Oral delivery of Bacillus subtilis spores expressing cysteine protease of Clonorchis sinensis to grass carp (Ctenopharyngodon idellus): Induces immune responses and has no damage on liver and intestine function

Inactivation of guanylate kinase in Bacillus sp. TL7-3 cultivated under an optimized ratio of carbon and nitrogen sources influenced GTP regeneration capability and sporulation

Bacillus sp. TL7-3 has potential as a dietary supplement to promote human and animal health. It produces spores that can survive in harsh environments. Thus, when supplemented with nutrients, these spores can withstand the acidic pH of the stomach and resume vegetative development in the gut when exposed to growth-promoting conditions. Spores are formed as a cellular defense mechanism when a culture experiences stress and process optimization to achieve high spore production in a typical batch process remains challenging. Existing literature on the manipulation of gene expression and enzyme activity during batch cultivation is limited. Studies on the growth patterns, morphological changes, and relevant gene expression have aided in enhancing spore production. The present study used the response surface methodology for medium optimization. The model suggested that yeast extract and NH4Cl were significant factors controlling spore production. A comparison between the high weight ratio of carbon and nitrogen (C:N) substrates (8.57:1) in the optimized and basal media (0.52:1) showed an 8.76-fold increase in the final spore concentration. The expression of major genes, including codY, spo0A, kinA, and spo0F, involved in the sporulation was compared when cultivating Bacillus sp. TL7-3 in media with varying C:N ratios. At high C:N ratios, spo0A, kinA, and spo0F were upregulated, whereas codY was downregulated. This led to decreased guanylate kinase activity, resulting in a low guanosine triphosphate concentration and inactivation of CodY, thereby reducing the repression of spo0A and CodY-repressed genes and stimulating sporulation.

Potential effects of probiotics (immunobacteryne; IMB) on growth performance, feed efficacy, blood biochemical, redox balance, nonspecific immunity and heat-shock protein expression of Nile tilapia (Oreochromis niloticus) fingerlings

The supplementation of aquafeed with probiotics is recommended for feasible aquaculture activities. Therefore, the aim of current study was to investigate the potential effects of probiotics on growth performance, feed utilization, biochemical attributes, redox status and immunity response as well as the transcription of heat-shock protein 70 (HSP70) and insulin-like growth factor-1 (IGF-1) genes of Nile tilapia (Oreochromis niloticus; n = 120). Fish with an initial weight of 8.17 ± 0.02 g/fish were randomly divided into four treatment groups and were fed diets containing 0, 0.5, 1 and 1.5 mg immunobacteryne (IMB)/kg diet respectively. Dietary IMB at 1.5 g/kg diet significantly improved the growth performance, feed consumption and growth hormone secretion of the experimental fish (p < 0.05). The 1 or 1.5 g IMB/kg diet boosted phagocytic activities and innate immune response. Serum total protein, total cholesterol, triglycerides and glucose were significantly increased in the groups that were fed 1 and 1.5 mg IMB/kg diet compared to the control (p < 0.05). Meanwhile, the levels of uric acid, creatinine, liver enzymes (aspartate transaminase and alanine transaminase) and cortisol hormone were significantly reduced in the aforementioned treated groups compared to the control (p < 0.05). All fish fed IMB-supplemented diet showed a significant increase in the expression of IGF-1 gene, while the transcription of HSP70 was significantly decreased (p < 0.05). In conclusion, the dietary inclusion of IMB (1 g/kg diet) enhanced growth promoters, feed efficacy, blood biochemical, redox balance and nonspecific immune responses in Nile tilapia fingerlings.

Evaluation of probiotic properties of a Brevibacillus laterosporus strain

Brevibacillus laterosporus is a strain of probiotic bacteria that has been widely used in pest control, cash crop, and other production areas. However, few studies have been conducted on its use as a feed additive in animals. Therefore, the probiotic potential of B. laterosporus PBC01 was evaluated by characterizing hydrophobicity, auto-aggregation activity, bile salt and simulated gastrointestinal fluid tolerance, bienzymatic, and antibacterial activity. Antibiotic susceptibility, hemolysis assays, and supplemental feeding of mice were also performed to evaluate safety features. Our results showed that B. laterosporus PBC01 had moderate hydrophobicity, high auto-agglutination ability. Meanwhile, B. laterosporus PBC01 had good tolerance to bile salt and simulated gastrointestinal fluid. It had the ability to secrete protease, cellulase, and to inhibit various pathogens. In addition, B. laterosporus PBC01 was sensitive to many antibiotics, and did not produce hemolysin. In the safety assessment of mice, it did not cause any deaths, nor did it affect the cell components of blood, antioxidant capacity, and reproductive health. The study indicated the great probiotic characteristics and safety of B. laterosporus PBC01. This may provide a theoretical basis for the clinical application and development of probiotic-based feed additives.

