Exposure of lead on intestinal structural integrity and the diversity of gut microbiota of common carp

Metagenomic insights into the alterations of gut microbial community in Bufo gargarizans tadpoles following lead exposure

Lead (Pb), a prevalent heavy metal contaminant in aquatic environments, has complex effects on the gut microbiome function of aquatic animals. In this study, metagenomic analysis of Bufo gargarizans tadpoles was carried out following Pb exposure. Moreover, histological analysis was performed on the intestines. The results showed that Pb exposure induced histological damage to the intestinal epithelium. Significant differences in microbial abundance and function were detected in the 200 μg/L Pb group compared to the control group. Specifically, an increase in Bosea and Klebsiella was noted at 200 μg/L Pb, which potentially could induce inflammation in tadpoles. Notably, the decrease in the abundance of glycoside hydrolases subsequent to exposure to 200 μg/L Pb is likely to attenuate carbohydrate metabolism. Furthermore, increased fluoroquinolone-related antibiotic resistance genes (ARGs), phenolic-related ARGs, and iron uptake systems following 200 μg/L Pb exposure might heighten the disease risk for tadpoles. These discoveries augment our comprehension of the influences of Pb on the intestinal well-being of amphibians and offer valuable insights for further assessment of the ecological risks that Pb poses to amphibians.

Systemic toxicity of biodegradable polyglycolic acid microplastics on the gut-liver-brain axis in zebrafish

Polyglycolic acid (PGA), a novel type of hazardous biodegradable plastic, is gradually being widely used in the biomedical and food packaging industries. However, the long-term ecological effects of PGA degradation to microplastics (MPs) in aquatic organisms remain unknown. The gut-liver-brain axis regulates the exchange of information between the gut, liver, and brain, and is a key target for tissue damage caused by pollutants. Adult zebrafish were exposed to 1 or 100 mg/L PGA MP suspension for 28 d. PGA affects the intestinal vascular barrier through gene expression downstream of the Wnt/β-catenin pathway, increasing intestinal permeability and disrupting the environment of intestinal microbial diversity. This, in turn, promoted the accumulation of lipopolysaccharide (LPS). Disturbance of the intestinal microbiota balance and its metabolites are transferred to the liver and brain through the gut-liver-brain axis, causing disorders in hepatic lipid metabolism and synthesis. Behavioural experiments showed that long-term exposure to PGA MP caused anxiety-like behaviour and cognitive impairment, which may be related to the disruption of the gut-liver-brain axis, thus inducing inflammation and disrupting the normal functioning of the body. In summary, this study evaluated the safety of the new degradable plastic, PGA, but its ecological risks still require attention.

Intestinal toxicity of Pb: Structural and functional damages, effects on distal organs and preventive strategies

Lead (Pb) is one of the most common heavy metal pollutants that possesses multi-organ toxicity. For decades, great efforts have been devoted to investigate the damage of Pb to kidney, liver, bone, blood cells and the central nervous system (CNS). For the common, dietary exposure is the main avenue of Pb, but our knowledge of Pb toxicity in gastrointestinal tract (GIT) remains quite insufficient. Importantly, emerging evidence has documented that gastrointestinal disorders affect other distal organs like brain and liver though gut-brain axis or gut-liver axis, respectively. This review focuses on the recent understanding of intestinal toxicity of Pb exposure, including structural and functional damages. We also review the influence and mechanism of intestinal toxicity on other distal organs, mainly concentrated on brain and liver. At last, we summarize the bioactive substances that reported to alleviate Pb toxicity, providing potential dietary intervention strategies to prevent or attenuate Pb toxicity.

Niclosamide subacute exposure alters the immune response and microbiota of the gill and gut in black carp larvae, Mylopharyngodon piceus

Niclosamide (NIC) is a commonly used insecticide and molluscicide in the prevention and treatment of parasitic diseases in fish. The utilization of NIC has the potential to disrupt the microbial community present on the mucosal tissue of fish, leading to localized inflammatory responses. The objective of this study was to evaluate the impact of NIC on the immune system and bacterial populations within the gill and gut of Mylopharyngodon piceus. Fish were subjected to varying concentrations of NIC, including a control group (0 μg/L), a low NIC group (15% 96 h LC50, LNG, 9.8 μg/L), and a high NIC group (80% 96 h LC50, HNG, 52.5 μg/L). Gill and gut samples were collected 28 days post-exposure for analysis. The findings revealed that the 96-h LC50 for NIC was determined to be 65.7 μg/L, and histopathological examination demonstrated that exposure to NIC resulted in gill filament subepithelial edema, exfoliation, degeneration, and a decrease in gill filament length. Furthermore, the gut exhibited apical enterocyte degeneration and leucocyte infiltration following NIC exposure. Additionally, NIC exposure led to a significant elevation in the levels of immunoglobulin M (IgM), complement component 3 (C3), and complement component 4 (C4) in both gill and gut tissues. Moreover, the activity of lysozyme (LYZ) was enhanced in the gill, while the activities of peroxidase (POD) and immunoglobulin T (IgT) were increased in gut tissue. The exposure to NIC resulted in enhanced mRNA expression of c3, c9, tnfα, il6, il8, and il11 in the gill tissue, while decreasing c3 and il8 expression in the gut tissue. Furthermore, the natural resistance-associated macrophage protein (nramp) mRNA increased, and liver-expressed antimicrobial peptide 2 (leap2) mRNA decreased in gill and gut tissues. And hepcidin (hepc) mRNA levels rose in gill but fell in gut tissue. NIC exposure also led to a decrease in gill bacterial richness and diversity, which significantly differed from the control group, although this separation was not significant in the gut tissue. In conclusion, the administration of NIC resulted in alterations in both the immune response and mucosal microbiota of fish. Furthermore, it was noted that gills displayed a heightened vulnerability to sublethal effects of NIC in comparison to gut tissues.

