regional endothermic and high-speed swimming performance. The gut symbiotic microbiotas and their metabolites play essential roles in tuna's diet digestion, absorption, and energy acquirement, which are often highly related to the ontogenetic development of tuna.

Methods

We compared gut microbial compositions and metabolites, as well as mRNA expression of the intestine between juvenile and adult yellowfin tuna using 16S rRNA sequencing, metabolomic and transcriptomic, respectively.

Results and discussion

The results revealed that adults had a significantly higher microbial diversity and abundance of Acinetobacter than juveniles. Regarding the gut microbiota-derived metabolites, fatty acids, especially glycerophospholipid and sphingolipid, were significantly enriched in adults than in juveniles. Moreover, the short-chain fatty acid (butyrate and isobutyrate) contents were significantly higher in adults than in juveniles. To find the relationship between gut microbiotas and host physiology, intestinal transcriptome analysis demonstrated that the enriched pathways of differential expression genes (DEGs) in adult tuna were the lipid metabolism pathway, including "fat digestion and absorption," "cholesterol metabolism," "steroid hormone biosynthesis," "glycerolipid metabolism," and "glycerophospholipid metabolism." However, protein digestion and absorption and pancreatic secretion pathways were significantly enriched in the juveniles. The conjoint analysis indicated that the enriched pathways of both differential metabolites (DMs) and DEGs were remarkably related to the regulation of glycerophospholipids metabolism in adult tunas. This study highlights the role of gut microbiotas in fish nutrition metabolism. These findings provide new insights into the view of ontogenetic shifts of gut microbiotas and their metabolites on host health and gut function in endothermic and high-speed swimming marine fish species.

Biodegradation mechanism of chlorpyrifos by Bacillus sp. H27: Degradation enzymes, products, pathways and whole genome sequencing analysis

Chlorpyrifos (CP) is a pesticide widely used in agricultural production. However, excessive use of CP is risky for human health and the ecological environment. Microbial remediation has become a research hotspot of environmental pollution control. In this study, the effective CP-degrading strain H27 (Bacillus cereus) was screened from farmland soil, and the degradation ratio was more than 80%. Then, the degradation mechanism was discussed in terms of enzymes, pathways, products and genes, and the mechanism was improved in terms of cell motility, secretory transport system and biofilm formation. The key CP-degrading enzymes were mainly intracellular enzymes (IE), and the degradation ratio reached 49.6% within 30 min. The optimal pH for IE was 7.0, and the optimal temperature was 25 °C. Using DFT and HPLC‒MS analysis, it was found that degradation mainly involved oxidation, hydrolysis and other reactions, and 3 degradation pathways and 14 products were identified, among which TCP (3,5,6-trichloro-2-pyridinol) was the main primary degradation product in addition to small molecules such as CO2 and H2O. Finally, the whole genome of strain H27 was sequenced, and the related degrading genes and enzymes were investigated to improve the metabolic pathways. Strain H27 had perfect genes related to flagellar assembly and chemotaxis and tended to tolerate CP. Moreover, it can secrete esterase, phosphatase and other substances, which can form biofilms and degrade CP in the environment. In addition, CP enters the cell under the action of permeases or transporters, and it is metabolized by IE. The degradation mechanism of CP by strain H27 is speculated in this study, which provided a theoretical basis for enriching CP-degrading bacteria resources, improving degradation metabolic pathways and mechanisms, and applying strain H27 to environmental pollution remediation.

Effects of dietary supplementation of Bacillus subtilis DSM 32315 on growth, immune response and acute ammonia stress tolerance of Nile tilapia (Oreochromis niloticus) fed with high or low protein diets