Clonorchiasis and opisthorchiasis: epidemiology, transmission, clinical features, morbidity, diagnosis, treatment, and control

Clonorchis sinensis, Opisthorchis viverrini, and Opisthorchis felineus are important liver flukes that cause a considerable public health burden in eastern Asia, southeastern Asia, and eastern Europe, respectively. The life cycles are complex, involving humans, animal reservoirs, and two kinds of intermediate hosts. An interplay of biological, cultural, ecological, economic, and social factors drives transmission. Chronic infections are associated with liver and biliary complications, most importantly cholangiocarcinoma. With regard to diagnosis, stool microscopy is widely used in epidemiologic surveys and for individual diagnosis. Immunologic techniques are employed for screening purposes, and molecular techniques facilitate species differentiation in reference laboratories. The mainstay of control is preventive chemotherapy with praziquantel, usually combined with behavioral change through information, education and communication, and environmental control. Tribendimidine, a drug registered in the People's Republic of China for soil-transmitted helminth infections, shows potential against both C. sinensis and O. viverrini and, hence, warrants further clinical development. Novel control approaches include fish vaccine and biological control. Considerable advances have been made using multi-omics which may trigger the development of new interventions. Pressing research needs include mapping the current distribution, disentangling the transmission, accurately estimating the disease burden, and developing new diagnostic and treatment tools, which would aid to optimize control and elimination measures.

Current status and progress in the omics of Clonorchis sinensis

Clonorchis sinensis (C. sinensis) is a fish-borne trematode that inhabits the bile duct of mammals including humans, cats, dogs, rats, and so on. In the complex life cycle of C. sinensis, the worm develops successively in two intermediate hosts in fresh water and one definitive host. What's more, it undergoes eight developmental stages with a distinct morphology. Clonorchiasis, caused by C. sinensis infection, is an important food-borne parasitic disease and one of the most common zoonoses. C. sinensis infection could result in hyperplasia of the bile duct epithelium, obstructive jaundice, gall-stones, cholecystitis and cholangitis, even liver cirrhosis and cholangiocarcinoma. Thus, clonorchiasis is a serious public health problem in endemic areas. Integrated strategies should be adopted in the prevention and control of clonorchiasis due to the epidemiological characteristics. The recent advances in high-throughput technologies have made available the profiling of multiple layers of a biological system, genomics, transcriptomics, proteomics, and metabolomics. These data can help us to get more information about the development, physiology, metabolism, and reproduction of the parasite as well as pathogenesis and parasite-host interactions in clonorchiasis. In the present study, we summarized recent progresses in omics studies on C. sinensis providing insights into the studies and future directions on treating and preventing C. sinensis associated diseases.

Oral immunizations with Bacillus subtilis spores displaying VP19 protein provide protection against Singapore grouper iridovirus (SGIV) infection in grouper

Disease caused by Singapore grouper iridovirus (SGIV) results in major economic losses in the global grouper aquaculture industry. Vaccination is considered to be the most effective way to protect grouper from SGIV. In this study, the spores of Bacillus subtilis (B.subtilis) WB600 were utilized as the vehicle that the VP19 protein was displayed on the spores surface. To further investigate the effect of oral vaccination, the grouper were orally immunized with B.s-CotC-19 spores. After challenged, the survival rate of grouper orally vaccinated with B.s-CotC-19 spores was 34.5% and the relative percent survival (RPS) was 28.7% compared to the PBS group. Moreover, the viral load in the tissues of the B.s-CotC-19 group was significantly lower than that of the PBS group. The histopathological sections of head kidney and liver tissue from the B.s-CotC-19 group showed significantly less histopathology compared to the PBS group. In addition, the specific IgM levels in serum in the B.s-CotC-19 group was higher than those in the PBS group. In the hindgut tissue, the immune-related gene expression detected by quantitative real-time PCR (qRT-PCR) exhibited an increasing trend in different degrees in the B.s-CotC-19 group, suggesting that the innate and adaptive immune responses were activated. These results indicated that the oral administration of recombinant B.subtilis spores was effective for preventing SGIV infection. This study provided a feasible strategy for the controlling of fish virus diseases.

