Mixed Bacillus Species Enhance the Innate Immune Response and Stress Tolerance in Yellow Perch Subjected to Hypoxia and Air-Exposure Stress

Integrated mRNA and miRNA analysis reveals the regulatory network of oxidative stress and inflammation in Coilia nasus brains during air exposure and salinity mitigation

BACKGROUND

Air exposure is an inevitable source of stress that leads to significant mortality in Coilia nasus. Our previous research demonstrated that adding 10‰ NaCl to aquatic water could enhance survival rates, albeit the molecular mechanisms involved in air exposure and salinity mitigation remained unclear. Conversely, salinity mitigation resulted in decreased plasma glucose levels and improved antioxidative activity. To shed light on this phenomenon, we characterized the transcriptomic changes in the C. nasus brain upon air exposure and salinity mitigation by integrated miRNA-mRNA analysis.

RESULTS

The plasma glucose level was elevated during air exposure, whereas it decreased during salinity mitigation. Antioxidant activity was suppressed during air exposure, but was enhanced during salinity mitigation. A total of 629 differentially expressed miRNAs (DEMs) and 791 differentially expressed genes (DEGs) were detected during air exposure, while 429 DEMs and 1016 DEGs were identified during salinity mitigation. GO analysis revealed that the target genes of DEMs and DEGs were enriched in biological process and cellular component during air exposure and salinity mitigation. KEGG analysis revealed that the target genes of DEMs and DEGs were enriched in metabolism. Integrated analysis showed that 24 and 36 predicted miRNA-mRNA regulatory pairs participating in regulating glucose metabolism, Ca2+ transport, inflammation, and oxidative stress. Interestingly, most of these miRNAs were novel miRNAs.

CONCLUSION

In this study, substantial miRNA-mRNA regulation pairs were predicted via integrated analysis of small RNA sequencing and RNA-Seq. Based on predicted miRNA-mRNA regulation and potential function of DEGs, miRNA-mRNA regulatory network involved in glucose metabolism and Ca2+ transport, inflammation, and oxidative stress in C. nasus brain during air exposure and salinity mitigation. They regulated the increased/decreased plasma glucose and inhibited/promoted antioxidant activity during air exposure and salinity mitigation. Our findings would propose novel insights to the mechanisms underlying fish responses to air exposure and salinity mitigation.

Hematological changes in Florida pompano (Trachinotus carolinus) supplemented with β-glucan and Pediococcus acidilactici synbiotic

Florida pompano (Trachinotus carolinus) are a species of growing interest for commercial aquaculture. Effective health monitoring is crucial to the successful growout of the species, and prophylactic and therapeutic use of chemicals and antibiotics has been the traditional strategy for promoting stock health. However, concerns about antimicrobial resistance, chemical residues in seafood products and the environment, and resultant immunosuppression have prompted the industry to identify alternative management strategies, including supplementation with prebiotics, probiotics, and combinations of both (synbiotics). The objectives of this study are to determine and compare hematological, plasma biochemical, and plasma protein electrophoresis data of synbiotic-supplemented (β-glucan and Pediococcus acidilactici) and non-supplemented Florida pompano. Reference intervals for blood analytes are provided for both groups and for subgroups (females, males, large, and small fish) where statistically significant results exist. There are no differences between the hematological and plasma biochemistry analytes between the supplemented and control groups, except for blood urea nitrogen and carbon dioxide, indicating a possible effect of synbiotic supplementation on gill function and osmoregulation. Sex-related and size-related differences are observed within each of the control and supplemented groups; however, biometric measurements do not strongly correlate with blood analytes. These data represent baseline hematological and plasma biochemical data in the Florida pompano and indicate the safety of synbiotic supplementation in this commercially important species. This study serves to further the commercialization of Florida pompano by providing blood analyte reference intervals for health monitoring in the aquaculture setting.

Beneficial effects of indigenous Bacillus spp. on growth, antioxidants, immunity and disease resistance of Rhynchocypris lagowskii