Aquatic animals have benefited from Bacillus subtilis-based probiotics over the past few decades. This study evaluated the effects of B. subtilis DSM 32315 probiotics as a feed additive on growth, immune response and resistance to acute ammonia challenge in Nile tilapia. Specifically, four supplemental levels (0%, 0.1%, 0.2%, and 0.3%) of B. subtilis probiotics were tested under two dietary protein levels (32% and 28%). Five replicate tanks were randomly allotted to each dietary treatment, with each tank containing 30 Nile tilapia. After 8 weeks of feeding, Nile tilapia in each tank were exposed to 43.61 mg/L of total ammonia nitrogen for 48 h. The results revealed that reducing protein levels from 32% to 28% did not affect growth performance or antioxidant capacity. However, the low protein diet tended to induce an inflammatory effect shown by increased expressions of TGF-β and IFN-γ genes (P < 0.05) in the liver. The impact was alleviated by the probiotic supplementation. Compared with the non-supplemented group, 0.1% probiotic supplementation remarkably increased plasma lysozyme activity, total antioxidant capacity and complement C3 and interleukin-10 mRNA levels (P < 0.05) in the 28% protein diet, while higher supplementation of probiotics (0.3%) was shown to be beneficial for the high protein diet (32%). In both the dietary protein levels, 0.1% supplementation of probiotics promoted the antioxidant capacity of Nile tilapia before exposure to ammonia stress but higher probiotic supplementation (0.3%) proved to be necessary under ammonia stress as evidenced by higher fish survival rate. Results exhibited that supplementation with B. subtilis probiotics had a better effect on the intestinal morphology (villi height and width) regardless of protein levels. In conclusion, dietary supplementation of B. subtilis DSM 32315 probiotics at 0.1% in the low protein diet and up to 0.3% in the high protein diet showed beneficial effects on the growth, immunity, and antioxidant capacity of Nile tilapia. Under ammonia stress conditions, the higher supplementation of B. subtilis DSM 32315 probiotics at 0.3% improves stress tolerance of Nile tilapia despite the two dietary protein levels (32%; 28%).

In vitro determination of probiotic efficacy of Bacillus subtilis TLDK301120C24 isolated from tilapia against warm water fish pathogens and in vivo validation using gnotobiotic zebrafish model

Eco-friendly alternatives such as probiotics are needed to prevent economically relevant infectious diseases for a successful disease-free harvest in aquaculture. The use of antibiotics has been the favored practice, but its empirical and indiscriminate use has led to antibiotic resistance in the aquatic environment and residues in the food fish. With this rationale, a probiotic was isolated from tilapia, a commercially important cultured fish worldwide. The characteristics of the probiotic were checked against common bacterial pathogens affecting aquaculture. In vitro tests demonstrated the inhibitory effects of the isolated probiotic on the growth of Aeromonas hydrophila, Edwardsiella tarda, Vibrio anguillarum, and V. alginolyticus. The candidate probiotic, referred to as TLDK301120C24, was identified as Bacillus subtilis by a battery of biochemical tests and genotypic confirmation by 16S rDNA sequencing. The in vitro results revealed the ability of the probiotic to withstand the gut conditions that included pH range of 3-9, salt concentration of 0.5-6%, and bile salt concentration of up to 6%. The isolate could hydrolyze starch (12-14 mm clearance zone), protein (20-22 mm clearance zone), and cellulose (22-24 mm clearance zone). Further, the inhibitory ability of the probiotic against aquatic pathogens was determined in vivo using gnotobiotic zebrafish by employing a novel approach that involved tagging the probiotic with a red fluorescent protein and the pathogens with a green fluorescent protein, respectively. The colonizing ability of probiotics and its inhibitory effects against the pathogens were evaluated by fluorescence microscopy, PCR, and estimation of viable counts in LBA + Amp plates. Finally, the competitive inhibition and exclusion of fish pathogens A. hydrophila and E. tarda by B. subtilis was confirmed semi-quantitatively, through challenge experiments. This study shows the potential of B. subtilis as a probiotic and its excellent ability to inhibit major fish pathogens in vivo and in vitro. It also shows promise as a potent substitute for antibiotics.

Live Yeast (Saccharomyces cerevisiae var. boulardii) Supplementation in a European Sea Bass (Dicentrarchus labrax) Diet: Effects on the Growth and Immune Response Parameters