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.

The recombinant subunit vaccine encapsulated by alginate-chitosan microsphere enhances the immune effect against Micropterus salmoides rhabdovirus

The disease caused by Micropterus salmoides rhabdovirus (MSRV) has brought substantial economic losses to the largemouth bass aquaculture industry in China. Vaccination was considered as a potential way to prevent and control this disease. As a kind of sustained and controlled release system, alginate and chitosan microspheres (SA-CS) are widely used in the development of oral vaccination for fish. Here, we prepared a king of alginate-chitosan composite microsphere to encapsulate the second segment of MSRV glycoprotein (G2 protein) and then evaluated the immune effect of the microsphere vaccine on largemouth bass. Largemouth bass were vaccinated via intragastric immunization by different treatments (PBS, SA-CS, G2 and SA-CS-G2). The results showed that a stronger immune response including serum antibody levels, immune-related physiological indexes (acid phosphatase, alkaline phosphatase, superoxide dismutase and total antioxidant capacity) and the expression of immune-related gene (IgM、IL-8、IL-1β、CD4、TGF-β、TNF-α) can be induced obviously with SA-CS-G2 groups compared with G2 groups when fish were vaccinated. Furthermore, fish were injected with a lethal dose of MSRV after immunization for 28 days, and the highest relative percentage survival (54.8%) was observed in SA-CS-G2 group (40 μg per fish), which is significantly higher than that of G2 group (25.8%). This study showed that alginate-chitosan microspheres as the vaccine carrier can effectively improve the immune effect of oral vaccination and induce better immune protection effect against MSRV infection.

Surface Display of porcine circovirus type 2 antigen protein cap on the spores of bacillus subtilis 168: An effective mucosal vaccine candidate

The oral mucosal vaccine has great potential in preventing a series of diseases caused by porcine circovirus type 2 (PCV2) infection. This study constructed a recombinant Bacillus subtilis RB with PCV2 Capsid protein (Cap) on its spore surface and cotB as a fusion partner. The immune properties of the recombinant strain were evaluated in a mouse model. IgA in intestinal contents and IgG in serum were detected by enzyme-linked immunosorbent assay (ELISA). The results demonstrated that recombinant spores could activate strong specific mucosal and humoral immune responses. In addition, spores showed good mucosal immune adjuvant function, promoting the proliferation of CD3+, CD4+ and CD8+ T cells and other immune cells. We also found that the relative expression of inflammatory cytokines such as IL-1β, IL-6, IL-10, TNF-α and IFN in the small intestinal mucosa was significantly up-regulated under the stimulation of recombinant bacteriophage. These effects are important for the balance of Th1/Th2-like responses. In summary, our results suggest that recombinant B. subtilis RB as a feed additive provides a new strategy for the development of novel and safe PCV2 mucosal subunit vaccines.

Bacillus subtilis Expressing the Infectious Pancreatic Necrosis Virus VP2 Protein Retains Its Immunostimulatory Properties and Induces a Specific Antibody Response

Bacillus subtilis has been documented in the past years as an effective probiotic for different aquacultured species, with recognized beneficial effects on water quality, fish growth and immune status. Furthermore, its potential as a vaccine adjuvant has also been explored in different species. In the current work, we have used B. subtilis spores as delivery vehicles for the presentation of the VP2 protein from infectious pancreatic necrosis virus (IPNV). For this, the VP2 gene was amplified and translationally fused to the crust protein CotY. The successful expression of VP2 on the spores was confirmed by Western blot. We then compared the immunostimulatory potential of this VP2-expressing strain (CRS208) to that of the original B. subtilis strain (168) on rainbow trout (Oncorhynchus mykiss) leukocytes obtained from spleen, head kidney and the peritoneal cavity. Our results demonstrated that both strains significantly increased the percentage of IgM⁺ B cells and the number of IgM-secreting cells in all leukocyte cultures. Both strains also induced the transcription of a wide range of immune genes in these cultures, with small differences between them. Importantly, specific anti-IPNV antibodies were detected in fish intraperitoneally or orally vaccinated with the CRS208 strain. Altogether, our results demonstrate B. subtilis spores expressing foreign viral proteins retain their immunomodulatory potential while inducing a significant antibody response, thus constituting a promising vaccination strategy.

