Effect of Bacillus velezensis on Aeromonas veronii-Induced Intestinal Mucosal Barrier Function Damage and Inflammation in Crucian Carp (Carassius auratus)

Effects of Aeromonas infection on the immune system, physical barriers and microflora structure in the intestine of juvenile grass carp (Ctenopharyngodon idella)

Grass carp (Ctenopharyngodon idella) is an intensively cultured and economically important herbivorous fish species in China, but its culture is often impacted by Aeromonas pathogens such as Aeromonas hydrophila and Aeromonas veronii. In this study, healthy grass carp were separately infected with A. hydrophila or A. veronii for 12, 24, 48 or 72 h. The results showed that the mRNA expression levels of intestinal inflammatory factors (tnf-α, il-1β and il-8), complement factors (c3 and c4), antimicrobial peptides (hepcidin, nk-lysin and β-defensin-1), immunoglobulins (igm and igt), and immune pathway-related signaling molecules (tlr1, tlr2, tlr4, myd88, irak4, irak1, traf6, nf-κb p65 and ap-1) were differentially upregulated in response to A. hydrophila and A. veronii challenge. Additionally, the expression levels of the intestinal pro-apoptotic genes tnfr1, tnfr2, tradd, caspase-8, caspase-3 and bax were significantly increased, whereas the expression of the inhibitory factor bcl-2 was significantly downregulated, indicating that Aeromonas infection significantly induced apoptosis in the intestine of grass carp. Moreover, the expression of intestinal tight junction proteins (occludin, zo-1, claudin b and claudin c) was significantly decreased after infection with Aeromonas. Histopathological analysis indicated the Aeromonas challenge caused severe damage to the intestinal villi with adhesions and detachment of intestinal villi accompanied by severe inflammatory cell infiltration at 12 h and 72 h. The 16S rRNA sequencing results showed that Aeromonas infection significantly altered the structure of the intestinal microflora of the grass carp at the phylum (Proteobacteria, Fusobacteria, Bacteroidetes and Firmicutes) and genus (Proteus, Cetobacterium, Bacteroides, and Aeromonas) levels. Take together, the findings of this study revealed that Aeromonas infection induces an intestinal immune response, triggers cell apoptosis, destroys physical barriers and alters microflora structure in the intestine of juvenile grass carp; the results will help to reveal the pathogenesis of intestinal bacterial diseases in grass carp.

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

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

Acanthopanax senticosus cultures fermented by Lactobacillus rhamnosus enhanced immune response through improvement of antioxidant activity and inflammation in crucian carp (Carassius auratus)

Lactic acid bacteria (LAB) have been recognized as safe microorganism that improve micro-flora disturbances and enhance immune response. A well-know traditional herbal medicine, Acanthopanax senticosus (As) was extensively utilized in aquaculture to improve growth performance and disease resistance. Particularly, the septicemia, skin wound and gastroenteritis caused by Aeromonas hydrophila threaten the health of aquatic animals and human. However, the effects of probiotic fermented with A. senticosus product on the immune regulation and pathogen prevention in fish remain unclear. Here, the aim of the present study was to elucidate whether the A. senticosus fermentation by Lactobacillus rhamnosus improve immune barrier function. The crucian carp were fed with basal diet supplemented with L. rhamnosus fermented A. senticosus cultures at 2 %, 4 %, 6 % and 8 % bacterial inoculum for 8 weeks. After trials, the weight gain rate (WGR), specific growth rate (SGR) were significantly increased, especially in LGG-6 group. The results confirmed that the level of the CAT, GSH-PX, SOD, lysozyme, and MDA was enhanced in fish received with probiotic fermented product. Moreover, the L. rhamnosus fermented A. senticosus cultures could trigger innate and adaptive immunity, including the up-regulation of the C3, C4, and IgM concentration. The results of qRT-PCR revealed that stronger mRNA transcription of IL-1β, IL-10, IFN-γ, TNF-α, and MyD88 genes in the liver, spleen, kidney, intestine and gills tissues of fish treated with probiotic fermented with A. senticosus product. After infected with A. hydrophila, the survival rate of the LGG-2 (40 %), LGG-4 (50 %), LGG-6 (60 %), LGG-8 (50 %) groups was higher than the control group. Meanwhile, the pathological damage of the liver, spleen, head-kidney, and intestine tissues of probiotic fermentation-fed fish could be alleviated after pathogen infection. Therefore, the present work indicated that L. rhamnosus fermented A. senticosus could be regard as a potential intestine-target therapy strategy to protecting fish from pathogenic bacteria infection.