Alpha-glycosyl isoquercitrin alleviates subchronic social defeat stress-induced depression symptoms by modulating the microbiota-gut-brain axis in mice

AIMS

Increasing evidence suggests a link between gut microbial dysbiosis and the pathogenesis of depression. Alpha-glycosyl isoquercitrin (AGIQ), consisting of isoquercitrin and its glycosylated quercetin, has beneficial effects on the gut microbiome and brain function. Here, we detected the potential antidepressant impact of a four-week administration of AGIQ and its underlying mechanisms using a mouse model of depression.

MAIN METHODS

Male C57BL/6 mice were orally administered AGIQ (0.05 % or 0.5 % in drinking water) for 28 days; subchronic social defeat stress was performed in the last 10 days. Behavior tests were conducted to assess anxiety and depressive-like behaviors. Additionally, evaluations encompassed 5-hydroxytryptamine (5-HT) levels, the gut microbiota composition, lipopolysaccharide (LPS) concentrations, short-chain fatty acids levels, and intestinal barrier integrity changes.

KEY FINDINGS

AGIQ significantly alleviated depression-like behaviors and increased hippocampal 5-HT levels. Further, AGIQ mitigated stress-induced gut microbial abnormalities and reduced the levels of LPS in the serum, which affected the relative gene expression levels of 5-HT biosynthesis enzymes in vitro. Furthermore, AGIQ reversed the reduced butyrate levels in cecal contents and improved the impaired intestinal barrier by increasing the expression of colonic zonula occluden-1 (ZO-1) and occludin, thereby decreasing LPS leakage.

SIGNIFICANCE

Our results suggest that AGIQ could improve stress-induced depression by regulating the gut microbiome, which inhibits LPS production and maintains the gut barrier. This is the first report on the potential effect of AGIQ on depression via the gut microbiota-brain axis, shedding new light on treatment options.

Lead exposure disrupted ileal barrier of developmental Japanese quails(Coturnix japonica): Histopathological damages, microbiota dysbiosis and immune disorder

The gut barrier plays an essential role in maintaining homeostasis and is usually composed of a mechanical barrier, a chemical barrier, an immune barrier, and a biological barrier. However, the impacts of lead (Pb) exposure on avian gut barrier are still unclear. Therefore, the present study tried to determine the toxic effects of Pb on ileal barrier of a biological model-Japanese quail (Coturnix japonica). One-week old quails were exposed to 0, 50, 500 and 1000 ppm Pb in drinking water for 5 weeks. The results showed mechanic barrier in the ileum was disrupted with microstructural deformation featured by epithelial cell abscission, villi contractions and goblet cells reduction as well as ultrastructural changes characterized by swollen mitochondria, blurry tight junctions and microvilli subtraction. Meanwhile, the expression of genes associated with intestinal tight junctions was downregulated in Pb-treated groups indicating tight junction malfunction. Moreover, less mucus and downregulation of expression of mucin2 (Muc2) and Krüppel-like factor 4 (Klf4) indicated chemical barrier disturbance by Pb. In addition, the alteration of microbial diversity and emergence of pathogen bacteria suggested ileal biological barrier disruption by Pb. Furthermore, Pb caused immune dysfunction in the ileum through promoting the expression of pro-inflammatory factors including interleukin 1 beta (IL-1β), interleukin 6 (IL-6), Interferon gamma (IFN-γ), tumor necrosis factor alpha (TNF-α) and nuclear factor kappa B (NF-κB) and inhibiting the expression of anti-inflammatory factor interleukin 10 (IL-10). The present study demonstrated that Pb may pose health risks to birds through gut barrier damages.

Conventional Anthelmintic Concentration of Deltamethrin Immersion Disorder in the Gill Immune Responses of Crucian Carp

