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

Characterization of microbial contamination in agricultural soil: A public health perspective

Soil is widely recognized as a reservoir of microbial contaminants including antibiotic resistance genes (ARGs) and human bacterial pathogens (HBPs), which are major public health concerns. Although the risks associated with soil safety in different soil habitats have been studied, the results are not comprehensive. In this study, dryland soils used for vegetable, corn, and soybean planting, and submerged soils used for rice planting and crab farming were collected and subjected to metagenomic sequencing to characterize HBPs, ARGs, and virulence factor genes (VFGs). The results showed that submerged soils had a higher abundance of HBP than dryland soils. In addition, the submerged soil microbiome acquired significantly higher levels of high-risk ARGs than the dryland soil microbiome and these ARGs were mainly assigned to bacA, sul1, and aadA genes submerged. Network analysis revealed that 11 HBPs, including Yersinia enterocolitica, Vibrio cholerae, Escherichia coli, and Leptospira interrogans, were high-risk because of their close association with ARGs, VFGs, and mobile genetic elements (MGEs). Procrustes and network analyses showed that HBPs and ARGs were more closely linked in submerged soil. This study confirms that submerged field has higher ecological environment risk and human health risk than dryland soil.

Complete genome analysis of Bacillus velezensis TS5 and its potential as a probiotic strain in mice

Introduction

In recent years, a large number of studies have shown that Bacillus velezensis has the potential as an animal feed additive, and its potential probiotic properties have been gradually explored.

Methods

In this study, Illumina NovaSeq PE150 and Oxford Nanopore ONT sequencing platforms were used to sequence the genome of Bacillus velezensis TS5, a fiber-degrading strain isolated from Tibetan sheep. To further investigate the potential of B. velezensis TS5 as a probiotic strain, in vivo experiments were conducted using 40 five-week-old male specific pathogen-free C57BL/6J mice. The mice were randomly divided into four groups: high fiber diet control group (H group), high fiber diet probiotics group (HT group), low fiber diet control group (L group), and low fiber diet probiotics group (LT group). The H and HT groups were fed high-fiber diet (30%), while the L and LT groups were fed low-fiber diet (5%). The total bacteria amount in the vegetative forms of B. velezensis TS5 per mouse in the HT and LT groups was 1 × 109 CFU per day, mice in the H and L groups were given the same volume of sterile physiological saline daily by gavage, and the experiment period lasted for 8 weeks.

Results

The complete genome sequencing results of B. velezensis TS5 showed that it contained 3,929,788 nucleotides with a GC content of 46.50%. The strain encoded 3,873 genes that partially related to stress resistance, adhesion, and antioxidants, as well as the production of secondary metabolites, digestive enzymes, and other beneficial nutrients. The genes of this bacterium were mainly involved in carbohydrate metabolism, amino acid metabolism, vitamin and cofactor metabolism, biological process, and molecular function, as revealed by KEGG and GO databases. The results of mouse tests showed that B. velezensis TS5 could improve intestinal digestive enzyme activity, liver antioxidant capacity, small intestine morphology, and cecum microbiota structure in mice.

Conclusion

These findings confirmed the probiotic effects of B. velezensis TS5 isolated from Tibetan sheep feces and provided the theoretical basis for the clinical application and development of new feed additives.

Dietary Bacillus velezensis R-71003 and sodium gluconate improve antioxidant capacity, immune response and resistance against Aeromonas hydrophila in common carp