Postbiotic potential of Bacillus velezensis KMU01 cell-free supernatant for the alleviation of obesity in mice

Attention toward the preventive effects of postbiotics on metabolic diseases has increased because of greater stability and safety over probiotics. However, studies regarding the bioactive effects of postbiotics, especially from probiotic Bacillus strains, are relatively limited. The anti-obesity effects of the cell-free culture supernatant of Bacillus velezensis KMU01 (CFS-B.vele) were evaluated using high-fat-diet (HFD)-induced mice. HFD-induced mice (n = 8 per group) received equal volumes of (1) CFS-B.vele (114 mg/kg) in PBS, (2) Xenical in PBS, or (3) PBS alone by oral gavage daily for 13 weeks. The results demonstrated that CFS-B.vele changed the gut microbiota and showed anti-obesity effects in HFD-induced obese mice. The elevated Firmicutes/Bacteroidota ratio induced by HFD was decreased in the CFS-B.vele group compared to the other groups (p < 0.05). The CFS-B.vele intervention led to the enrichment of SCFA-producers, such as Roseburia and Eubacterium, in the cecum, suggesting their potential involvement in the amelioration of obesity. Due to these changes, the various obesity-related biomarkers (body weight, fat in tissue, white adipose tissue weight and size, serum LDL-cholesterol level, hepatic lipid accumulation, and adipogenesis/lipogenesis-related gene/protein expression) were improved. Our findings suggest that CFS-B.vele has potential as a novel anti-obesity agent through modulation of the gut microbiota.

Targeted Screening of Fiber Degrading Bacteria with Probiotic Function in Herbivore Feces

Cellulolytic bacteria with probiotic functions play a crucial role in promoting the intestinal health in herbivores. In this study, we aimed to correlate the 16S rRNA gene amplicon sequencing and fiber-degrading enzyme activity data from six different herbivore feces samples. By utilizing the separation and screening steps of probiotics, we targeted and screened high-efficiency fiber-degrading bacteria with probiotic functions. The animals included Maiwa Yak (MY), Holstein cow (CC), Tibetan sheep (TS), Southern Sichuan black goat (SG), Sichuan white rex rabbit (CR), and New Zealand white rabbit (ZR). The results showed that the enzymes associated with fiber degradation were higher in goat and sheep feces compared to cattle and rabbit's feces. Correlation analysis revealed that Bacillus and Fibrobacter were positively correlated with five types of fiber-degrading related enzymes. Notably, the relative abundance of Bacillus in the feces of Tibetan sheep was significantly higher than that of other five herbivores. A strain TS5 with good cellulose decomposition ability from the feces of Tibetan sheep by Congored staining, filter paper decomposition test, and enzyme activity determination was isolated. The strain was identified as Bacillus velezensis by biological characteristics, biochemical analysis, and 16S rRNA gene sequencing. To test the probiotic properties of Bacillus velezensis TS5, we evaluated its tolerance to acid and bile salt, production of digestive enzymes, antioxidants, antibacterial activity, and adhesion ability. The results showed that the strain had good tolerance to pH 2.0 and 0.3% bile salts, as well as good potential to produce cellulase, protease, amylase, and lipase. This strain also had good antioxidant capacity and the ability to antagonistic Staphylococcus aureus BJ216, Salmonella SC06, Enterotoxigenic Escherichia coli CVCC196, and Escherichia coli ATCC25922. More importantly, the strain had good self-aggregation and Caco-2 cell adhesion rate. In addition, we tested the safety of Bacillus velezensis TS5 by hemolysis test, antimicrobial susceptibility test, and acute toxicity test in mice. The results showed that the strain had no hemolytic phenotype, did not develop resistance to 19 commonly used antibiotics, had no cytotoxicity to Caco-2, and did not have acute toxic harm to mice. In summary, this study targeted isolated and screened a strain of Bacillus velezensis TS5 with high fiber-degrading ability and probiotic potency. This strain can be used as a potential probiotic for feeding microbial preparations for ruminants.