Current treatment strategies for parasitic infectious diseases in crucian carp primarily rely on chemotherapy. As a commonly used antiparasitic agent, deltamethrin (DEL) may have the potential adverse effects on external mucosa of fish such as gills. In this study, 180 healthy juvenile crucian carp (Carassius auratus) (average weight: 8.8 ± 1.0 g) were randomly divided into three groups for 28 days, which were immersed in 0 μg/L, 0.3 μg/L, and 0.6 μg/L of DEL, respectively. The results of histological analysis revealed that severe hyperplasia in the secondary lamellae of gills was observed, and the number of goblet (mucus-secreting) cells increased significantly after DEL immersion. TUNEL staining indicated that the number of apoptotic cells increased in crucian carp gill. At the molecular level, the mRNA expression analysis revealed significant upregulation of apoptosis (caspase 3, caspase 8, and bax), autophagy (atg5 and beclin-1), and immune response (lzm, muc5, il-6, il-8, il-10, tnfα, ifnγ, tgfβ, tlr4, myd88, and nf-kb), whereas tight junction-related genes (occludin and claudin12) were downregulated after DEL immersion, suggesting that DEL immersion altered innate immunity responses and promoted mucus secretion. Moreover, tandem mass tag (TMT)-based proteomics revealed that a total of 428 differentially expressed proteins (DEPs) contained 341 upregulated DEPs and 87 downregulated DEPs with function annotation were identified between the control and DEL groups. Functional analyses revealed that the DEPs were enriched in apoptotic process, phagosome, and lysosome pathways. Additionally, DEL immersion also drove gill microbiota to dysbiosis and an increase in potentially harmful bacteria such as Flavobacterium. Overall, this study showed that DEL elicited shifts in the immune response and changes in the surface microbiota of fish. These results provide new perspectives on the conventional anthelmintic concentration of DEL immersion disorder of the gill immune microenvironment in crucian carp and theoretical support for future optimization of their practical application.

Angelica sinensis aboveground part polysaccharide and its metabolite 5-MT ameliorate colitis via modulating gut microbiota and TLR4/MyD88/NF-κB pathway

The roots of Angelica sinensis have been used in Traditional Chinese Medicine for thousands of years. However, tons of aerial parts of this herb (aboveground part) are commonly discarded during the process of root preparations. A polysaccharide (ASP-Ag-AP) in the aboveground parts of A. sinensis was isolated and preliminarily characterized as typical plant pectin. ASP-Ag-AP exhibited noticeable protective effects against dextran sodium sulfate (DSS)-induced colitis, including reduction of colonic inflammation, modulation of barrier function, and alteration of gut microbiota and serum metabolite profile. Anti-inflammatory effects of ASP-Ag-AP were observed by inhibiting TLR4/MyD88/NF-κB signaling pathway in vitro and in vivo. Additionally, the level of serum metabolite 5-methyl-dl-tryptophan (5-MT) was reduced by DSS and restored by ASP-Ag-AP, which also negatively correlated with Bacteroides, Alistipes, Staphylococcus and pro-inflammatory factors. The protection from inflammatory stress on intestinal porcine enterocytes cells (IPEC-J2) of 5-MT was observed through the inhibition of TLR4/MyD88/NF-κB pathway. Besides, 5-MT also exhibited robust anti-inflammatory effect in colitis mice with improving colitis symptoms, barrier function and gut microbiota, which was the same as presented by ASP-Ag-AP. Therefore, ASP-Ag-AP could be a promising agent for colitis prevention and 5-MT could be the signal metabolite of ASP-Ag-AP on defending against intestinal inflammatory stress.

Effects of microplastics and lead exposure on gut oxidative stress and intestinal inflammation in common carp (Cyprinus carpio L.)

Microplastics (MPs) are increasingly being detected in freshwater environments, which have the potential to cause combined toxicity with other contaminants on aquatic organisms. To reveal the ecological risks, the combined effects of lead (Pb) and polyvinyl chloride microplastics (MPs) were explored in the gut of common carp (Cyprinus carpio L.). The results confirmed that exposure of Pb alone accelerated Pb accumulation, increased oxidative stress, and activated the inflammation response of the gut. However, the aforementioned effects all decreased under the co-exposure of Pb and MPs. In addition, MPs altered intestinal microbial community of common carp, especially the abundance of immune system-related species. All measured variables were organized for partial least square path modeling, which revealed the combined effects of Pb and MPs on inflammation response. The results implied that MPs reduced inflammation response in two ways, including the reduction of intestinal Pb accumulation and the alteration of the intestinal microbial community. Overall, this study provides a novel aspect of ecological effects on aquatic animals from Pb and MPs exposure. The interesting results remind us that when exploring the ecological risks of MPs, combined effects from other toxic substances must be considered simultaneously.

Metagenomics analysis reveals the effects of norfloxacin on the gut microbiota of juvenile common carp (Cyprinus carpio)

Norfloxacin (NOR) is an early third-generation quinolone antibiotic that has been widely used in animal husbandry and aquaculture because of its bactericidal properties. As an emerging contaminant, NOR may have toxic effects on fish. This study assessed the chronic toxicity (6 weeks) of 0 (control group), 100 ng/L (environmental concentration), and 1 mg/L NOR to the gut microbiota of juvenile common carp (Cyprinus carpio) based on metagenomic sequencing. Metagenomic analysis revealed that the Proteobacteria, Bacteroidetes, Fusobacteria, Firmicutes, and Actinobacteria were the dominant bacteria in the gut of common carp. The relative abundance of Actinobacteria was highest in the control group. The alpha diversity of the environmental concentration NOR was significantly lower than the control group. Principal coordinates analysis (PCoA) indicated that the bacterial community between the different groups formed clear separate clusters. NOR exposure adversely could affect immune function and some substance metabolic pathways in the gut microbiota of common carp. Furthermore, environmental concentrations of NOR produce antibiotic resistance genes (ARGs) in the gut microbiota, enhancing resistance to drugs. In conclusion, environmental concentrations of NOR could alter the composition, structure, and abundance of ARGs in the gut microbiota, thereby affecting the intestinal health of fish.