The present study has been aimed at evaluating the effects of the dietary inclusion of the live yeasts, Saccharomyces cerevisiae var. boulardii (LSB) administered at increasing concentrations (0, 100, and 300 mg kg-1 of feed, here referred to as LSB 0, 100, 300) for 90 days, on the health conditions of European sea bass. The main zootechnical parameters, histological and morphological analyses, innate immunity response parameters (intestinal cytokine expression, lysozyme content, spontaneous hemolytic and hemagglutinating activities, antibacterial activities, and peroxidase activity) were measured as fish welfare parameters. LSB did not impair either growth parameters or the morphometric indexes. LSB down-regulated interleukin-1β transcription in the distal gut of fish treated with 5.4 × 105 CFU g-1 (LSB100) for 21 days. The interleukin-6 mRNA level decreased significantly in the proximal gut for both doses of yeast, after 21 days of feeding; the gene expression of interleukin-6 was significantly lower in the sea bass fed 10.81 × 105 CFU g-1 (LSB300) probiotic. The levels of TNF-α mRNA were not influenced by probiotic supplementation. Increases, although not significant, in the hematological and immunological parameters were also recorded. The data collected in the present study suggests that an LSB-supplemented diet acts on the gut immune system of sea bass by modulating the expression of the key inflammatory genes.

Probiotics enhance resistance to Streptococcus iniae in Nile tilapia (Oreochromis niloticus) reared in biofloc systems

Biofloc technology is a rearing technique that maintains desired water quality by manipulating carbon and nitrogen and their inherent mixture of organic matter and microbes. Beneficial microorganisms in biofloc systems produce bioactive metabolites that may deter the growth of pathogenic microbes. As little is known about the interaction of biofloc systems and the addition of probiotics, this study focused on this integration to manipulate the microbial community and its interactions within biofloc systems. The present study evaluated two probiotics (B. velezensis AP193 and BiOWiSH FeedBuilder Syn 3) for use in Nile tilapia (Oreochromis niloticus) culture in a biofloc system. Nine independent 3785 L circular tanks were stocked with 120 juveniles (71.4 ± 4.4 g). Tilapia were fed for 16 weeks and randomly assigned three diets: a commercial control diet or a commercial diet top-coated with either AP193 or BiOWiSH FeedBuilder Syn3. At 14 weeks, the fish were challenged with a low dose of Streptococcus iniae (ARS-98-60, 7.2 × 107  CFU mL-1 , via intraperitoneal injection) in a common garden experimental design. At 16 weeks, the fish were challenged with a high dose of S. iniae (6.6 × 108  CFU mL-1 ) in the same manner. At the end of each challenge trial, cumulative per cent mortality, lysozyme activity and expression of 4 genes (il-1β, il6, il8 and tnfα) from the spleen were measured. In both challenges, the mortalities of the probiotic-fed groups were significantly lower (p < .05) than in the control diet. Although there were some strong trends, probiotic applications did not result in significant immune gene expression changes related to diet during the pre-trial period and following exposure to S. iniae. Nonetheless, overall il6 expression was lower in fish challenged with a high dose of ARS-98-60, while tnfα expression was lower in fish subjected to a lower pathogen dose. Study findings demonstrate the applicability of probiotics as a dietary supplement for tilapia reared in biofloc systems.

Bacterial diseases in marine fish species: current trends and future prospects in disease management

The fisheries sub-sector of aquaculture-i.e., the pisciculture industry, contributes significantly to a country's economy, employing a sizable proportion of the population. It also makes important contributions to household food security because the current demand for animal protein cannot be fulfilled by harvesting wild fish from riverines, lakes, dams, and oceans. For good pond management techniques and sustaining fish health, the fisherfolk, and the industry require well-established regulatory structures, efficient disease management strategies, and other extended services. In rearing marine fish, infections resulting from disease outbreaks are a weighty concern because they can cause considerable economic loss due to morbidity and mortality. Consequently, to find effective solutions for the prevention and control of the major diseases limiting fish production in aquaculture, multidisciplinary studies on the traits of potential fish pathogens, the biology of the fish as hosts, and an adequate understanding of the global environmental factors are fundamental. This review highlights the various bacterial diseases and their causative pathogens prevalent in the pisciculture industry and the current solutions while emphasising marine fish species. Given that preexisting methods are known to have several disadvantages, other sustainable alternatives like antimicrobial peptides, synthetic peptides, probiotics, and medicinal treatments have emerged to be an enormous potential solution to these challenges.