Isolation and pathogenicity evaluation of Escherichia coli O157:H7 from common carp, Cyprinus carpio

Escherichia coli O157:H7 is the primary serotype of enterohaemorrhagic E. coli (EHEC), which can cause diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome. It is considered as a major health concern due to it being a zoonotic disease that is transmitted through food. In this study, a pathogenic bacterium was isolated from infected carp, which identified as E. coli O157:H7 named X21 through genetic sequencing, phylogenetic analysis, physiological and biochemical tests. In the experiment, crucian carp was used as a model to study the pathogenicity of the isolate, the pathological histological observations and cytokines expression of fish tissues were determined after bacterial challenge. The results showed that severe pathological damage observed in the liver, spleen, headkidney of fish infected with isolate X21. Besides, we found that accumulation of IgT+ B cells in the lamina propria of intestine, and up-regulation of SUCH-r, IL-1β, IL-10, IL-11, MyD88, and TNF-α gene in various tissues. After challenged, the survivability of crucian carp infected with isolate X21 stands at a mere 14.27%. To our knowledge, this is the first report that E. coli O157:H7 infected the freshwater fish C. carpio, which indicates that this bacterium is a potential threat to public health and freshwater fish aquaculture.

Novel, non-colonizing, single-strain live biotherapeutic product ADS024 protects against Clostridioides difficile infection challenge in vivo

BACKGROUND

The Centers for Disease Control and Prevention estimate that Clostridioides difficile (C. difficile) causes half a million infections (CDI) annually and is a major cause of total infectious disease death in the United States, causing inflammation of the colon and potentially deadly diarrhea. We recently reported the isolation of ADS024, a Bacillus velezensis (B. velezensis) strain, which demonstrated direct in vitro bactericidal activity against C. difficile, with minimal collateral impact on other members of the gut microbiota. In this study, we hypothesized that in vitro activities of ADS024 will translate in vivo to protect against CDI challenge in mouse models.

AIM

To investigate the in vivo efficacy of B. velezensis ADS024 in protecting against CDI challenge in mouse models.

METHODS

To mimic disruption of the gut microbiota, the mice were exposed to vancomycin prior to dosing with ADS024. For the mouse single-dose study, the recovery of ADS024 was assessed via microbiological analysis of intestinal and fecal samples at 4 h, 8 h, and 24 h after a single oral dose of 5 × 108 colony-forming units (CFU)/mouse of freshly grown ADS024. The single-dose study in miniature swine included groups that had been pre-dosed with vancomycin and that had been exposed to a dose range of ADS024, and a group that was not pre-dosed with vancomycin and received a single dose of ADS024. The ADS024 colonies [assessed by quantitative polymerase chain reaction (qPCR) using ADS024-specific primers] were counted on agar plates. For the 28-d miniature swine study, qPCR was used to measure ADS024 levels from fecal samples after oral administration of ADS024 capsules containing 5 × 109 CFU for 28 consecutive days, followed by MiSeq compositional sequencing and bioinformatic analyses to measure the impact of ADS024 on microbiota. Two studies were performed to determine the efficacy of ADS024 in a mouse model of CDI: Study 1 to determine the effects of fresh ADS024 culture and ADS024 spore preparations on the clinical manifestations of CDI in mice, and Study 2 to compare the efficacy of single daily doses vs dosing 3 times per day with fresh ADS024. C. difficile challenge was performed 24 h after the start of ADS024 exposure. To model the human distal colon, an anerobic fecal fermentation system was used. MiSeq compositional sequencing and bioinformatic analyses were performed to measure microbiota diversity changes following ADS024 treatment. To assess the potential of ADS024 to be a source of antibiotic resistance, its susceptibility to 18 different antibiotics was tested.

RESULTS

In a mouse model of CDI challenge, single daily doses of ADS024 were as efficacious as multiple daily doses in protecting against subsequent challenge by C. difficile pathogen-induced disease. ADS024 showed no evidence of colonization based on the observation that the ADS024 colonies were not recovered 24 h after single doses in mice or 72 h after single doses in miniature swine. In a 28-d repeat-dose study in miniature swine, ADS024 was not detected in fecal samples using plating and qPCR methods. Phylogenetic analysis performed in the human distal colon model showed that ADS024 had a selective impact on the healthy human colonic microbiota, similarly to the in vivo studies performed in miniature swine. Safety assessments indicated that ADS024 was susceptible to all the antibiotics tested, while in silico testing revealed a low potential for off-target activity or virulence and antibiotic-resistance mechanisms.

CONCLUSION

Our findings, demonstrating in vivo efficacy of ADS024 in protecting against CDI challenge in mouse models, support the use of ADS024 in preventing recurrent CDI following standard antibiotic treatment.