Heavy metals (HMs) pollution in the aquatic environment: Role of probiotics and gut microbiota in HMs remediation

The presence of heavy metals (HMs) in aquatic ecosystems is a universal concern due to their tendency to accumulate in aquatic organisms. HMs accumulation has been found to cause toxic effects in aquatic organisms. The common HMs-induced toxicities are growth inhibition, reduced survival, oxidative stress, tissue damage, respiratory problems, and gut microbial dysbiosis. The application of dietary probiotics has been evolving as a potential approach to bind and remove HMs from the gut, which is called "Gut remediation". The toxic effects of HMs in fish, mice, and humans with the potential of probiotics in removing HMs have been discussed previously. However, the toxic effects of HMs and protective strategies of probiotics on the organisms of each trophic level have not been comprehensively reviewed yet. Thus, this review summarizes the toxic effects caused by HMs in the organisms (at each trophic level) of the aquatic food chain, with a special reference to gut microbiota. The potential of bacterial probiotics in toxicity alleviation and their protective strategies to prevent toxicities caused by HMs in them are also explained. The dietary probiotics are capable of removing HMs (50-90%) primarily from the gut of the organisms. Specifically, probiotics have been reported to reduce the absorption of HMs in the intestinal tract via the enhancement of intestinal HM sequestration, detoxification of HMs, changing the expression of metal transporter proteins, and maintaining the gut barrier function. The probiotic is recommended as a novel strategy to minimize aquaculture HMs toxicity and safe human health.

Intestinal response of Rana chensinensis larvae exposed to Cr and Pb, alone and in combination

Although numerous investigations on the adverse impact of Cr and Pb have been performed, studies on intestinal homeostasis in amphibians are limited. Here, single and combined effects of Cr (104 μg/L) and Pb (50 μg/L) on morphological and histological features, bacterial community, digestive enzymes activities, as well as transcriptomic profile of intestines in Rana chensinensis tadpoles were assessed. Significant decrease in the relative intestine length (intestine length/snout-to-vent length, IL/SVL) was observed after exposure to Pb and Cr/Pb mixture. Intestinal histology and digestive enzymes activities were altered in metal treatment groups. In addition, treatment groups showed significantly increased bacterial richness and diversity. Tadpoles in treatment groups were observed to have differential gut bacterial composition from controls, especially for the abundance of phylum Proteobacteria, Firmicutes, Verrucomicrobia, Actinobacteria, and Fusobacteria as well as genus Citrobacter, Anaerotruncus, Akkermansia, and Alpinimonas. Moreover, transcriptomic analysis showed that the transcript expression profiles of GPx and SOD isoforms responded differently to Cr and/or Pb exposure. Besides, transcriptional activation of pro-apoptotic and glycolysis-related genes, such as Bax, Apaf 1, Caspase 3, PK, PGK, TPI, and GPI were detected in all treatment groups but downregulation of Bcl2 in Pb and Cr/Pb mixture groups. Collectively, these results suggested that Cr and Pb exposure at environmental relevant concentration, alone and in combination, could disrupt intestinal homeostasis of R. chensinensis tadpoles.

Copper-mediated shifts in transcriptomic responses of intestines in Bufo gargarizans tadpoles to lead stress

The differential transcriptomic responses of intestines in Bufo gargarizans tadpoles to Pb alone or in the presence of Cu were evaluated. Tadpoles were exposed to 30 μg/L Pb individually and in combination with Cu at 16 or 64 μg/L from Gosner stage (Gs) 26 to Gs 38. After de novo assembly, 105,107 unigenes were generated. Compared to the control group, 7387, 6937, and 11139 differentially expressed genes (DEGs) were identified in the treatment of Pb + Cu0, Pb + Cu16, and Pb + Cu64, respectively. In addition, functional annotation and enrichment analysis of DEGs revealed substantial transcriptional reprogramming of diverse molecular and biological pathways were induced in all heavy metal treatments. The relative expression levels of genes associated with intestinal epithelial barrier and bile acids (BAs) metabolism, such as mucin2, claudin5, ZO-1, Asbt, and Ost-β, were validated by qPCR. This study demonstrated that Pb exposure induced transcriptional responses in tadpoles, and the responses could be modulated by Cu.

Towards the Sustainable Exploitation of Salt-Tolerant Plants: Nutritional Characterisation, Phenolics Composition, and Potential Contaminants Analysis of Salicornia ramosissima and Sarcocornia perennis alpini

Increasing soil salinisation represents a serious threat to food security, and therefore the exploitation of high-yielding halophytes, such as Salicornia and Sarcocornia, needs to be considered not merely in arid regions but worldwide. In this study, Salicornia ramosissima and Sarcocornia perennis alpini were evaluated for nutrients, bioactive compounds, antioxidant capacity, and contaminants. Both were shown to be nutritionally relevant, exhibiting notable levels of crude fibre and ash, i.e., 11.26-15.34 and 39.46-40.41% dry weight (dw), respectively, and the major minerals were Na, K, and Mg. Total phenolics thereof were 67.05 and 38.20 mg of gallic acid equivalents/g extract dw, respectively, mainly p-coumaric acid and quercetin. Both species displayed antioxidant capacity, but S. ramossima was prominent in both the DPPH and ß-carotene bleaching assays. Aflatoxin B1 was detected in S. ramosissima, at 5.21 µg/Kg dw, which may pose a health threat. The Cd and Pb levels in both were low, but the 0.01 mg/Kg Hg in S. perennis alpini met the maximum legal limit established for marine species including algae. Both species exhibit high potential for use in the agro-food, cosmetics, and pharmaceutical sectors, but specific regulations and careful cultivation strategies need to be implemented, in order to minimise contamination risks by mycotoxins and heavy metals.