Molecular Mechanisms of Clonorchis sinensis-Host Interactions and Implications for Vaccine Development

Infections caused by Clonorchis sinensis remain a significant public health challenge for both humans and animals, causing pyogenic cholangitis, cholelithiasis, cholecystitis, biliary fibrosis, and even cholangiocarcinoma. However, the strategies used by the parasite and the immunological mechanisms used by the host have not yet been fully understood. With the advances in technologies and the accumulated knowledge of host-parasite interactions, many vaccine candidates against liver flukes have been investigated using different strategies. In this review, we explore and analyze in-depth the immunological mechanisms involved in the pathogenicity of C. sinensis. We highlight the different mechanisms by which the parasite interacts with its host to induce immune responses. All together, these data will allow us to have a better understanding of molecular mechansism of host-parasite interactions, which may shed lights on the development of an effective vaccine against C. sinensis.

Oral Administration of Bacillus subtilis Subunit Vaccine Significantly Enhances the Immune Protection of Grass Carp against GCRV-II Infection

Grass carp reovirus (GCRV) is a severe virus that causes great losses to grass carp culture every year, and GCRV-II is the current popular and fatal strain. VP56, fibrin on the outer surface of GCRV-II, mediates cell attachment. In this study, we firstly divided the VP56 gene into four fragments to screen the optimal antigen by enzyme-linked immunosorbent assay and neutralizing antibody methods. The second fragment VP56-2 demonstrates the optimal efficiency and was employed as an antigen in the following experiments. Bacillus subtilis were used as a carrier, and VP56-2 was expressed on the surface of the spores. Then, we performed the oral immunization for grass carp and the challenge with GCRV-II. The survival rate was remarkably raised, and mRNA expressions of IgM were significantly up-regulated in spleen and head kidney tissues in the B. s-CotC-VP56-2 group. Three crucial immune indexes (complement C3, lysozyme and total superoxide dismutase) in the sera were also significantly enhanced. mRNA expressions of four important genes (TNF-α, IL-1β, IFN1 and MHC-II) were significantly strengthened. Tissue lesions were obviously attenuated by histopathological slide examination in trunk kidney and spleen tissues. Tissue viral burdens were significantly reduced post-viral challenge. These results indicated that the oral recombinant B. subtilis VP56-2 subunit vaccine is effective for controlling GCRV infection and provides a feasible strategy for the control of fish virus diseases.

Prospects for liver fluke vaccines

Fasciola spp., Opisthorchis spp. and Clonorchis sinensis are common liver flukes that can cause a variety of diseases, mainly cholangiocarcinoma induced by clonorchiasis and liver damage and associated pathology induced by fascioliasis. Because these trematodes are parasites of humans and domestic animals, they have greatly affected the economy of agricultural industries and public health worldwide. Due to the emergence of drug resistance and the living habits of flukes, among other reasons, a possibility of reinfection remains even when antiparasitic drugs are used. Therefore, developing a safe, efficient and cost-effective vaccine against trematodes is an important goal. Here, we briefly describe the progress in the development of vaccines against liver flukes. Related innovations may provide effective protection against these helminths and the diseases that they cause.

Orally Administered Bacillus Spores Expressing an Extracellular Vesicle-Derived Tetraspanin Protect Hamsters Against Challenge Infection With Carcinogenic Human Liver Fluke

BACKGROUND

The human liver fluke Opisthorchis viverrini is a food-borne trematode that causes hepatobiliary disease in humans throughout Southeast Asia. People become infected by consuming raw or undercooked fish containing metacercariae. Development of a vaccine to prevent or minimize pathology would decrease the risk of severe morbidity, including the development of bile duct cancer.

METHODS

We produced an oral vaccine based on recombinant Bacillus subtilis spores expressing the large extracellular loop (LEL) of O. viverrini tetraspanin-2 (Ov-TSP-2), a protein that is abundant on the surface of O. viverrini secreted extracellular vesicles (EVs). Recombinant spores expressing Ov-TSP-2-LEL were orally administered to hamsters prior to challenge infection with O. viverrini metacercariae.

RESULTS

Vaccinated hamsters generated serum IgG as well as bile IgG and IgA responses to Ov-TSP-2-LEL, and serum IgG from vaccinated hamsters blocked the uptake of fluke EVs by a human bile duct epithelial cell line. Vaccinated hamsters had 56% reductions in both adult flukes and fecal eggs compared to the control group.

