Lactobacillus rhamnosus GG triggers intestinal epithelium injury in zebrafish revealing host dependent beneficial effects

Activation of Gut Microbiota-HIF1α Axis Effectively Restores Resistance to Aeromonas veronii Caused by Improper Administration of AiiO-AIO6

BACKGROUND

Feeding adult zebrafish a diet supplemented with quenching enzyme AiiO-AIO6 (AIO6) for 3 wk improved the growth performance and disease resistance. However, when the feeding period was extended to 8 wk, zebrafish's disease resistance to Aeromonas veronii decreased.

OBJECTIVES

We investigated the mechanisms of the reduced disease resistance of zebrafish induced by feeding on an AIO6 supplemented diet for a long term (8 wk) and assessed the effectiveness of feed additives in restoring the low disease resistance.

METHODS

One-month-old (adult) zebrafish were fed with a basal diet and the basal diet supplemented with AIO6 (10 U/g) for 8 wk (experiment 1). Furthermore, the zebrafish larvae model (experiment 2) was developed and used to study the mechanisms of how AIO6 affected disease resistance (experiment 3). We also investigated the effectiveness of selected prebiotic tributyrin, β-glucan or mannan in activating gut microbiota- HIF1α to restore the low disease resistance of adult zebrafish fed with AIO6 for 8 wk (experiment 4). Lastly, the effects of Bacillus subtilis in activating the gut microbiota-HIF1α and improving the low disease resistance of zebrafish larvae induced by AIO6 were examined (experiment 5).

RESULTS

Feeding adult zebrafish with AIO6 for 8 wk promoted growth but disordered the gut microbiota and reduced disease resistance. The zebrafish larvae model confirmed that feeding AIO6 for 2 d increased disease resistance, whereas 7 d decreased the resistance by suppressing HIF1α. Using a germ-free zebrafish larvae model, we also demonstrated that AIO6-induced gut microbiota mediated inhibition of HIF1α. Furthermore, zebrafish fed on the AIO6-containing diet supplement with tributyrin, β-glucan, mannan, or Bacillus subtilis activated the gut microbiota-HIF1α axis to reverse the low resistance caused by AIO6.

CONCLUSIONS

Activating the gut microbiota-HIF1α axis has a vital role in improving intestinal health and restores the low resistance to Aeromonas veronii caused by improper administration of dietary AIO6 in zebrafish.

New Insights into Melatonin's Function on Thiacloprid-Induced Pyroptosis and Inflammatory Response in Head Kidney Lymphocytes of Cyprinus carpio: Implicating Mitochondrial Metabolic Imbalance and mtROS/cGAS-STING/NF-κB Axis

Thiacloprid (THI) is a synthetic insecticide, the misuse is targeted chiefly to control aphid pest species in orchards and vegetables. Melatonin (MET) is a hormone that plays crucial physiological roles in anti-inflammatory capacities of fish. We explored the function of MET (100 μM) to mitigate the toxicity induced by THI (20 μM) in lymphocytes. Our results indicate that THI led to a notable rise in lymphocyte mortality. Lymphocytes exposed to THI exhibited a heightened incidence of pyroptosis, accompanied by upregulation in expression associated with pyroptosis (NLRP3, GSDMEA, and IL-18). Meanwhile, THI exposure led to a decrease in lymphocyte mitochondrial membrane potential, an increase in mtROS levels, and a reduction in intracellular ATP, DNA, and NADPH/NADP+ levels, indicating an imbalance in the mitochondrial metabolism within the lymphocytes. Additionally, these effects were reversed by MET treatment, where MitoQ treatment showed that the suppression of mtROS reduced the lymphocyte pyroptosis caused by THI via the mtROS/cGAS-STING/NF-κB axis. Importantly, MET provided defense against the immunotoxic impacts of THI by ameliorating pyroptosis and enhancing anti-inflammatory capability via the mtROS/cGAS-STING/NF-κB axis. Our research potentiates the safeguarding of cultured fish from biological hazards caused by THI and highlights the valuable application of MET in common carp.