Cascading effects of Pb on the environmental and symbiotic microbiota and tadpoles' physiology based on field data and laboratory validation

Heavy metal pollution poses a serious threat to ecosystems. Currently, there is a lack of field data that would enable us to gain a systematic understanding of the influences of heavy metals on aquatic ecosystems, especially the interactions between environments and animals. We studied the relationships between the variations in heavy metal concentrations (10 species including Pb in sediments and surface water), the community structure of environmental and symbiotic microbiota, and the gut traits of Bufo gargarizans tadpoles across 16 sampling sites on the Chengdu Plain through rigorous statistical analysis and laboratory validation. The results show that heavy metal concentrations, especially the Pb concentration of the sediment, are linked to the variations in sediment and tadpoles' gut microbiomes but not to water microbiota. For the sediment microbiota, Pb causes a trade-off between the proportions of Burkholderiales and Verrucomicrobiae and affects the methane, sulfide, and nitrate metabolisms. For tadpoles, a high sediment Pb content leads to a low abundance of gut aerobic bacteria and a large relative gut weight under both field and laboratory conditions. In addition, Pb promotes the growth of B. gargarizans tadpoles under laboratory conditions. These effects seem to be beneficial to tadpoles. However, a high Pb content leads to a low abundance of probiotic bacteria (e.g., Verrucomicrobiae, Eubacteriaceae, and Cetobacterium) and a high abundance of pathogenic bacteria in the gut and environment, suggesting potential health risks posed by Pb. Interestingly, there is a causal relationship between Pb-induced variations in sediment and symbiotic microbiotas, and the latter is further linked to the variation in relative gut weight of tadpoles. This suggests a cascading effect of Pb on the ecosystem. In conclusion, our results indicate that among the heavy metals, the Pb in sediment is a critical factor affecting the aquatic ecosystem through an environment-gut-physiology pathway mediated by microbiota.

Enrofloxacin exposure induces anxiety-like behavioral responses in zebrafish by affecting the microbiota-gut-brain axis

The ubiquitous presence of antibiotic residues in aqueous environments poses a great potential threat to aquatic organisms. Nevertheless, the behavioral effects of environmentally realistic levels of antibiotics remain poorly understood in fish species. In this study, the behavioral impacts of enrofloxacin, one of typical fluoroquinolone antibiotics that is frequently detected in aquatic environments, were evaluated by the classic light-dark test (LDT) and novel tank task (NTT) in zebrafish. Furthermore, the effects of enrofloxacin exposure on the microbiota-gut-brain axis were also assessed to reveal potential affecting mechanisms underlying the behavioral abnormality observed. Our results demonstrated that zebrafish exposed to 60 μg/L enrofloxacin for 28 days took significantly longer to enter the stressful area of the testing tank and spent significantly less time there in both the LDT and NTT, indicating abnormal anxiety-like behaviors induced by the exposure. In addition, exposure to enrofloxacin at 6 and 60 μg/L resulted in a significant elevation in Bacteroidetes and a marked decline in the Firmicutes/Bacteroidetes ratio of the gut microbiota. Moreover, the intestinal contents of interleukin 6 (IL-6), tumor necrosis factor-alpha (TNF-α), glucagon-like peptide 1 (GLP-1), and 5-hydroxytryptamine (5-HT) in zebrafish were significantly upregulated, whereas those of plasma adrenocorticotropic hormone (ACTH) and cortisol (COR) were markedly downregulated upon enrofloxacin exposure. Incubation of zebrafish with a high dose of enrofloxacin (60 μg/L) also resulted in evident increases in the contents of corticotropin-releasing hormone (CRH), brain-derived neurotrophic factor (BDNF), and neuropeptide Y (NPY) in the brain. Fortunately, no significant alteration in the expression of glial fibrillary acidic protein (GFAP) was detected in the brain after enrofloxacin exposure. Our findings suggest that the disruption of the microbiota-gut-brain axis may account for enrofloxacin-induced anxiety-like behaviors in zebrafish. Since the disruption of microbiota-gut-brain axis may give rise to various clinical symptoms, the health risk of antibiotic exposure deserves more attention.