CONCLUSIONS

These findings indicate that oral vaccination of hamsters with recombinant B. subtilis spores expressing Ov-TSP-2-LEL is efficacious at reducing infection intensity and could form the basis of a vaccine for control of carcinogenic liver fluke infection in humans.

The storage stability of Bacillus subtilis spore displaying cysteine protease of Clonorchis sinensis and its effect on improving the gut microbiota of mice

Bacillus subtilis (B. subtilis) spore can serve as an ideal vehicle for expressing heterologous antigens, and elicit specific immune responses by oral administration. In previous studies, we successfully constructed the recombinant B. subtilis spores expressing cysteine protease of Clonorchis sinensis (C. sinensis, B.s-CsCP), and confirmed that oral administration of B.s-CsCP could elicit good protective immune responses in mice. In this study, Gram staining was used to observe the morphology of B.s-CsCP in different form, and the storage of liquid spores and lyophilized spores at different temperatures was compared. The mice were orally immunized with three different doses of spores (2×10⁸, 1×10⁹, and 5×10⁹ CFU/day) for three times in total at biweekly interval. Then, antibody levels of mice were measured, the safety of spores was evaluated, and the changes of gut microbiota after oral gavage of spores (1×10⁹ dose) were investigated. Results showed that B. subtilis was a typical Gram-positive bacterium, and its spore had good resistance to chemical dye. Liquid B. subtilis spores resuspended in sterile water could be stored for a long time at 4 °C or below, while lyophilized spores could be well stored even at RT and better at lower temperatures. Oral administration of B. subtilis spores to mice could stimulate both local mucosal and systemic immune responses in a dose-dependent manner without toxic side effects. Besides, beneficial bacteria producing butyrate such as Odoribacter were increased, while potential pathogens such as Escherichia-Shigella were decreased in mice intestine. Therefore, our work further confirmed that B. subtilis spores expressing CsCP could be a promising oral vaccine against C. sinensis with the advantages of stability, safety, easy storage, and promotion of intestinal health.Key Points• Recombinant CsCP B. subtilis spores could be easily preserved in either liquid or freeze-dried state.• Oral immunization of recombinant spores in mice could increase both local and system immune levels in a dose-dependent manner.• Oral administration of recombinant spores increased the number of beneficial bacteria and reduced the number of harmful bacteria in the intestinal tract of mice.

Surface display of spring viremia of carp virus glycoprotein on Lactococcus lactis and its protection efficacy in common carp (Cyprinus carpio L.)

Spring viremia of carp virus (SVCV) causes devastating disease in aquaculture, resulting in significant economic impact. To develop an effective means against SVCV infection, a Lactococcus lactis (L.lactis) based subunit vaccine (pNZ-UGA) was developed based on surface displaying of SVCV glycoprotein using anchoring motif of the cA (C terminus of the peptidoglyvsn-binding) domains of AcmA, a major autolysin from L.lactis. The surface expression of SVCV glycoprotein was verified by indirect immunofluorescence assay. The efficacy of the constructed vaccine was further evaluated in common carp. The results showed that the higher levels of specific IgM could be detected in fish vaccinated with pNZ-UGA, compared with that in PBS and L.lactis groups. Immune-related genes including TNF-α, IL-6b, IL-1β, Cxcr 1, Cxca, IFNg2b, I-IFN, and IgM expression in pNZ-UGA group were strongly up-regulated, revealing that robust innate immune response was induced. Notably, the lowest cumulative mortality (13.46%) was observed in fish vaccinated with pNZ-UGA vaccine after SVCV challenge, whereas the cumulative mortality were 100.00% and 92.31% in PBS and L.lactis groups, respectively. This study suggests the potential use of the recombinant L.lactis with surface displaying antigen proteins as effective vaccines against SVCV and other fish virus infection.