Comparative genomic and transcriptome analysis of Bacillus velezensis CL-4 fermented corn germ meal

Bacillus, an excellent organic-degrading agent, can degrade lignocellulose. Notably, some B. velezensis strains encode lignocellulases. However, their ability to degrade lignocellulose in fermented feed is not much appreciated. This study performed a comparative genomic analysis of twenty-three B. velezensis strains to find common carbohydrate-active enzymes (CAZymes) encoding genes and evaluated their potential to degrade lignocellulose. The comparative genomic and CAZyme database-based analyses identified several potential CAZymes genes that degrade cellulose (GH1, GH4, GH5, GH13, GH16, GH32, PL1, and PL9), hemicellulose (GH11, GH26, GH43, GH51, and CE3) and lignin (AA4, AA6, AA7, and AA10). Furthermore, Illumina RNA-seq transcriptome analysis revealed the expression of more than 1794 genes in B. velezensis CL-4 fermented corn germ meal at 48 h (FCGM 48 h). Gene ontology analysis of expressed genes revealed their enrichment in hydrolase activity (breaking the glycosyl bonds during carbohydrate metabolism), indicating the upregulation of CAZymes. In total, 58 differentially upregulated CAZymes-encoding genes were identified in FCGM 48 h compared to FCGM 0 h. The upregulated CAZymes-encoding genes were related to cellulose (6-phospho-β-galactosidase and 6-phospho-α-glucosidase), starch (α-glucosidase and α-amylase), pectin (pectin lyase), and hemicellulose (arabinan endo-1,5-α-L-arabinosidase, xylan 1,4-beta-xylosidase, α-N-arabinofuranosidase, and acetyl xylan esterase). Importantly, arabinoxylan degradation mainly occurred in FCGM 48 h, followed by partial degradation of cellulose, pectin, and starch. This study can support the development of enzymatic cocktails for the solid-state fermented feed (SFF).

Dietary supplementation of probiotics fermented Chinese herbal medicine Sanguisorba officinalis cultures enhanced immune response and disease resistance of crucian carp (Carassius auratus) against Aeromonas hydrophila

Aeromonas hydrophila, a Gram-negative bacterium, is one of the major pathogens causing bacterial sepsis in aquatic animals due to drug resistance and pathogenicity, which could cause high mortality and serious economic losses to the aquaculture. Sanguisorba officinalis (called DiYu in Chinese, DY) is well known as herbal medicine, which could inhibit the growth of pathogenic bacteria, hemostasis and regulate the immune response. Moreover, the active ingredients in DY could remarkably reduce drug resistance. In this study, we investigated the effects of probiotic fermentation cultures on A. hydrophila through in vitro and in vivo experiments. Three lactic acid bacteria, including Lactobacillus rhamnosus (LGG), Lactobacillus casei (LC) and Lactobacillus plantarum (LP), were selected to ferment the Chinese herbal medicine DY. The assays of antagonism showed that all three fermented cultures could influence the ability of A. hydrophila growth, among which L. rhamnosus fermented DY cultures appeared to be the strongest inhibitory effect. In addition, the biofilm determination revealed that L. rhamnosus fermented DY cultures could significantly inhibit the biofilm formation of A. hydrophila compared to the other groups. Furthermore, protease, lecithinase and urease activities were found in the three fermentation cultures. Three probiotics fermented DY cultures were orally administration with crucian carp to evaluate the growth performance, immunological parameters and pathogen resistance. The results showed that the three fermentation cultures could promote the growth performance of crucian carp, and the immunoglobulins, antioxidant-related enzymes and immune-related genes were significantly enhanced. Besides, the results showed that crucian carp received L. rhamnosus (60.87%), L. casei (56.09%) and L. plantarum (41.46%) fermented DY cultures had higher survival rates compared with the control group after infection with A. hydrophila. Meanwhile, the pathological tissue results revealed that the probiotic fermented cultures could largely improve the tissues damage caused by the pathogenic bacteria. In conclusion, this study proved that the fermentation cultures of three probiotics could effectively inhibit the growth of A. hydrophila, regulate the level of immune response and improve the survival rate against A. hydrophila in crucian carp. The present data suggest that probiotic fermented Sanguisorba officinalis act as a potential gut-targeted therapy regimens to protecting fish from pathogenic bacteria infection.

Probiotics Bacillus cereus and B. subtilis reshape the intestinal microbiota of Pengze crucian carp (Carassius auratus var. Pengze) fed with high plant protein diets