Effect of arsenic stress on the intestinal structural integrity and intestinal flora abundance of Cyprinus carpio

Aquatic organisms such as fish can accumulate high concentrations of arsenic (As), which has toxic effects on fish. However, whether the intestinal flora are involved in As damage to fish intestinal tissues and the underlying process are unclear. Common carp (Cyprinus carpio) were exposed to As (2.83 mg/L) in water for 30 days, and blood, muscle, intestine, and intestine samples were collected. Intestinal pathological sections were observed, and the lipopolysaccharide (LPS) levels in serum and the levels of As accumulation and tight junction-related factors in intestinal tissues were measured. The gut microbiota was analysed by 16S rRNA sequencing. The results showed that As treatment decreased the abundance of microbiota, increased the number of harmful bacteria, and decreased the number of beneficial bacteria in the intestine. In our experiment, the top 30 harmful and beneficial bacteria with the highest relative abundance were identified. Among the top 30 harmful and beneficial bacteria, As treatment resulted in a significant (P < 0.05) increase in harmful bacteria (such as Fusobacteriota, Bacteroidota (LPS-producing bacteria), Verrucomicrobiota, Bacteroides, Aeromonas, and Stenotrophomonas) and a significant (P < 0.05) decrease in beneficial bacteria (such as Actinobacteriota, Planctomycetota, Firmicutes, Reyranella, Akkermansia, and Pseudorhodobacter), which further demonstrated that As affects the abundance of intestinal flora. In addition, As exposure increased the LPS level in serum and the abundance of Bacteroidota (LPS-producing bacteria) in the intestine. Bacteroidota exhibits the six highest relative abundance at the phylum level, which indicates that LPS produced by Bacteroidota can increase the LPS level in serum. Additionally, the protein and gene levels of the tight junction markers ZO-1 and occludin in the intestine were reduced by As treatment, which further indicated that As exposure impaired the structural integrity of the intestine. In conclusion, the results obtained in our study indicate that the intestinal flora, LPS, and tight junctions participate in the impairment of the structural integrity of the common carp intestine resulting from As exposure.

Effect of dietary soybean saponin Bb on the growth performance, intestinal nutrient absorption, morphology, microbiota, and immune response in juvenile Chinese soft-shelled turtle (Pelodiscus sinensis)

Soybean meal is widely applied in the aquafeeds due to the limitation of fish meal resources. Numerous studies have manifested that dietary soybean saponin, an anti-nutrient factor in soybean meal, may slow growth and induce intestinal inflammation in aquatic animals, but the possible causes are unclear. The juvenile Pelodiscus sinensis (mean initial body weight: 6.92 ± 0.03 g) were fed basal diet (CON group) and 2.46% soybean saponin Bb-supplemented diet (SAP group) for 35 days to further explore the effects of dietary soybean saponin Bb on the growth performance, apparent digestibility coefficients, intestinal morphology, the gut microbiota, intestinal transporters/channels, and immune-related gene expression. The results indicated that dietary soybean saponin Bb significantly decreased final body weight, specific growth rate, protein deposition ratio, and apparent digestibility coefficients (dry matter, crude protein, and crude lipid) of nutrients in Pelodiscus sinensis, which may be closely correlated with markedly atrophic villus height and increased lamina propria width in the small intestine. In addition, plasma contents of cholesterol, calcium, phosphorus, potassium, lysozyme, and C3 were significantly decreased in the SAP group compared with the control group. Soybean saponin Bb significantly downregulated the mRNA levels of glucose transporter 2, fatty acid binding protein 1 and fatty acid binding protein 2, amino acid transporter 2, b^0,+-type amino acid transporter 1, and sodium-dependent phosphate transport protein 2b in the small intestine. At the same time, the expressions of key transcription factors (STAT1, TBX21, FOS), chemokines (CCL3), cytokines (TNF-α, IL-8), and aquaporins (AQP3, AQP6) in the inflammatory response were increased by soybean saponin Bb in the large intestine of a turtle. Additionally, dietary supplementation of SAP significantly reduced the generic abundance of beneficial bacteria (Lactobacillus, Bifidobacterium, and Bacillus) and harmful bacteria (Helicobacter and Bacteroides). In a nutshell, dietary supplementation of 2.46% soybean saponin not only hindered the growth performance by negatively affecting the macronutrients absorption in the small intestine but also induced an inflammatory response in the large intestine possibly by damaging the intestinal morphology, disturbing the intestinal microbiota and decreasing intestinal epithelial cell membrane permeability.

Anthropogenic disturbance promotes the diversification of antibiotic resistance genes and virulence factors in the gut of plateau pikas (Ochotona curzoniae)

The prevalence and transmission of antibiotic resistance genes (ARGs) and virulence factors (VFs) pose a great threat to public health. The importance of pollution in determining the occurrence of ARGs and VFs in wildlife is poorly understood. Using a metagenomic approach, this study investigates the composition and functional pathways of bacteria, ARGs, and VFs in the gut microbiome of Plateau pikas in regions of medical pollution (MPR), heavy tourist traffic (HTR), and no contamination (NCR). We found that the abundance of probiotic genera (Clostridium, Eubacterium, Faecalibacterium, and Roseburia) were significantly lower in the HTR. The metabolic pathways of replication and repair in the endocrine and nervous systems were significantly enriched in the MPR, whereas endocrine and metabolic diseases were significantly enriched in the NCR. The Shannon and Gini–Simpson α-diversity indices of ARGs were highest in the HTR, and there were significant differences in β-diversity among the three regions. The resistance of ARGs to glycopeptide antibiotics increased significantly in the MPR, whereas the ARGs for aminocoumarins increased significantly in the HTR. The diversity of mobile genetic elements (MGEs) was significantly higher in the MPR than in other regions. We observed a strong positive correlation between ARGs and pathogenic bacteria, and the network structure was the most complex in the MPR. There were significant differences in the β-diversity of VFs among the three regions. Medical pollution led to significant enrichment of fibronectin-binding protein and PhoP, whereas tourism-related pollution (in the HTR) led to significant enrichment of LPS and LplA1. Our study indicates that environmental pollution can affect the structure and function of gut microbes and disseminate ARGs and VFs via horizontal transmission, thereby posing a threat to the health of wild animals.