Assessment of control strategies against Clonorchis sinensis infection based on a multi-group dynamic transmission model

Clonorchiasis is one of the most important food-borne trematodiases affecting millions of people. Strategies were recommended by different organizations and control programmes were implemented but mostly in short-time periods. It's important to assess the long-term benefits and sustainability of possible control strategies on morbidity control of the disease. We developed a multi-group transmission model to describe the dynamics of C. sinensis transmission among different groups of people with different raw-fish-consumption behaviors, based on which, a full model with interventions was proposed and three common control measures (i.e., preventive chemotherapy, information, education, and communication (IEC) and environmental modification) and their possible combinations were considered. Under a typical setting of C. sinensis transmission, we simulated interventions according to different strategies and with a series of values of intervention parameters. We found that combinations of measures were much beneficial than those singly applied; higher coverages of measures had better effects; and strategies targeted on whole population performed better than that on at-risk population with raw-fish-consumption behaviors. The strategy recommended by the government of Guangdong Province, China shows good and sustainable effects, under which, the infection control (with human prevalence <5%) could be achieved within 7.84 years (95% CI: 5.78-12.16 years) in our study setting (with original observed prevalence 33.67%). Several sustainable strategies were provided, which could lead to infection control within 10 years. This study makes the effort to quantitatively assess the long-term effects of possible control strategies against C. sinensis infection under a typical transmission setting, with application of a multi-group dynamic transmission model. The proposed model is easily facilitated with other transmission settings and the simulation outputs provide useful information to support the decision-making of control strategies on clonorchiasis.

Progress in research and application development of surface display technology using Bacillus subtilis spores

Bacillus subtilis is a widely distributed aerobic Gram-positive species of bacteria. As a tool in the lab, it has the advantages of nonpathogenicity and limited likelihood of becoming drug resistant. It is a probiotic strain that can be directly used in humans and animals. It can be induced to produce spores under nutrient deficiency or other adverse conditions. B. subtilis spores have unique physical, chemical, and biochemical characteristics. Expression of heterologous antigens or proteins on the surface of B. subtilis spores has been successfully performed for over a decade. As an update and supplement to previously published research, this paper reviews the latest research on spore surface display technology using B. subtilis. We have mainly focused on the regulation of spore coat protein expression, display and application of exogenous proteins, and identification of developing research areas of spore surface display technology.

Oral delivery of Bacillus subtilis spores expressing Clonorchis sinensis paramyosin protects grass carp from cercaria infection

Clonorchis sinensis (C. sinensis), an important fishborne zoonotic parasite threatening public health, is of major socioeconomic importance in epidemic areas. Effective strategies are still urgently expected to prevent against C. sinensis infection. In the present study, paramyosin of C. sinensis (CsPmy) was stably and abundantly expressed on the surface of Bacillus subtilis spores. The recombinant spores (B.s-CotC-CsPmy) were incorporated in the basal pellets diet in three different dosages (1 × 10⁵, 1 × 10⁸, 1 × 10¹¹ CFU/g pellets) and orally administrated to grass carp (Ctenopharyngodon idella). The immune responses and intestinal microbiota in the treated grass carp were investigated. Results showed that specific anti-CsPmy IgM levels in sera, skin mucus, bile, and intestinal mucus, as well as mRNA levels of IgM and IgZ in the spleen and head kidney, were significantly increased in B.s-CotC-CsPmy-10¹¹ group. Besides, transcripts levels of IL-8 and TNF-αin the spleen and head kidney were also significantly elevated than the control groups. Moreover, mRNA levels of tight junction proteins in the intestines of B.s-CotC-CsPmy-10¹¹ group increased. Potential pathogenetic bacteria with lower abundance and higher abundances of candidate probiotics and bacteria associated with digestion in 1 × 10¹¹ CFU/g B.s-CotC-CsPmy spores administrated fishes could be detected compared with control group. The amount of metacercaria in per gram fish flesh was statistically decreased in 1 × 10¹¹ CFU/g B.s-CotC-CsPmy spores orally immunized group. Our work demonstrated that B. subtilis spores presenting CsPmy on the surface could be a promising effective, safe, and needle-free candidate vaccine against C. sinensis infection for grass carp.

Bacillus subtilis, an ideal probiotic bacterium to shrimp and fish aquaculture that increase feed digestibility, prevent microbial diseases, and avoid water pollution

Beneficial microorganisms maintain the ecosystems, plants, animals and humans working in healthy conditions. In nature, around 95% of all microorganisms produce beneficial effects by increasing nutrients digestion and assimilation, preventing pathogens development and by improving environmental parameters. However, increase in human population and indiscriminate uses of antibiotics have been exerting a great pressure on agriculture, livestock, aquaculture, and also to the environment. This pressure has induced the decomposition of environmental parameters and the development of pathogenic strains resistant to most antibiotics. Therefore, all antibiotics have been restricted by corresponding authorities; hence, new and healthy alternatives to prevent or eliminate these pathogens need to be identified. Thus, probiotic bacteria utilization in aquaculture systems has emerged as a solution to prevent pathogens development, to enhance nutrients assimilation and to improve environmental parameters. In this sense, B. subtilis is an ideal multifunctional probiotic bacterium, with the capacity to solve these problems and also to increase aquaculture profitability.