This study aimed to investigate the effect of Bacillus aryabhattai (LSG3-7) and Bacillus mojavensis (LSG3-8) on growth performance, antioxidant capacity, and immune response in Rhynchocypris lagowskii (Dybowski, 1869), at the trial and challenge periods. A 630 healthy fish (10.76 ± 0.05) were randomly divided into six groups: control group (D1) was fed the basal diet, D2 and D3 were supplemented with LSG 3-7 and LSG3-8 (1 × 108 CFU/g) for both of them, whereas D4 was supplemented with a mixture of both bacteria (0.5 × 108 CFU/g each), and D5 was supplemented with LSG3-7 0.75 × 108 CFU/g + LSG3-8 0.25 × 108 CFU/g, and D6 supplemented with LSG3-7 0.25 × 108 CFU/g + LSG3-8 0.75 × 108 CFU/g. After the trial, Aeromonas hydrophila was used in a challenge test for 14 days. Treatments showed significant differences (p < 0.05) in growth performance and antioxidant capacity (CAT, CuZn-SOD, GPX) in the liver and intestine compared to the control. The antioxidant-related genes CAT, CuZn-SOD, GPX, and Nrf2 in the liver and intestine showed upregulation compared with the control group. Serum IgM, LZM, C3, C4, and AKP showed a favorable superiority (p < 0.05) in treatments (D2 - D6) at the trial and challenge test compared to controls. In parallel, immune-related genes (IgM, NF-κB, TLR-1, TLR-2, and MyD88) showed an up-regulated level (p < 0.05) in treatments (D2 - D6) compared to the control. In addition, pro-inflammatory cytokines (IL-1, TNF-α) showed a downregulated level in treatments (D2 - D6). After the challenge test, the immune-related genes in the liver and muscle showed an up-regulated level in treatments compared to the controls. The survival rate showed a significant increase (p < 0.05) in the treatment groups (D2 - D6) compared to the control. Overall, individuals and the bacterial mixture of B. aryabhattai and B. mojavensis could improve the growth performance, antioxidant capacity, immune capacity, and survival rate of R. lagowskii and prevent side effects of A. hydrophila. However, B. mojavensis showed a slight improvement compared to B. aryabhattai without a significant difference between them.

Replacement Effect of Fish Meal by Plant Protein Sources in Olive Flounder (Paralichthys olivaceus) Feeds with an Addition of Jack Mackerel Meal on Growth, Feed Availability, and Biochemical Composition

Application of feed stimulants is very helpful to increase the feed intake of fish, especially in the development of low fish meal (FM) diets. FM replacement effect by various plant protein sources (corn gluten meal (CGM), soy protein concentrate (SPC), and corn protein concentrate (CPC)) in diets with an addition of jack mackerel meal (JMM) as feed stimulants on growth, feed availability, and biochemical composition of olive flounder was elucidated. An experimental design of two-way (two replacement levels (25% and 50%) × 3 replacement sources (CGM, SPC, and CPC)) analysis of variance was adopted. Seven diets were formulated. Amount of 60% FM was contained in the control (Con) diet. In the Con diet, 25% and 50% FM were replaced by CGM, SPC, and CPC with an addition of 12% JMM as feed stimulants, referred to as the CGM25, CGM50, SPC25, SPC50, CPC25, and CPC50 diets, respectively. Four hundred and twenty juvenile fish were distributed into 21 flow-through tanks. All diets were assigned to triplicate groups of fish. Fish were hand-fed to satiation twice a day for 56 days. Both dietary replacement levels and sources had statistical effect on weight gain (P < 0.0001 and P < 0.045, respectively), specific growth rate (SGR) (P < 0.0001 and P < 0.033), and feed consumption (P < 0.0001 and P < 0.03) of fish. Dietary increased FM replacement levels lowered weight gain, SGR, and feed consumption of fish. Weight gain, SGR, and feed consumption of fish fed the Con and CGM25 diets were statistically (P < 0.05) greater than those of fish fed the CGM50, SPC50, and CPC50 diets. Both replacement level and source had no statistical effect on feed utilization, biochemical composition except for statistical effect of replacement source on glycine content of fish, and lysozyme and superoxide dismutase (SOD) activities of fish. FM up to 25% could be substituted with CGM, SPC, and CPC in the olive flounder feeds supplemented with 12% JMM as feed stimulants without compromising growth, feed utilization, and lysozyme and SOD activities.

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.

Efficacy of Single and Multi-Strain Probiotics on In Vitro Strain Compatibility, Pathogen Inhibition, Biofilm Formation Capability, and Stress Tolerance

Compatibility of each strain in a multi-strain probiotic (MSP), along with its properties, becomes a strong base for its formulation. In this study, single-strain probiotics (SSPs) and multi-strain probiotics (MSPs) were evaluated in vitro for strain compatibility, microbial antagonism, biofilm formation capacity, and stress tolerance. Bacillus amyloliquefaciens L11, Enterococcus hirae LAB3, and Lysinibacillus fusiformis SPS11 were chosen as MSP1 candidates because they showed much stronger antagonism to Aeromonas hydrophila and Streptococcus agalactiae than a single probiotic. MSP 2 candidates were Lysinibacillus fusiformis strains SPS11, A1, and Lysinibacillus sphaericus strain NAS32 because the inhibition zone produced by MSP 2 against Vibrio harveyi and Vibrio parahaemolyticus was much higher than that produced by its constituent SSPs. MSP1 in the co-culture assay reduced (p < 0.05) A. hydrophila count from 9.89 ± 0.1 CFU mL−1 to 2.14 ± 0.2 CFU mL−1. The biofilm formation of both MSPs were significantly higher (p < 0.05) than its constituent SSPs and the pathogens. The SSPs in both MSPs generally showed resistance to high temperatures (80, 90, and 100 °C) and a wide range of pH (2 to 9). This in vitro assessment study demonstrates that MSP1 and 2 have the potential to be further explored as multi-strain probiotics on selected aquatic species.