Inhibition of TNBS-induced intestinal inflammation in crucian carp (Carassius carassius) by oral administration of bioactive Bioactive food derived peptides

Intestinal enteritis is a main issue in crucian carp production which results in massive economic loss. Traditional antibiotics used for disease prevention of crucian carp (Carassius carassius) have been banned, thus an alternative approach needs to be identified. In this study, the bioactive peptide was evaluated as a diet supplement for preventing intestinal inflammation in crucian carp. Intestinal inflammation was induced by intrarectal administration of a 2,4,6-trinitrobenzene sulfonic acid (TNBS) solution. The fish samples were fed with different diets for 14 days. The disease activity index (DAI), which included, fish swimming, food intake, anal inflammation, body surface, and ascites was determined daily. Intestine segments were stained with haematoxylin and eosin (H.E.) for histopathological analysis. The expression of cytokines, including interleukin-1β (IL-1β), interleukin-8 (IL-8), tumor necrosis factor α (TNF-α), and myeloperoxidase (MPO) in crucian carp were determined. In TNBS-induced groups, the DAI scores were dramatically increased compared to the control group. The histopathological analysis showed that the damage of the fish intestine after the injection of TNBS. The relative expression levels of pro-inflammation cytokines (TNF-α, IL-1β, IL-8, MPO) were significantly increased compared to the control group on day 1. In the TNBS-induced group feed with a diet supplemented with bioactive peptide, the symptoms of intestinal inflammation were relieved on day 3 and the mRNA expression levels of pro-inflammation cytokines (TNF-α, IL-1β, IL-8, MPO) were reduced compared to day 1. On day 7, the fish samples enrofloxacin group and bioactive peptide group were recovered from TNBS-induced intestinal inflammation. This study showed that the fish diet supplemented with bioactive peptide could help to prevent and recover from intestinal inflammation. Thus, the bioactive peptide can be used as a replacement for antibiotics to prevent disease in aquaculture production.

Dietary fiber ameliorates lead-induced gut microbiota disturbance and alleviates neuroinflammation

Dietary fiber (DF) is a carbohydrate from the edible part of plants and has the functions of promoting gastrointestinal motility, regulating gut microbiota (GM) and improving health. Lead is a non-essential toxic heavy metal that can accumulate in the environment over time and enter the body through the respiratory tract, skin and gastrointestinal tract. Lead not only causes disturbances in GM but also leads to loss of homeostasis of immune functions, causes neuronal damage and results in neuroinflammation. The scientific literature has reported that DF had anti-inflammatory activity as a natural product. This review highlights the role of DF and its metabolic products in alleviating lead-induced neuroinflammation by inducing changes in the species and quantity of GM and regulating the immune system, providing a potential dietary protective strategy for lead-induced disease. © 2022 Society of Chemical Industry.

Melatonin alleviates lead-induced intestinal epithelial cell pyroptosis in the common carps (Cyprinus carpio) via miR-17-5p/TXNIP axis

Lead (Pb) has been concerned as one of the most severe hazardous contaminants, because it can cause pyroptosis in multiple tissues of mammals and birds. Melatonin (Mel) has attracted much interest for its role in governing intestinal injury via microRNAs (miRNAs). To explore the effect of Mel on Pb exposure-induced intestinal epithelial cell pyroptosis in common carps by regulating miR-17-5p/TXNIP axis, the Pb exposure and Pb-Mel treated models were constructed in vivo. The results elucidated that the suppressed expression of miR-17-5p and intensified level of TXNIP were primarily detected in Pb-exposed gut tissues, and both abolished with Mel addition, along with downregulated Pb-mediated elevated expression of NLRP3, CASP1, IL1β and GSDMD. Additionally, the targeting relationship between miR-17-5p and TXNIP were demonstrated by dual-luciferase reporter assay, and on this basis, miR-17-5p NC, mimic and inhibitor cell models were established. Thereby, Thereby, the expression of TXNIP in the miR-17-5p mimic groups was significant lower in the Pb-exposure but still elevated than the Control group, and the expression of NLRP3 and NLRP3-dependent pyrotposis-related genes performed consistent alterations. Noticeably, the expression of TXNIP suppressed with Mel addition even in the miR-17-5p inhibitor cell model, resulting in the inactivation of NLRP3 inflammasome-dependent pyroptosis. Overall, we draw the conclusion as Mel attenuates Pb-induced intestinal epithelial cell pyroptosis via miR-17-5p/TXNIP axis. The present study provides a novel perspective for toxicological mechanism of Pb, and new insights for the detoxification mechanism of Mel.