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

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

The Synergic Effect of Gut-Derived Probiotic Bacillus cereus SL1 And Ocimum sanctum on Growth, Intestinal Histopathology, Innate Immunity, and Expression of Enzymatic Antioxidant Genes in Fish, Cirrhinus mrigala (Hamilton, 1822)

An effective alternative approach to combat aquaculture challenges is the strategic application of bioresources, which not only mitigate disease ailment but also optimize fish growth. Hence, current research was undertaken to highlight the synergic role of bioresources such as plant immunostimulant Ocimum sanctum along with potent gut-derived probiotic Bacillus cereus strain SL1 (Gen Bank Accession Number: FJ627945.1) on mrigal (Cirrhinus mrigala) growth, antioxidant status, gut histopathology, and immune response. For 90 days, fingerlings (average weight 6.8 ± 0.5 g) were fed on diets having varying concentrations of O. sanctum and B. cereus. After the completion of the feeding trial, various growth, immunity, and histological and antioxidant metrics were evaluated according to standard procedures. In comparison to the control and other treatment groups, T3 group showed a significant (P < 0.05) increase in growth parameters, antioxidant enzymatic activity, and hematological and immunological parameters. In addition to it, supplementation of both B. cereus and O. sanctum also upregulated the antioxidant-related gene expressions, such as hepatic catalase gene by 1.89-3.00 folds, hepatic SOD-1 by 4.46-7.52 folds, and GPx-1of the liver by 1.56-1.95 folds. For 10 days, fingerlings were challenged with the pathogenic bacterium Aeromonas hydrophila (MTCC-1739), and maximum survival rate (77.77%) was reported in fingerlings of T3 treatment. Further histopathological studies of gut tissues affirm that O. sanctum and B. cereus play a synergic role in the protection of digestive organs from the pathogenic bacterium A. hydrophila. These results suggest that O. sanctum and B. cereus synergically improved the growth performance, immunity, antioxidant status, and gut histology of C. mrigala leading to its sustainable culture.

Functionality of probiotics on the resistance capacity of shrimp against white spot syndrome virus (WSSV)

Shrimp aquaculture is currently regarded as a significant commercial and food production sector due to its growing importance as a source of human-consumable protein, As shrimp farming has become more intensive, disease outbreaks have become more common, necessitating the overuse of antimicrobial drugs, which has had a number of unintended consequences. The white spot syndrome virus (WSSV) is now recognized as one of the world's most pervasive and potentially fatal diseases affecting shrimp. However, there is currently no cure to prevent the disease's uncontrolled incidence and spread. Probiotics are currently favoured over these antimicrobial substances because of their ability to stimulate disease resilience in shrimp farms by strengthening the immune systems naturally. Probiotics for bacterial infections such as vibriosis are well documented, whereas research is still required to identify the legitimate strains for viral diseases. The utilization of these probiotics as a therapy for and preventative measure against WSSV in shrimp farming is a cutting-edge method that has proven to be effective. Some probiotic strains, such as Bacillus spp, Lactobacillus, and Pediococcus pentosaceus, have been displayed to enhance the innate immunity of shrimp against WSSV, reduce viral load, increase digestibility and growth, and support the gut microbiome of the host in multiple investigations. The present review explores recent developments regarding the function of probiotics in shrimp, with a focus on their anti-WSSV activity.

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.

Autochthonous Bacilli and Fructooligosaccharide as Functional Feed Additives Improve Growth, Feed Utilisation, Haemato-Immunological Parameters and Disease Resistance in Rohu, Labeo rohita (Hamilton)

The effects of Bacillus spp. (7 Log CFU g-1 feed) and fructooligosaccharide (FOS, 1%) as functional feed additives, either alone or in combination, were evaluated in a study on rohu, Labeo rohita fingerlings. The fish were fed different diets for 90 days, including a control diet and diets supplemented with FOS, B. licheniformis, B. methylotrophicus or synbiotic formulations of these. The results showed that the combination of B. licheniformis and FOS significantly improved weight gain, feed utilisation and protease activity compared to the other groups. Overall, the groups supplemented with probiotics and synbiotics (B. licheniformis + FOS or B. methylotrophicus + FOS) showed improvements in haematology, serum biochemistry and immune parameters compared to the control group. After 90 days of experimental feeding, the fish were challenged with pathogenic Aeromonas hydrophila, and data on haematology, immunity and stress parameters were collected. The results indicated that the application of Bacillus spp. and FOS boosted immunity and resistance to physiological stress in the fish. The highest post-challenge survival rate was observed in fish fed a diet with B. licheniformis and FOS, indicating the potential of this particular combination of functional feed additives to enhance growth, immunity and disease resistance in L. rohita.