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

Aeromonas veronii is an emerging aquatic pathogen causing hemorrhagic septicemia in humans and animals. Probiotic is an effective strategy for controlling enteric infections through reducing intestinal colonization by pathogens. Here we report that the consumption of Bacillus velezensis regulated the intestinal innate immune response and decreased the degree of intestinal inflammation damage caused by the A. veronii in Crucian carp. In this study, we isolated four strains of B. velezensis, named C-11, S-22, L-17 and S-14 from apparently healthy Crucian carp, which exerted a broad-spectrum antimicrobial activity inhibiting both Gram-positive and Gram-negative bacteria especially the fish pathogens. B. velezensis isolates showed typical Bacillus characteristics by endospore staining, physiological and biochemical test, enzyme activity analysis (amylase, protease, and lipase), and molecular identification. Here, Bacillus-containing dietary was orally administrated to Crucian carp for 8 weeks before A. veronii challenge. Immunological parameters and the expression of immune-related genes were measured at 2, 4, 6, 8, and 10 weeks post-administration. The results showed that B. velezensis was found to promote the increase in the phagocytic activities of peripheral blood leukocytes (PBLs) and head kidney leukocytes (HKLs), as well as the increase in interleukin 1β (IL-1β), IL-10 and tumor necrosis factor α (TNF-α) concentration of serum. Lysozyme levels (113.76 U/mL), ACP activity (25.32 U/mL), AKP activity (130.08 U/mL), and SOD activity (240.63 U/mL) were maximum (P < 0.05) in the B. velezensis C-11 treated group at 8 week. Our results showed that Crucian carp fed with the diet containing B. velezensis C-11 and S-22 developed a strong immune response with significantly higher (P < 0.05) levels of IgM in samples of serum, mucus of skin and intestine compared to B. velezensis L-17 and S-14 groups. Moreover, B. velezensis spores appeared to show no toxicity and damage in fish, which could inhabit the gut of Crucian carp. B. velezensis restrained up-regulation of pro-inflammation cytokines (IL-1β, IFN-γ, and TNF-α) mRNA levels in the intestine and head kidney at final stage of administration, and the expression of IL-10 was increased throughout the 10-week trial. A. veronii infection increased the population of inflammatory cells in the intestinal villi in the controls. In contrast, numerous goblet cells and few inflammatory cells infiltrated the mucosa in the B. velezensis groups after challenge with A. veronii. Compared with A. veronii group, B. velezensis could safeguard the integrity of intestinal villi. The highest post-challenge survival rate (75.0%) was recorded in B. velezensis C-11 group. The present data suggest that probiotic B. velezensis act as a potential gut-targeted therapy regimens to protecting fish from pathogenic bacteria infection.

IMPORTANCE

In this work, four Bacillus velezensis strains isolated from apparently healthy Crucian carp, which exhibited a broad-spectrum antibacterial activity especially the fish pathogens. Administration of B. velezensis induced the enhancement of the intestinal innate immune response through reducing intestinal colonization by pathogens. The isolation and characterization would help better understand probiotic can be recognized as an alternative of antimicrobial drugs protecting human and animal health.

Oral delivery of Bacillus subtilis spores expressing grass carp reovirus VP4 protein produces protection against grass carp reovirus infection