The synergetic effect of Bacillus species and Yucca shidigera extract on water quality, histopathology, antioxidant, and innate immunity in response to acute ammonia exposure in Nile tilapia

Acute ammonia toxicity suppresses the immune function and enhances the inflammatory pathways in Nile tilapia. The aim of this study was to compare the effect of Bacillus strains probiotic mixture (BS) or Yucca shidigera liquid extract (YSE) alone or their combination in water treatment and in reliving toxicity of an acute ammonia exposure in Nile tilapia through the assessment of fish immune response, inflammatory pathway, oxidative stress response with respect to the histopathological changes, gene expression, enzymes levels and phagocytosis. Five groups were used; the 1st and 2nd groups fed the basal diet; the 3rd group fed basal diet with BS in water, 4th group fed basal diet and supplemented with YSE in water and 5th group received a combination of BS and YSE. After two weeks of treatments, the 2nd, 3rd, 4th, and the 5th groups were exposed to acute ammonia challenge for 72 h. Fish exposed to ammonia displayed significant decreases in RBCs, Hb, PCV, WBCs, phagocytic activity (PA) and index (PI), lysozyme activities and serum antioxidant enzymes (glutathione peroxidase (GPX) and catalase (CAT)). Also, a significant increase in Malondialdehyde (MDA), degenerative changes in the gills, hepatopancrease and spleen associated with an elevated un-ionized ammonia level. A significant restoration of the hematological parameters was observed with the use of BS, YSE or their combination. Additionally, they improved the innate immunity, antioxidant responses, and histopathological changes. At transcriptomic level, ammonia toxicity significantly lowered the mRNA transcription levels of Nuclear erythroid 2-related factor 2 (Nrf2), quinone oxidoreductase 1 (NQO-1), Heme oxygenase 1 (HO-1) and Heat shock proteins (HSP70). While nuclear factor kappa β (NFкβ), Tumor necrosis factor α (TNF-α), Interleukin 1β (IL-1β), and Interleukin 8 (IL8), transcription levels were increased. Interestingly, BS and YSE and their combination significantly increased the expression of these genes with the highest levels reported with BS and YSE combination. We observed that, the most pronounced restoration of some important inflammatory and immune related genes close to the control level was observed when BS-YSE mix was used. Furthermore, a restored water pH, and a maintained ammonia level to the control level were observed in this group. Otherwise, equal effects for the three treatments were observed on the assessed parameters. We recommend the used of BS-YSE mix for water ammonia treatment and relieving ammonia toxicity in fish.

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.

Different response of Acipenser gueldenstaedtii CRP/SAP and SAA to bacterial challenge and chronic thermal stress sheds light on the innate immune system of sturgeons

Sturgeons are chondrostean fish critically endangered due to anthropogenic loss and degradation of natural habitat and overfishing for meat and caviar production. Consequently, sturgeon aquaculture has extensively developed lately, being Russian sturgeon (Acipenser gueldenstaedtii) the second most important species reared for caviar production. However, Russian sturgeon aquaculture in subtropical countries, such as Uruguay, confronts difficulties because fish have to endure excessive summertime warm temperatures, which weaken their innate defences facilitating opportunistic infections. To address this problem, we look for identifying putative acute phase proteins (APPs), which might be robust serum biomarkers of both infection and chronic thermal stress, applied to monitoring Russian sturgeon health status in farms. We focused on the C-Reactive Protein/Serum Amyloid P (CRP/SAP) pentraxin since the pentraxin family includes well-known APPs, better characterised in mammals than fish. We identified A.gueldenstaedtii CRP/SAP (AgCRP/SAP), as a member of the universal CRP/SAP pentraxin sub-family, and studied AgCRP/SAP involvement in sturgeon response to bacterial challenge and chronic thermal stress, in comparison with A. gueldenstaedtii Serum Amyloid A (AgSAA), a previously described positive APP. Results showed that AgCRP/SAP is a constitutive serum component that remained constant upon Aeromonas hydrophila challenge and chronic thermal stress. Contrastingly, serum AgSAA was subjected to regulation by bacterial and thermal stress challenges, showing a 50-fold increase and 3-fold decline in serum levels, respectively. Overall, results highlight the potential value of AgSAA, but not of AgCRP/SAP, as a biomarker of bacterial infection and the need to continue searching for robust chronic thermal stress biomarkers in sturgeons.