The intestinal dysfunction induced by high plant protein diets is frequently observed in farmed fish, and probiotics of Bacillus genus were documented to benefit the intestinal health through the modulation of intestinal microbiota without clearness in its underlying mechanism yet. Fusobacteria, Proteobacteria, and Firmicutes were observed to be the dominate phyla, but their proportion differentiated in the intestinal bacterial community of Pengze crucian carp (Carassius auratus var. Pengze) fed different diets in this study. Dietary supplementation of B. cereus and B. subtilis could reshape the intestinal bacterial community altered by high plant protein diets through a notable reduction in opportunistic pathogen Aeromonas together with an increase in Romboutsia and/or Clostridium_sensu_stricto from Firmicutes. Due to the alteration in the composition of bacterial community, Pengze crucian carp exhibited characteristic ecological networks dominated by cooperative interactions. Nevertheless, the increase in Aeromonas intensified the competition within bacterial communities and reduced the number of specialists within ecological network, contributing to the microbial dysbiosis induced by high plant protein diets. Two probiotics diets promoted the cooperation within the intestinal bacterial community and increased the number of specialists preferred to module hubs, and then further improved the homeostasis of the intestinal microbiota. Microbial dysbiosis lead to microbial dysfunction, and microbial lipopolysaccharide biosynthesis was observed to be elevated in high plant protein diets due to the increase in Aeromonas, gram-negative microbe. Probiotics B. cereus and B. subtilis restored the microbial function by elevating their amino acid and carbohydrate metabolism together with the promotion in the synthesis of primary and secondary bile acids. These results suggested that dietary supplementation of probiotics B. cereus and B. subtilis could restore the homeostasis and functions of intestinal microbiota in Pengze crucian carp fed high plant protein diets.

Acute septicemia and immune response of spotted sea bass (Lateolabrax maculatus) to Aeromonas veronii infection

A previous study confirmed that spotted sea bass (Lateolabrax maculatus), an economically important cultured species in East Asia, is a new host of Aeromonas veronii, which can cause acute death in these fish, but there is little in-depth understanding of this disease. In the present study, the virulence of 10 isolates of A. veronii derived from spotted sea bass was determined. It was found that the 18BJ181 isolate was a virulent strain and led to the fastest death of spotted sea bass. Death was determined to be within in 2-12 h, and resulted in abdominal effusion and varying degrees of hemorrhage in internal organs. Bacterial colonization analysis showed that the bacterial load in the spleen was highest, and was up to 3.1 × 10⁵ cfu g^-1. In addition, the bacteria proliferated massively in the blood and reached 2.4 × 10⁷ cfu mL^-1 at 12 h after 18BJ181 strain infection, which was also a typical feature of acute septicemia. Histopathology of the spleen revealed edema in interstitial tissue, degeneration, and necrosis in lymphoid tissue, and hemorrhage in the capillary network. Transcriptome analysis of the spleen showed that the expression level of HSP70, CCL19, and IL-1β was extremely significantly up-regulated at 8 h after infection (P < 0.01), and the expression of these genes was normal at 24 h. These results revealed that A. veronii infection could rapidly activate the chemokine signal pathway and stimulate the acute inflammatory response in the host. The bacterial colonization, pathological features, and gene expression patterns in immune pathways will help us to better understand acute septicemia in spotted sea bass caused by A. veronii.

Comparative Study of Bacillus amyloliquefaciens X030 on the Intestinal Flora and Antibacterial Activity Against Aeromonas of Grass Carp

Beneficial microorganisms to control bacterial diseases has been widely used in aquaculture, Bacillus amyloliquefaciens (BaX030) as a probiotic feed additive was a commonly biological control method. Added sucrose promoted the growth of BaX030, and the yield of its antibacterial substance macrolactin A was enhanced by 1.46-fold. A total of 2055 proteins were screened through proteomics, with 143 upregulated and 307 downregulated. Differential protein expression analysis and qRT-PCR verification showed that the pentose phosphate pathway and the fatty acid synthesis pathway were upregulated, thereby providing sufficient energy and precursors for the synthesis of macrolactin A. The influence of some potential regulatory factors (SecG, LiaI, MecG and ComG) on macrolactin A was discovered. After grass carp were fed with BaX030, the abundance of probiotics (Fusobacterium, Proteobacteria, Gemmobacter) were higher than the control group, and the abundance of potential pathogenic bacteria (Planctomycetes, Aeromonas) were significantly lower than the control group. The cell and challenge experiments showed that BaX030 can significantly increase the expression of C3 and IL8 in the liver and kidney, which decreases the risk of immune organ disease. Moreover, BaX030 effectively reduced the mortality of grass carp. The results revealed that BaX030 can significantly improve the structure of the intestinal flora, enhance immunity and it is beneficial to the control of grass carp Aeromonas.