This study aimed to evaluate the effects of dietary supplementation with Bacillus velezensis R-71003 combined with sodium gluconate on antioxidant capacity, immune response and resistance against Aeromonas hydrophila in common carp. In addition, the biocontrol potential of the secondary metabolites of B. velezensis R-71003 was also evaluated to analyze the possible mechanism of B. velezensis R-71003 against A. hydrophila. The results indicated that the antibacterial crude extract of B. velezensis R-71003 can destroy the cell wall of A. hydrophila. Moreover, the results showed that dietary B. velezensis R-71003 could promote antioxidant capacity, which significantly increased the activities of CAT and SOD and decreased the content of MDA. Additionally, B. velezensis R-71003 supplementation significantly enhanced the immunity of common carp, as measured by the mRNA expression levels of cytokine-related genes (TNF-α, TGF-β, IL-1β and IL-10). In addition, dietary B. velezensis R-71003 exhibited an upregulation of IL-10 and a downregulation of IL-1β, coupled with higher survival rates when challenged with A. hydrophila compared to the positive group. Furthermore, compared to prechallenge, the mRNA expression levels of TLR-4, MyD88, IRAK1, TRAF6, TRIF and NF-κB in the head kidney of common carp were significantly increased after challenge. The fish fed the B. velezensis R-71003 diet showed lower expression of TLR-4, MyD88, IRAK1, TRAF6, TRIF and NF-κB after the challenge than those fed the control diet. Thus, this study revealed that B. velezensis R-71003 can improve the resistance of common carp to pathogenic bacteria by destroying bacterial cell walls and improving fish immunity by activating the TLR4 signaling pathway. Importantly, this study indicated that sodium gluconate has a positive effect on B. velezensis R-71003 in enhancing the anti-infection ability of common carp. The results of this study will lay the foundation for the application of B. velezensis R-71003 in combination with sodium gluconate as an alternative to antibiotics in aquaculture.

Autochthonous Bacillus subtilis and Enterococcus faecalis improved liver health, immune response, mucosal microbiota and red-head disease resistance of yellow drum (Nibea albiflora)

Yellow drum (Nibea albiflora), a commercially important fish species in the coastal regions of southeast China, is highly susceptible to red-head disease caused by Vibrio harveyi B0003. Probiotics have been shown to enhance disease resistance in fish, but whether commensal probiotics could improve of the resistance to red-head disease in yellow drum and possible mechanisms has yet not been reported. A six-week feeding trial was conducted to investigate the red-head disease resistance potentials of five probiotic candidates (Bacillus megaterium B1M2, B. subtilis B0E9, Enterococcus faecalis AT5, B. velezensis DM5 and B. siamensis B0E14), and the liver health, serum and skin immunities, gut and skin mucosal microbiota of yellow drum were determined to illustrate the possible mechanisms. The results showed that autochthonous B. subtilis B0E9 and E. faecalis AT5 (particularly E. faecalis AT5, P < 0.05) effectively improved red-head disease resistance in yellow drum. Furthermore, B. subtilis B0E9 and E. faecalis AT5 (particularly E. faecalis AT5) efficiently improve liver health by improving liver morphology and decreasing serum glutamic oxaloacetic transaminase and glutamic propylic transaminase activities pre and post challenged with V. harveyi B0003 (P < 0.05). B. subtilis B0E9 and E. faecalis AT5 led to significant improvement (P < 0.05) in the serum complement 3 content (un-detected after challenged with V. harveyi B0003), lysozyme activity and skin mucosal immunity (such as IL-6, IL-10 and lysozyme expression) pre and post challenged with V. harveyi B0003, which was generally consistent with the cumulative mortality after challenged with V. harveyi B0003. This induced activations of serum and skin mucosal immunities were consistent with the microbiota data showing that B. subtilis B0E9 and E. faecalis AT5 modulated the overall structure of intestinal and skin mucosal microbiota, and in particular, the relative abundance of potentially pathogenic Achromobacter decreased while beneficial Streptococcus, Rothia, and Lactobacillus increased in fish fed with B. subtilis B0E9 and E. faecalis AT5. Overall, autochthonous B. subtilis B0E9 and E. faecalis AT5 (particularly E. faecalis AT5) can improve liver health, serum and skin immunities (especially up-regulated lysozyme activity and inflammation-related genes expression), positively shape gut and skin mucosal microbiota, and enhance red-head disease resistance of yellow drum.