Mechanisms and the role of probiotic Bacillus in mitigating fish pathogens in aquaculture

Diseases are natural components of the environment, and many have economic implications for aquaculture and fisheries. Aquaculture is a fast-growing industry with the aim to meet the high protein demand of the ever-increasing global population; however, the emergence of diseases is a major setback to the industry. Probiotics emerged as a better solution to curb the disease problem in aquaculture among many alternatives. Probiotic Bacillus has been proven to better combat a wide range of fish pathogens relative to other probiotics in aquaculture; therefore, understanding the various mechanisms used by Bacillus in combating diseases will help improve their mode of action hence yielding better results in their combat against pathogens in the aquaculture industry. Thus, an overview of the mechanisms (production of bacteriocins, suppression of virulence gene expression, competition for adhesion sites, production of lytic enzymes, production of antibiotics, immunostimulation, competition for nutrients and energy, and production of organic acids) used by Bacillus probiotics in mitigating fish pathogens ranging from Aeromonas, Vibrio, Streptococcus, Yersinia, Pseudomonas, Clostridium, Acinetobacter, Edwardsiella, Flavobacterium, white spot syndrome virus, and infectious hypodermal and hematopoietic necrosis virus proven to be mitigated by Bacillus have been provided.

Genome-Wide Identification of hsp90 Gene in Rainbow Trout (Oncorhynchus mykiss) and Their Regulated Expression in Response to Heat Stress

In this study, we analyzed the gene structure, chemical characterizations, chromosome locations, evolutionary relationship, and expression profile of hsp90 genes with online database. In addition, the expression levels of hsp90s were also investigated under heat stress by quantitative real-time (qRT)-PCR. A total of eight hsp90 genes were identified from the rainbow trout genome. They were all distributed on chromosomes 2, 4, 8, and 13. The molecular weight ranged from 78.93 to 91.39 kDa, and the isoelectric point ranged from 4.84 to 4.96. The eight hsp90 genes were clustered into six subfamilies (A, B, C, D, E, and F). Genetic structure and conserved domain analysis revealed that all eight hsp90 genes had only one exon, and motif 1-motif 10 was shared by most genes. According to RNA-seq analysis of rainbow trout liver and head kidney, a total of seven out of eight genes were significantly upregulated under heat stress, and qRT-PCR was carried out on these seven genes; the expression levels of these genes were significantly upregulated under heat stress. The significantly regulated expressions of hsp90 genes under heat stress indicated that hsp90 genes are involved in heat stress response in rainbow trout. This study provides a theoretical basis for further study on the role of hsp90 in the heat stress tolerance of rainbow trout.

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.

A review on the application of Bacillus as probiotics in aquaculture

Probiotics use in aquaculture has gained attention as microbial candidates to maintain the health and the well-being of many aquaculture animals. Among the many microbial candidates, probiotic Bacillus has sporulation capacity that makes them survive harsh environmental conditions, are non-pathogenic and non-toxic when fed to fish, and can produce antimicrobial substances making them more suitable candidates compared to other probiotics. In this review, we discussed the necessity of using the probiotic Bacillus in sustainable aquaculture as a good alternative to improve feed utilization, stress response, immune response and disease resistance, maintenance of tissue integrity, and as well improvement of water quality for sustainable aquaculture. Therefore the findings of current researches about the effects of Bacillus application to improve the culture of aquatic animals for future research and development of Bacillus application in aquaculture have been summarised.

Effects of Temperature on the Expression of Two Ovarian Differentiation-Related Genes foxl2 and cyp19a1a

Exposure to stress induces a series of responses and influences a wide range of biological processes including sex differentiation in fish. The present work investigated the molecular and physiological response to thermal stress throughout the early development stage covering the whole period of sex differentiation of bluegill, Lepomis macrochirus. Larvae were treated using three temperatures, 17, 24, and 32°C from 6 to 90 days posthatching (dph) in 30-L round tanks. There is no significant difference of the sex ratio and survival among the three temperature groups in the geographic population used in this study. Two ovarian differentiation-related genes foxl2 and cyp19a1a were detected at 7 dph suggesting that these genes have already played a role prior to sex differentiation. The expression of foxl2 reached the peak and was thermosensitive just prior to the onset of ovarian differentiation at 27 dph. Histological examination displayed that the proliferation of germ cells and ovarian differentiation were delayed at the low-temperature treatment (17°C) at 97 dph compared with higher temperatures. In conclusion, the water temperature regulates the sex differentiation of bluegill through modulation of the expression of foxl2 and cyp19a1a. A comparative study of the expression profile of sex differentiation-related genes in species will shed light on the evolution of sex-determination mechanisms and the impact of stress on sex differentiation.