Effects of Dietary Enterococcus faecalis YFI-G720 on the Growth, Immunity, Serum Biochemical, Intestinal Morphology, Intestinal Microbiota, and Disease Resistance of Crucian Carp (Carassius auratus)

Diseases of crucian carp (Carassius auratus) are closely related to intestinal parameters. Enterococcus faecalis has strong colonization ability in the intestinal tract, and produces natural antibiotics, bacteriocin, and other bacteriostatic substances, which can effectively inhibit some pathogenic bacteria and improve the intestinal microenvironment. This study aimed to assess the effects of E. faecalis YFI-G720 which was isolated from the intestinal of crucian carp on the growth, immunity, intestinal health, and disease resistance of crucian carp. Fish (48.16 ± 0.55 g) were fed four diets, commercial diet or diet containing E. faecalis at 105 CFU/g (EF1), 106 CFU/g (EF2), or 107 CFU/g (EF3) for 28 days. The results showed that supplementation of E. faecalis significantly improved the weight gain ratio (WGR) and the specific growth rate (SGR) compared with control group (p < 0.05). Intestinal mucosal epithelial cells in EF2 were intact and normal, but there was obvious vacuolation in CG. Compared with CG, serum C3 and IgM in EF2 were significantly increased at the end of the experiment (p < 0.05), and serum alkaline phosphatase was significantly higher in all experimental groups (p < 0.05). Among studied immune-related genes, expression was detected by qPCR, C3, IgM, and IL-1βwere upregulated in all experimental groups to varying degrees from 14 days, with highest expression in EF2 at 28 days. Intestinal microbiota structure analyzed through high-throughput sequencing, and the results showed that the relative abundance of Aeromonas and Acinetobacter decreased while Cetobacterium increased in all experimental groups, with the greatest changes in EF2. Challenge tests showed that fish fed E. faecalis were more resistant to Aeromonas veronii (p < 0.05). In conclusion, dietary E. faecalis YFI-G720 at 106 CFU/g can improve the health status, immune parameters, intestinal microbiota composition, and disease resistance of crucian carp.

Grass carp MAP3K4 participates in the intestinal immune response to bacterial challenge

Mitogen-activated protein kinase kinase kinase 4 (MAP3K4) is a multifunctional mediator of the conserved MAPK signaling pathway that plays essential roles in the regulation of immune responses in mammals. However, the function of teleost MAP3K4s in innate immunity, especially in the intestinal immune system, is still poorly understood. In the current study, we identified a fish MAP3K4 homolog (CiMAP3K4) in Ctenopharyngodon idella as well as its immune function in intestine following bacterial infection in vivo and in vitro. The open reading frame (ORF) of CiMAP3K4 encodes putative peptide of 1544 amino acids containing a predicted serine/threonine protein kinase (S_TKc) domain with high identity with other fish MAP3K4s. Phylogenetic analysis revealed the CiMAP3K4 belonged to the fish cluster and showed the closest relationship to Pimephales promelas. Quantitative real-time PCR (qRT-PCR) analysis revealed that CiMAP3K4 transcripts were widely distributed in all tested tissues, especially with high expression in the muscle and intestine of healthy grass carp. In vitro, CiMAP3K4 gene expression was upregulated by bacterial PAMPs (lipolysaccharide (LPS), peptidoglycan (PGN), L-Ala-γ-D-Glu-meso-diaminopimelic acid (Tri-DAP) and muramyl dipeptide (MDP)) and pathogens (Aeromonas hydrophila and Aeromonas veronii) in primary intestinal cells. In vivo, the mRNA expression levels of CiMAP3K4 in the intestine were significantly induced by bacterial MDP challenge in a time-dependent manner; however, this effect could be inhibited by the bioactive dipeptides β-alanyl-l-histidine (carnosine) and alanyl-glutamine (Ala-Gln). Moreover, CiMAP3K4 was located primarily in the cytoplasm, and its overexpression increased the transcriptional activity of AP-1 in HEK293T cells. Collectively, these results suggested that CiMAP3K4 might play an important role in the intestinal immune response to bacterial infections, which paves the way for a better understanding of the intestinal immune system of grass carp.

Potential of Bacillus velezensis as a probiotic in animal feed: a review

Bacillus velezensis is a plant growth-promoting bacterium that can also inhibit plant pathogens. However, based on its properties, it is emerging as a probiotic in animal feed. This review focuses on the potential characteristics of B. velezensis for use as a probiotic in the animal feed industry. The review was conducted by collecting recently published articles from peer-reviewed journals. Google Scholar and PubMed were used as search engines to access published literature. Based on the information obtained, the data were divided into three groups to discuss the (i) probiotic characteristics of B. velezensis, (ii) probiotic potential for fish, and (iii) the future potential of this species to be developed as a probiotic for the animal feed industry. Different strains of B. velezensis isolated from different sources were found to have the ability to produce antimicrobial compounds and have a beneficial effect on the gut microbiota, with the potential to be a candidate probiotic in the animal feed industry. This review provides valuable information about the characteristics of B. velezensis, which can provide researchers with a better understanding of the use of this species in the animal feed industry.