Grass carp (Ctenopharyngodon idellus) hemorrhagic disease (GCHD), caused by grass carp reovirus (GCRV), has given rise to an enormous loss in grass carp industry during the past years. Up to date, vaccination remained to be the most effective way to protect grass carp from GCHD. Oral vaccination is of major interest due to its advantages of noninvasive, time-saving, and easily-operated. The introduction of oral vaccination has profound impact on aquaculture industry because of its feasibility of extensive application for fish in various size and age. However, the main challenge in developing oral vaccine is that antigens are easily degraded and are easy to induce tolerance. Bacillus subtilis (B. subtilis) spores would be an ideal oral vaccine delivery system for their robust specialty, gene operability, safety and adjuvant property. VP4 protein is the major outer capsid protein encoded by GCRV segment 6 (S6), which plays an important role in viral invasion and replication. In this study, we used B. subtilis spores as the oral delivery system and successfully constructed the B. subtilis CotC-VP4 recombinant spores (CotC-VP4 spores) to evaluate its protective efficacy in grass carp. Grass carp orally immunized with CotC-VP4 spores showed a survival rate of 57% and the relative percent survival (RPS) of 47% after the viral challenge. Further, the specific IgM levels in serum and the specific IgZ levels in intestinal mucus were significantly higher in the CotC-VP4 group than those in the Naive group. The immune-related genes including three innate immune-related genes (IL-4/13A, IL-4/13B, CSF1R), four adaptive immune-related genes (BAFF, CD4L, MHC-II, CD8), three inflammation-related genes (IL-1β, TNF-α, TGF-β) and interferon type I (IFN-I) related signaling pathway genes were significantly up-regulated in the CotC-VP4 group. The study demonstrated that the CotC-VP4 spores produced protection in grass carp against GCRV infection, and triggered both innate and adaptive immunity post oral immunization. This work highlighted that Bacillus subtilis spores were powerful platforms for oral vaccine delivery, and the combination of Bacillus subtilis spores with GCRV VP4 protein was a promising oral vaccine.

Oral Immunization with Nontoxigenic Clostridium difficile Strains Expressing Chimeric Fragments of TcdA and TcdB Elicits Protective Immunity against C. difficile Infection in Both Mice and Hamsters

The symptoms of Clostridium difficile infection (CDI) are attributed largely to two C. difficile toxins, TcdA and TcdB. Significant efforts have been devoted to developing vaccines targeting both toxins through parenteral immunization routes. However, C. difficile is an enteric pathogen, and mucosal/oral immunization would be particularly useful to protect the host against CDI, considering that the gut is the main site of disease onset and progression. Moreover, vaccines directed only against toxins do not target the cells and spores that transmit the disease. Previously, we constructed a chimeric vaccine candidate, mTcd138, comprised of the glucosyltransferase and cysteine proteinase domains of TcdB and the receptor binding domain of TcdA. In this study, to develop an oral vaccine that can target both C. difficile toxins and colonization/adhesion factors, we expressed mTcd138 in a nontoxigenic C. difficile (NTCD) strain, resulting in strain NTCD_mTcd138. Oral immunization with spores of NTCD_mTcd138 provided mice full protection against infection with a hypervirulent C. difficile strain, UK6 (ribotype 027). The protective strength and efficacy of NTCD_mTcd138 were further evaluated in the acute CDI hamster model. Oral immunization with spores of NTCD_mTcd138 also provided hamsters significant protection against infection with 2 × 10⁴ UK6 spores, a dose 200-fold higher than the lethal dose of UK6 in hamsters. These results imply that the genetically modified, nontoxigenic C. difficile strain expressing mTcd138 may represent a novel mucosal vaccine candidate against CDI.

Molecular cloning and functional characterization of cathepsin B from Nile tilapia (Oreochromis niloticus)

Cathepsin B (CatB) has been widely known for its hydrolytic ability and involvement in the innate immunity. However, the mechanism of CatB from teleosts participating in immunoregulation remains poorly understood; and the sequence of CatB from Nile tilapia (NtCatB) has not been cloned and characterized. In this study, the coding sequence of NtCatB was cloned, and then characterized by bioinformatic analysis and heterologous expression. The deduced amino acid sequence (330-aa) of NtCatB contains the representative features of CatB. Quantitative real-time PCR revealed the extensive mRNA expression of NtCatB in six tissues of healthy Nile tilapia, and its transcription level was significantly up-regulated after Streptococcus agalactiae challenge. NtCatB may interact with some immunological function proteins and take part in the regulatory pathway. These results suggest that NtCatB is likely to be involved in the immune reaction. The mature region (residues 79-328, mNtCatB) of NtCatB was cloned and transferred to pET-28a for expressing the recombinant protein. The purified recombinant mNtCatB was verified with the activity of 992.34 U mg^-1 min^-1 under the optimal condition using a substrate hydrolyzing assay. The recombinant cystatin-A1-like can effectively inhibit the activity of the recombinant mNtCatB, and their binding form was predicted by molecular docking. Our results contribute to elucidating the immunological functions of NtCatB.