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.

Efficacy of dietary live or heat-killed Bacillus subtilis in goldfish (Carassius auratus) infected with Ichthyophthirius multifiliis

BACKGROUND

The beneficial effects of Bacillus subtilis on growth, immune response, and disease resistance against various diseases in different fish species have been proved. However, there are no data concerning this probiotic effect on skin mucosal immunity in fish infected with Ichthyophthirius multifiliis (Ich). Ich has a high mortality rate in both edible and ornamental fish and consequently is concerned with heavy economic losses.

OBJECTIVES

Thus, we assessed the efficacy of live and heat-killed B. subtilis on skin immunity and histopathology in goldfish (Carassius auratus) infected with Ich.

METHODS

Goldfish (144 fish, 2.38 g average weight) were stocked in nine glass tanks each in three replicates. Fish were fed 10⁹ CFU g^-1 live or heat-killed B. subtilis for 80 days.

RESULTS

Probiotic administration in both viable and non-viable forms could enhance the growth performance in goldfish. Probiotic therapy also reduced the density of the parasite and histopathological level on skin and gill tissues of the treated fish. Real-time polymerase chain reaction analysis showed a higher expression of lysozyme and tumour necrosis factor-α in the treated groups compared to the control group.

CONCLUSIONS

These data demonstrated the beneficial effect of B. subtilis as probiotic and paraprobiotic on growth performance and disease resistance to Ich infestation in goldfish.

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

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

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

Recirculating packed-bed biofilm photobioreactor combined with membrane ultrafiltration as advanced wastewater treatment

Packed-bed biofilm photobioreactor combined with ultrafiltration membrane was investigated for intensifying the process for secondary wastewater effluent treatment. Cylindrical glass carriers were used as supporting material for the microalgal-bacterial biofilm, which developed from indigenous microbial consortium. Glass carriers allowed adequate growth of the biofilm with limited suspended biomass. Stable operation was achieved after a start-up period of 1000 h, where supernatant biopolymer clusters were minimized and complete nitrification was observed. After that time, biomass productivity was 54 ± 18 mg·L^-1·day^-1. Green microalgae Tetradesmus obliquus and several strains of heterotrophic nitrification-aerobic denitrification bacteria and fungi were identified. Combined process exhibited COD, nitrogen and phosphorus removal rates of 56 ± 5%, 12 ± 2% and 20 ± 6%, respectively. Membrane fouling was mainly caused by biofilm formation, which was not effectively mitigated by air-scouring aided backwashing.

Nutrient enrichment drives the sediment microbial communities in Chinese mitten crab Eriocheir sinensis culture

Microbial communities play a critical role in aquaculture ecosystems. To identify the influence of sediment nutrient levels on microbial communities, sediment and water samples were collected from Chinese mitten crab Eriocheir sinensis culture ponds with different nutrient enrichment levels. Relevant physicochemical properties were measured, and 16 S rRNA gene sequencing was applied to identify relevant bacterial communities in the sediments. The results showed that the diversity and composition of microbial communities in sediments with different levels of nutrient enrichment varied considerably. Proteobacteria was the most abundant phylum in all samples, followed by Bacteroidetes, and Desulfobacterota with relative abundances of 23.5-40.9%, 9.8-21.5%, and 9.6-18.1%, respectively. Notably, total nitrogen (TN), organic matter (OM), and pH were important factors driving sediment bacterial community aggregation, the TN concentration explaining 61.5% of the microbial community variation. This study highlights that long-term culture activities alter the degree of sediment nutrient enrichment, which in turn affects microbial community composition and may ultimately have an impact on culture efficiency.