Effects of Dietary Supplementation with Bacillus amyloliquefaciens US573 on Intestinal Morphology and Gut Microbiota of European Sea Bass

Probiotics or direct-fed microbials (DFM) have proven strong potential for improving aquaculture sustainability. This study aims to evaluate the effects of dietary supplementation with the DFM Bacillus amyloliquefaciens US573 on growth performance, intestinal morphology, and gut microbiota (GM) of European sea bass. For this purpose, healthy fish were divided into two feeding trials in triplicate of 25 fish in each tank. The fish were fed with a control basal diet or a DFM-supplemented diet for 42 days. Results showed that, while no significant effects on growth performance were observed, the length and abundance of villi were higher in the DFM-fed group. The benefic effects of DFM supplementation included also the absence of cysts formation and the increase in number of goblet cells playing essential role in immune response. Through DNA metabarcoding analysis of GM, 5 phyla and 14 major genera were identified. At day 42, the main microbiome changes in response to B. amyloliquefaciens US573 addition included the significant decrease in abundance of Actinobacteria phylum that perfectly correlates with a decrease in Nocardia genus representatives which represent serious threat in marine and freshwater fish. On the contrary, an obvious dominance of Betaproteobacteria associated with the abundance in Variovorax genus members, known for their ability to metabolize numerous substrates, was recorded. Interestingly, Firmicutes, particularly species affiliated to the genus Sporosarcina with recent promising probiotic potential, were identified as the most abundant. These results suggest that B. amyloliquefaciens US573 can be effectively recommended as health-promoting DFM in European sea bass farming.

Mucosal and systemic immune effects of Bacillus subtilis in rainbow trout (Oncorhynchus mykiss)

Bacillus spp. are well known for their probiotic properties. Hence, the long-term feeding of Bacillus spp. strains to different fish species has been proved to confer beneficial effects regarding growth or pathogen resistance, among others. However, whether these strains could function as mucosal adjuvants, up-regulating immune responses after a single administration, has not yet been investigated in fish. Thus, in the current work, we have performed a series of experiments in rainbow trout (Oncorhynchus mykiss) aimed at establishing the potential of two Bacillus subtilis spore-forming strains, designated as ABP1 and ABP2, as oral adjuvants/immunostimulants. As an initial step, we evaluated their transcriptional effects on the rainbow trout intestinal epithelial cell line RTgutGC, and in gut tissue explants incubated ex vivo with the two strains. Their capacity to adhere to RTgutGC cells was also evaluated by flow cytometry. Although both strains had the capacity to modulate the transcription of several genes related to innate and adaptive immune responses, it was the ABP1 strain that led to stronger transcriptional effects, also exerting a higher binding capacity to intestinal epithelial cells. Consequently, we selected this strain to establish its effects on splenic B cells upon in vitro exposure as well as to determine the transcriptional effects exerted in the spleen, kidney, and gut after a single oral administration of the bacteria. Our results showed that B. subtilis ABP1 had the capacity to modulate the proliferation, IgM secreting capacity and MHC II surface expression of splenic B cells. Finally, we confirmed that this strain also induced the transcription of genes involved in inflammation, antimicrobial genes, and genes involved in T cell responses upon a single oral administration. Our results provide valuable information regarding how B. subtilis modulates the immune response of rainbow trout, pointing to the usefulness of the ABP1 strain to design novel oral vaccination strategies for aquaculture.

In vitro modulation of gilthead seabream (Sparus aurata L.) leukocytes by Bacillus spp. extracellular molecules upon bacterial challenge

Stimulation of the fish immune system using immunostimulants is an environmentally friendly strategy to minimize bacterial outbreaks in aquaculture. Different biological and synthetic immunostimulants can enhance non-specific innate immune responses by directly activating immune cells. An example are Bacillus spp., known for their immunostimulatory effects, although the exact mechanisms by which Bacillus spp. offer protection against diseases remains to be elucidated. Furthermore, most studies have focused on Bacillus spp. cells, while the immunostimulant effect of their extracellular metabolome, known to harbour biologically important metabolites, including antimicrobial molecules, has been scarcely evaluated. Here, we evaluated the in vitro immune-modulatory properties of extracellular extracts of three Bacillus spp. strains (B. subtilis FI314, B. vezelensis FI436 and B. pumilus FI464), previously isolated from fish-guts and characterized for their in vitro and in vivo antimicrobial activity against a wide range of fish pathogens. Bacillus spp. extracellular extracts did not affect immune cells viability, but remarkably increased pathogens' phagocytosis when seabream head-kidney leukocytes were challenged with Vibrio anguillarum and Edwardsiella tarda. All extracts significantly increased the engulfment of bacterial pathogens 1 h post-infection. Cells stimulated with the extracellular extracts showed an up-regulation of the expression of immune-relevant genes associated with inflammation, including IL-1β, IL-6, and COX-2. In cells challenged with E. tarda, FI314 extracellular extract significantly increased the expression of IL-1β, IL-6, and COX-2, while FI436 and FI464 significantly increased IL-6 expression. The results of this study revealed that the extracellular molecules from Bacillus spp. fish isolates improved the in vitro response of gilthead seabream immune cells and are thus promising candidates to act as immunostimulants, helping fish fight diseases.