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

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

The intestinal microbiome and Cetobacterium somerae inhibit viral infection through TLR2-type I IFN signaling axis in zebrafish

BACKGROUND

Evidence has accumulated to demonstrate that intestinal microbiome can inhibit viral infection. However, our knowledge of the signaling pathways and identity of specific commensal microbes that mediate the antiviral response is limited. Zebrafish have emerged as a powerful animal model for study of vertebrate-microbiota interactions. Here, a rhabdoviral infection model in zebrafish allows us to investigate the modes of action of microbiome-mediated antiviral effect.

RESULTS

We observed that oral antibiotics-treated and germ-free zebrafish exhibited greater spring viremia of carp virus (SVCV) infection. Mechanistically, depletion of the intestinal microbiome alters TLR2-Myd88 signaling and blunts neutrophil response and type I interferon (IFN) antiviral innate immunity. Through 16S rRNA sequencing of the intestinal contents from control and antibiotic(s)-treated fish, we identified a single commensal bacterial species, Cetobacterium somerae, that can restore the TLR2- and neutrophil-dependent type I IFN response to restrict SVCV infection in gnotobiotic zebrafish. Furthermore, we found that C. somerae exopolysaccharides (CsEPS) was the effector molecule that engaged TLR2 to mediate the type I IFN-dependent antiviral function.

CONCLUSIONS

Together, our results suggest a conserved role of intestinal microbiome in regulating type I IFN antiviral response among vertebrates and reveal that the intestinal microbiome inhibits viral infection through a CsEPS-TLR2-type I IFN signaling axis in zebrafish. Video Abstract.

Fish gut-derived probiotic Pediococcus pentosaceus alleviates gossypol-induced intestinal inflammation by inhibiting NLRC3/NF-κB/IL-1β signal pathway in Nile tilapia

Cottonseed meal (CSM) and cottonseed protein concentrate (CPC) serve as protein alternatives to fish meal and soybean meal in the feed industry. However, the presence of gossypol residue in CSM and CPC can potentially trigger severe intestinal inflammation, thereby restricting the widespread utilization of these two protein sources. Probiotics are widely used to prevent or alleviate intestinal inflammation, but their efficacy in protecting fish against gossypol-induced enteritis remains uncertain. Here, the protective effect of Pediococcus pentosaceus, a strain isolated from the gut of Nile tilapia (Oreochromis niloticus), was evaluated. Three diets, control diet (CON), gossypol diet (GOS) and GOS supplemented with P. pentosaceus YC diet (GP), were used to feed Nile tilapia for 10 weeks. After the feeding trial, P. pentosaceus YC reduced the activity of myeloperoxidase (MPO) in the proximal intestine (PI) and distal intestine (DI). Following a 7-day exposure to Aeromonas hydrophila, the addition of P. pentosaceus YC was found to increase the survival rate of the fish. P. pentosaceus YC significantly inhibited the oxidative stress caused by gossypol, which was evidenced by lower reactive oxygen species (ROS) and malondialdehyde (MDA), as well as higher activities of glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) in PI and DI. Addition of P. pentosaceus YC significantly inhibited enteritis, with the lower expression of pro-inflammatory cytokines (il-1β, il-6, il-8) and higher expression of anti-inflammatory cytokines tgf-β. RNA-seq analysis indicated that P. pentosaceus YC supplementation significantly inhibited nlrc3 and promoted nf-κb expression in PI and DI, and the siRNA interference experiment in vivo demonstrated that intestinal inflammation was mediated by NLRC3/NF-κB/IL-1β signaling pathway. Fecal bacteria transplantation experiment demonstrated that gut microbiota mediated the protective effect of P. pentosaceus YC. These findings offer valuable insights into the application of P. pentosaceus YC for alleviating gossypol-induced intestinal inflammation in fish.

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.