Increased abundances of potential pathogenic bacteria and expressions of inflammatory cytokines in the intestine of oyster Crassostrea gigas after high temperature stress

High temperature stress is a significant threat to the health of oysters, but the effects on their intestinal performances are not well understood. In this study, the effects of high temperature stress on the intestinal histology, immune response and associated microbiota were investigated in Crassostrea gigas after rearing at 20, 25 and 28 °C for 21 days. With the increase of temperature, shortened and shed microvilli as well as increased goblet cells were observed in the intestines of oysters. The transcripts of cytokines CgIL17-5, CgTNF-2 and CgTGF-β and apoptosis-related gene CgCaspase-3 in intestine increased with the increasing temperature. Further, the diversity and composition of the oyster intestinal microbiota changed after high temperature stress. The 16S rRNA gene copy number per ng of DNA in the T25 (5.16 × 10⁵) and T28 (1.63 × 10⁵) groups were higher than that in the control group (8.62 × 10⁴). The Chao 1 index in the T25 (238.00) and T28 (240.17) groups was lower than that in the control group (279.00). The Shannon index decreased progressively with the increasing temperature, with the value in the T28 group (4.44) significantly lower than that in the control group (5.40) (p < 0.05). The abundances of potential pathogenic bacteria such as Acinetobacter, Pseudomonas, Vibrio and Endozoicomonas increased while that of probiotic bacteria Bacillus decreased after high temperature exposure. Functional prediction indicated that the pathways associated with bacterial proliferation were enriched at 25 °C, while those involved in protein synthesis were blocked at 28 °C. Collectively, these results suggested that high temperature stress led to an increased abundances of potential pathogenic bacteria and expressions of inflammatory cytokines in the intestine, which may consequently affect the functional integrity of the intestinal barrier in oysters.

Isolation and characterization of autochthonous probiotics from skin mucus and their in vivo validation with dietary probiotic bacteria on growth performance and immunity of Labeo calbasu (Hamilton, 1822)

The present study was performed to isolate and identify antimicrobial bacteria from the skin mucus of Labeo calbasu and assess their effects as water additives alone and in synergism, with dietary probiotic bacteria Aneurinibacillus aneurinilyticus LC1 isolated from intestinal tracts of L. calbasu on physiology and survival of same fish. Eight treatments (T1-T8) were conducted in triplicate, containing 10 fishes (2.02 ± 0.01 g) in each treatment: T1, control group (diet without probiotics); T2-T4, a diet with water additive probiotics; Bacillus cereus LC1, B. albus LC7, and B. cereus LC10, respectively, at 1000 CFU ml^-1; T5, a diet with dietary probiotic A. aneurinilyticus at 3000 CFU g^-1, T6-T8, a diet with water additives Bacillus cereus LC1, B. albus LC7, and B. cereus LC10 at 1000 CFU ml^-1 along with dietary probiotic A. aneurinilyticus at 3000 CFU g^-1. Results revealed improved growth, nutritive physiology, immune response, water quality, and survival in fish of group T8 (fingerlings fed on a probiotic diet at 3000 CFU g^-1 and reared in holding water treated with skin mucus bacteria B. cereus LC10 at 1000 CFU g^-1) as compared to other treatments, suggesting autochthonous intestinal and cutaneous mucosal bacteria as robust candidates for their collective application in aquaculture.

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

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

Bioremediation of Heavy Metals by the Genus Bacillus

Environmental contamination with heavy metals is one of the major problems caused by human activity. Bioremediation is an effective and eco-friendly approach that can reduce heavy metal contamination in the environment. Bioremediation agents include bacteria of the genus Bacillus, among others. The best-described species in terms of the bioremediation potential of Bacillus spp. Are B. subtilis, B. cereus, or B. thuringiensis. This bacterial genus has several bioremediation strategies, including biosorption, extracellular polymeric substance (EPS)-mediated biosorption, bioaccumulation, or bioprecipitation. Due to the above-mentioned strategies, Bacillus spp. strains can reduce the amounts of metals such as lead, cadmium, mercury, chromium, arsenic or nickel in the environment. Moreover, strains of the genus Bacillus can also assist phytoremediation by stimulating plant growth and bioaccumulation of heavy metals in the soil. Therefore, Bacillus spp. is one of the best sustainable solutions for reducing heavy metals from various environments, especially soil.