Enhanced treatment of organic matter in slaughter wastewater through live Bacillus velezensis strain using nano zinc oxide microsphere

Slaughter wastewater is an important and wide range of environmental issues, and even threaten human health through meat production. A high efficiency and stability microsphere-immobilized Bacillus velezensis strain was designed to remove organic matter and inhibit the growth of harmful bacteria in process of slaughter wastewater. Bacillus velezensis was immobilized on the surface of sodium alginate (SA)/Polyvinyl alcohol (PVA)/Nano Zinc Oxide (Nano-ZnO) microsphere with the adhesion to bio-carrier through direct physical adsorption. Results indicated that SA/PVA/ZnO and SA/ZnO microspheres could inhibit E.coli growth with adding 0.15 g/L nano-ZnO and not affect Bacillus velezensis strain, and the removal the chemical oxygen demand (COD) rates of SA/PVA/ZnO microsphere immobilized cells are 16.99%, followed by SA/ZnO (13.69%) and free bacteria (7.61%) from 50% concentration slaughter wastewater within 24 h at 37 °C, pH 7.0, and 120 rpm, a significant difference was found between the microsphere and control group. Moreover, when the processing time reaches 36 h, COD degradation of SA/PVA/ZnO microsphere is obviously higher than other groups (SA/PVA/ZnO:SA/ZnO:control vs 18.535 : 15.446: 10.812). Similar results were obtained from 30% concentration slaughter wastewater. Moreover, protein degradation assay was detected, and there are no significant difference (SA/PVA/ZnO:SA/ZnO:control vs 35.4 : 34.4: 36.0). The design of this strategy could greatly enhance the degradation efficiency, inhibit the growth of other bacteria and no effect on the activity of protease in slaughter wastewater. These findings suggested that the nano-ZnO hydrogel immobilization Bacillus velezensis system wastewater treatment is a valuable alternative method for the remediation of pollutants from slaughter wastewater with a novel and eco-friendly with low-cost investment as an advantage.

Synergic Effect of Adsorption and Biodegradation by Microsphere Immobilizing Bacillus velezensis for Enhanced Removal Organics in Slaughter Wastewater

Bacterial cell immobilization offers considerable advantages over traditional biotreatment methods using free bacteria. Bacillus velezensis was underwented isolation and genetic identification as COD-degrading bacteria in slaughter wastewaterand immobilized on the surface of polyvinyl alcohol (PVA) microsphere with the adhesion to bio-carrier through direct physical adsorption. The removal CODMn rates of microsphere (PVA) immobilized cells were 16.99%, increased 9.38% from a 50% concentration of slaughter wastewater within 24 h at 37 °C, pH 7.0, and 120 rpm, which was about 2.2 times that of the free bacteria. A significant difference was found in two groups (p < 0.01 p value less than 0.01 means statistical significance), and the COD degradation rate of the microsphere immobilized Bacillus velezensis strain was higher than the control group (PVA: control vs 20.08: 10.81), with the processing time reaching 36 h (p < 0.05). Additionally, similar results were obtained from a 20% concentration of slaughter wastewater within 24 h and 36 h. Moreover, the starch and protein digestibility of the immobilized Bacillus velezensis strain was higher than that of the free bacteria (20.1%: 42.2% vs. 17.5%: 37.2%). These findings revealed that the PVA-bacteria system was a simple, green, and inexpensive process, as well as a promising method. The research goal is aimed to synergize the effects of adsorption and biodegradation, as it can enhance organic removal by immobilized Bacillus velezensis in slaughter wastewater. Moreover, it may be possible that more potential materials can be used as biological carriers for the immobilization of bacterial cells later, which is beneficial for the recycling of resources.