The mutated Bacillus amyloliquefaciens strain shows high resistance to Aeromonas hydrophila and Aeromonas veronii in grass carp

Bacillus amyloliquefaciens X030 (BaX030) has broad-spectrum antibacterial activity against the fish pathogens Aeromonas hydrophila and Aeromonas veronii. To improve its antibacterial effect, BaX030 was subjected to compound mutagenesis of atmospheric and room temperature plasma (ARTP) and nitrosoguanidine (NTG). The results showed that, compared with the original strain, the production of macrolactin A and oxydifficidin in mutated strain N-11 increased to 39 % and 268 %, respectively. The re-sequencing analysis suggested that there were SNPs and InDels in the gene clusters focused on the sucrose utilization pathway, glycolysis pathway and fatty acid synthesis pathway. Scanning electron microscopy revealed that strain N-11 became thin and long. The qRT-PCR results indicated that the expression of immune factors in the liver or kidney tissue of grass carp increased after feeding with N-11. H&E staining and protection experiments also showed that the mortality and surface symptoms of grass carp infected by the two pathogens were significantly reduced. The study identified a probiotic strain with potential application value in aquaculture production and provided a new strategy for the discovery of new strains with higher antibacterial biological activity.

Probiotics in Fish Nutrition—Long-Standing Household Remedy or Native Nutraceuticals?

Over the last decades, aquaculture production increased rapidly. The future development of the industry highly relies on the sustainable utilization of natural resources. The need for improving disease resistance, growth performance, food conversion, and product safety for human consumption has stimulated the application of probiotics in aquaculture. Probiotics increase growth and feed conversion, improve health status, raise disease resistance, decrease stress susceptibility, and improve general vigor. Currently, most probiotics still originate from terrestrial sources rather than fish. However, host-associated (autochthonous) probiotics are likely more persistent in the gastrointestinal tract of fish and may, therefore, exhibit longer-lasting effects on the host. Probiotic candidates are commonly screened in in vitro assays, but the transfer to in vivo assessment is often problematic. In conclusion, modulation of the host-associated microbiome by the use of complex probiotics is promising, but a solid understanding of the interactions involved is only in its infancy and requires further research. Probiotics could be used to explore novel ingredients such as chitin-rich insect meal, which cannot be digested by the fish host alone. Most importantly, probiotics offer the opportunity to improve stress and disease resistance, which is among the most pressing problems in aquaculture.

Mechanisms Used by Probiotics to Confer Pathogen Resistance to Teleost Fish

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

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

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

Marine macroalga-associated heterotroph Bacillus velezensis as prospective therapeutic agent

Marine macroalgae and their accompanying microbial flora were proved to be the reservoir of potential bioactive compounds with promising pharmacological applications. Heterotrophic bacteria concomitant with the marine algae were isolated and screened for their antibacterial potential against clinically recognized pathogens. The bacterial isolate with greater bioactive properties was identified as Bacillus velezensis MBTDLP1 (phylum Firmicutes), which was isolated from the marine macroalga Laurencia papillosa, by integrated morphological, biochemical and molecular characterization. B. velezensis showed promising antibacterial property against methicillin-resistant Staphylococcus aureus and Vibrio parahemolyticus with inhibition zone of 32-36 mm. Organic ethyl acetate extract of the isolate also displayed prospective antibacterial activity against the test pathogens (minimum inhibitory concentration 7.5-15 µg/mL), coupled with promising antioxidant (IC₅₀ 0.1-0.9 mg/mL against oxidants), anti-inflammatory (IC₅₀ 0.01 mg/mL against 5-lipoxygenase), and carbolytic enzyme attenuation properties (IC₅₀ 0.1-0.4 mg/mL in response to α-amylase and α-glucosidase). Significant anticancer potential against breast carcinoma (MCF-7) cells (IC₅₀ 0.03 mg/mL) coupled with lesser cytotoxicity to the normal fibroblast (3T3L) cells (IC₅₀ 0.14 mg/mL) were also recognized. The apoptosis assay could give reasonable outcome as the organic extract of B. velezensis induced apoptosis to 81% of the cancer cells while maintaining almost 60% viability in normal cells. The results put forward that B. velezensis MBTDLP1 could be used to isolate bioactive compounds with therapeutic potential and biomedical applications.