Effect of dietary Bacillus subtilis supplement on Cd toxicokinetics and Cd-induced immune and antioxidant impairment of Procambarus clarkii

Cadmium (Cd), a non-biodegradable contaminant in freshwater ecosystems, can pose a serious threat to aquatic animals at high levels. In this study, the Cd toxicokinetics and the immune and antioxidant defense were explored in Procambarus clarkii exposed to different levels of Cd (0, 0.1, 1.0 mg Cd/L) or treated with 1.0 mg Cd/L and dietary Bacillus subtilis supplementation (1 × 10⁷ cfu/g). Results from the 21-day uptake and depuration experiment revealed that Cd exposure elicited a dose- and time-dependent uptake in all crayfish tissues, and the rank order of Cd concentration was gill > hepatopancreas > exoskeleton > muscle. The one-compartment model demonstrated that gills had the highest uptake rate (k_u) value after Cd aqueous exposure and the k_u and elimination rate (k_d) values in gill, hepatopancreas, and exoskeleton of the group with 1.0 mg Cd/L were higher than those of the group at alow Cd concentration (0.1 mg Cd/L). However, B. subtilis could decrease Cd k_u and increase Cd k_d in hepatopancreas, resulting in the reduction of bioconcentration factors (BCF), steady-state concentrations (C_ss), and biological half-life (T_b1/2). A positive correlation was found between aqueous Cd concentration and the severity of hepatopancreas histopathological injury, while B. subtilis could ameliorate the pathological damage in the high Cd group. Similarly, aqueous exposure to Cd elevated malonaldehyde (MDA) content and suppressed the activities of lysozyme (LZM), acid phosphatase (ACP) in hepatopancreas and alkaline phosphatase (AKP) in hemolymph. The activities of superoxide dismutase (SOD) and catalase (CAT) in hepatopancreas were also inhibited. Nevertheless, they were all recovered with the dietary addition of B. subtilis. In conclusion, our results indicated that exposure to Cd significantly increased Cd accumulation and toxic damages in crayfish hepatopancreas, while dietary administration of B. subtilis to crayfish significantly decreased Cd accumulation and improved the immune and antioxidant defense, leading to the prevention in toxic effects of Cd.

Insight into the Cold Adaptation Mechanism of an Aerobic Denitrifying Bacterium: Bacillus simplex H-b

Psychrophilic bacteria with aerobic denitrification ability have promising potential for application in nitrogen-contaminated wastewater treatment, especially under cold conditions. A better understanding of the cold adaptation mechanism during aerobic denitrification would be beneficial for the practical application of this type of functional bacterium. In this study, Bacillus simplex H-b with good denitrification performance at 5°C was used to investigate the corresponding cold tolerance mechanism. Transcriptomics and nitrogen removal characterization experiments were conducted at different temperatures (5°C, 20°C, and 30°C). At low temperatures, more nitrogen was utilized for assimilation, accompanied by the accumulation of ATP and extracellular polymeric substances (EPS), rather than transforming inorganic nitrogen in the dissimilation pathway. In addition, the proportion of unsaturated fatty acids was higher in strains cultured at low temperatures. At the molecular level, the adjustment of membrane transport, synthesis of cofactors and vitamins, and transcriptional regulators might contribute to the survival of the strain under cold conditions. Moreover, nucleotide precursor synthesis, translation, and oxidative and temperature stress response mechanisms also enhanced the resistance of strain H-b to low temperatures. The results suggest that combining multiple regulatory mechanisms and synergistic adaptation to cold stress enabled the growth and relatively high nitrogen removal rate (27.22%) of strain H-b at 5°C. By clarifying the mechanism of regulation and cold resistance of strain H-b, a theoretical foundation for enhancing the application potential of this functional bacterium for nitrogen-contaminated wastewater treatment was provided. IMPORTANCE The newly isolated aerobic denitrifying bacterium Bacillus simplex H-b removed various forms of inorganic nitrogen (nitrate, nitrite, and ammonium) from wastewater, even when the temperature was as low as 5°C. Although this environmentally functional bacterium has been suggested as a promising candidate for nitrogen-contaminated water treatment at low temperatures, understanding its cold adaptation mechanism during aerobic denitrification is limited. In this study, the cold tolerance mechanism of this strain was comprehensively explained. Furthermore, a theoretical basis for the practical application of this type of functional bacterium for nitrogen removal in cold regions is provided. The study expands our understanding of the survival strategy of psychrophilic bacteria and hence supports their further utilization in wastewater treatment applications.