Probiotic supplementation containing Bacillus velezensis enhances expression of immune regulatory genes against pigeon circovirus in pigeons (Columba livia)

AIMS

In this study, we aimed to isolate and evaluate the efficacy of Bacillus velezensis as a probiotic and to assess its activity towards pigeons infected with pigeon circovirus (PiCV).

METHODS AND RESULTS

Bacillus velezensis, isolated from pigeon faeces, was orally administered to pigeons for 60 days. After pigeons were challenged with PiCV, the PiCV viral load and expression of indicator genes for innate immunity were detected in spleen tissue and faeces of pigeons. Bacillus velezensis significantly reduced the PiCV viral load in the faeces and spleen of pigeons 5 days post-challenge (dpc). The mRNA expression levels of treated pigeons showed that interferon-gamma (IFN-γ), myxovirus resistance 1 (Mx1), and signal transducers and activators of transcription 1 (STAT1) genes were upregulated, whereas no expression of interleukin-4 (IL-4) was detected. Moreover, toll-like receptor 2 (TLR2) and 4 (TLR4) were significantly upregulated in probiotic-treated pigeons (P < 0·05).

CONCLUSIONS

This is the first report showing that probiotic supplementation can effectively enhance the T-helper type 1 immune response and decrease the PiCV viral loads in pigeons.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study proposes that the administration of a probiotic strain, B. velezensis, to pigeons can protect against PiCV infection.

Complete genome sequence and antimicrobial activity of Bacillus velezensis JT3-1, a microbial germicide isolated from yak feces

Bacillus velezensis JT3-1 was isolated from feces of the domestic yak (Bos grunniens) in Gansu province of China. Aim to know whether B. velezensis JT3-1 has the potency to be developed as a probiotic bacterium, works on the complete genome sequence, antimicrobial activity, growth performance in calves, and treatment effect on calf diarrhea of B. velezensis JT3-1 were carried out. The results showed that the complete genome of B. velezensis JT3-1 contains one gapless circular chromosome which is 3,929,799 bp, and has 3761 protein-encoding genes with an average GC content of 46.50%. From the antimicrobial activity results, B. velezensis JT3-1 has shown strong antagonistic activities against Listeria monocytogenes, Staphylococcus aureus, Escherichia coli, Salmonella Typhimurium, Mannheimia haemolytica, Staphylococcus hominis, Clostridium perfringens, and Mycoplasma bovis. Compared with the control group, the average weight of the experiment animals from Bv1 group and Bv2 group which were supplemented with B. velezensis JT3-1 was significantly increased (P < 0.05). Meanwhile, the Bv1 and Bv2 supplement significantly improved the level of IgA, IgG, IgM, and IFN-γ in calves as compared with the controls (P < 0.05), but the IL-2 level was not obviously changed between the three groups. In addition, B. velezensis JT3-1 showed a good effect against diarrhea, as the cure rate reached 95.0% (171/180) in newborn calves (Angus cattle) in Xinjiang, and 100.0% (149/149) in yak calves in Qinghai, respectively. Our study will lay a good foundation for the elucidation of the molecular mechanisms of its antimicrobial activity, and supports the hypothesis that JT3-1 has the potential to be developed as a probiotic bacterium in cattle.

Alteration of the gut microbiome and immune factors of grass carp infected with Aeromonas veronii and screening of an antagonistic bacterial strain (Streptomyces flavotricini)

Aeromonas veronii is a widely distributed novel pathogen that can affect humans and animals, it can cause sepsis in fish with high mortality and serious economic losses to aquaculture. In the study, the gut microbiome of the infected and uninfected grass carp with Aeromonas veronii were analyzed probiotics and pathogenic bacteria by the Miseq high-throughput sequencing, the results showed that the infected fish were significantly higher in Proteobacteria, Firmicutes, Fusobacteria, and the immune factors in liver and kidney were up-regulated by qRT-PCR. In order to effectively inhibit the pathogen, we screened an actinomycete strain and had good antibacterial effect on Aeromonas veronii. The new antagonistic bacteria was named as Streptomyces flavotricini X101, the whole genome sequencing revealed that the metabolic process was most active. After grass carp was inoculated with the minimum inhibitory concentration of 900 μg/mL of the strain's fermentation supernatant, then Aeromonas veronii was injected, we found that the pathological symptoms such as body surface, anus and abdominal congestion were alleviated by H&E staining. Cellular experiments showed that it wasn't toxic to liver cells of grass carp. Overall, this is the first study of changes in intestinal flora, phenotype, and immune factors in grass crap infected with Aeromonas veronii, it had important theoretical significance and application value for immunization and prevention.