Hexavalent Chromium Exposure Induces Intestinal Barrier Damage via Activation of the NF-κB Signaling Pathway and NLRP3 Inflammasome in Ducks

Hexavalent chromium [Cr(VI)] is a dangerous heavy metal which can impair the gastrointestinal system in various species; however, the processes behind Cr(VI)-induced intestinal barrier damage are unknown. Forty-eight healthy 1-day-old ducks were stochastically assigned to four groups and fed a basal ration containing various Cr(VI) dosages for 49 days. Results of the study suggested that Cr(VI) exposure could significantly increase the content of Cr(VI) in the jejunum, increase the level of diamine oxidase (DAO) in serum, affect the production performance, cause histological abnormalities (shortening of the intestinal villi, deepening of the crypt depth, reduction and fragmentation of microvilli) and significantly reduced the mRNA levels of intestinal barrier-related genes (ZO-1, occludin, claudin-1, and MUC2) and protein levels of ZO-1, occludin, cand laudin-1, resulting in intestinal barrier damage. Furthermore, Cr(VI) intake could increase the contents of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-18 (IL-18) but decrease the activities of total superoxide dismutase (T-SOD), catalase (CAT), and glutathione reductase (GR), as well as up-regulate the mRNA levels of TLR4, MyD88, NF-κB, TNFα, IL-6, NLRP3, caspase-1, ASC, IL-1β, and IL-18 and protein levels of TLR4, MyD88, NF-κB, NLRP3, caspase-1, ASC, IL-1β, and IL-18 in the jejunum. In conclusion, Cr(VI) could cause intestinal oxidative damage and inflammation in duck jejunum by activating the NF-κB signaling pathway and the NLRP3 inflammasome.

Sex-specific effects of fluoride and lead exposures on histology, antioxidant physiology, and immune system in the liver of zebrafish (Danio rerio)

Fluoride and Pb are both toxic to organisms; however, their combination effects and the corresponding toxic mechanisms remain unclear. In this study, male and female zebrafish (1:1) were evaluated to understand the effects of F and Pb alone and combined on growth, tissue microstructure, oxidative stress, and immune system functions of the liver. Four different groups and two exposure periods were compared: control group (C group), 80 mg/L fluoride group (F group), 60 mg/L lead group (Pb group), and 80 mg/L fluoride + 60 mg/L lead group (F + Pb group) for 45 and 90 days. The results indicated that F and Pb reduced growth performances; F + Pb treatment inhibited the growth performance traits of male zebrafish more than those of female zebrafish. Histopathological examination revealed large areas with focal necrosis, hepatocytes with karyolysis, and pycnotic nuclei in zebrafish exposed to F and Pb. The oxidative balance indices in the liver in the F and Pb groups were disturbed. F + Pb co-exposure aggravated oxidative stress in a time-dependent manner. The most serious oxidative stress was observed in the male zebrafish of the F + Pb group. Moreover, F and Pb exposure of male zebrafish increased pro-inflammatory and anti-inflammatory cytokines expression, which was decreased after 90 days of exposure. These results demonstrated that both F and Pb could damage the liver via downstream alterations in the activities of immune-related enzymes and in the levels of immune-related genes. F and Pb showed synergistic or additive effects. Male zebrafish were found to be more sensitive to F and Pb than female zebrafish.

Quantifying the Colonization of Environmental Microbes in the Fish Gut: A Case Study of Wild Fish Populations in the Yangtze River

In aquatic animals, gut microbial communities shift with host development and living environments. Understanding the mechanism by which the environment impacts the gut microbial communities of aquatic animals is crucial for assessing and managing aquatic ecosystem health. Here, we proposed a simplified framework for the colonization and dynamics of gut microbial communities. Then, to quantify the colonization of environmental microbes in the wild fish gut, the current study used 16S rRNA gene amplicon sequencing to obtain the structure of the water environmental microbial community and the gut microbial community in 10 wild fish populations (Leiocassis crassilabris, Leiocassis longirostris, Pelteobagrus vachelli, Silurus asotus, Siniperca chuatsi, Coilia brachygnathus, Aristichthys nobilis, Hypophthalmichthys molitrix, Coreius heterodon, and Xenocypris argentea) from the Wuhan section of the Yangtze River, and the relationship of these microbial communities was analyzed. The results identified that in most individuals, approximately 80% of gut microbes [at the operational taxonomic unit (OTU) level] were shared with the water environmental microbial community (except for individuals of Siniperca chuatsi and Coilia brachygnathus, approximately 74%). In approximately 80% of individuals, more than 95% of microbial species (OTUs) in the gut were transient. For fish species, more than 99% of microbial species (OTUs) that were introduced into the gut were transient. Nearly 79% of OTUs and 89% of species of water environmental microbes could be introduced into the fish gut. Driven by the introduction of transient microbes, fishes with similar feeding habits had similar gut microbial communities. The results indicated that for adult wild fishes, most gut microbiota were transient from the environmental microbiota that were related to fish feeding habits. We therefore encourage future research to focus on environmental microbiota monitoring and management to promote the better conservation of aquatic animals. It was important to note that, because of various influence factors, interspecific differences and individual variations on gut microbial community characteristics, the quantification of gut microbes in the current work was approximate rather than accurate. We hope that more comparable research could be conducted to outline the quantitative characteristics of the relationship between gut microbial community and aquatic environment microbial community as soon as possible.

Assessing Fish Immunotoxicity by Means of In Vitro Assays: Are We There Yet?

There is growing awareness that a range of environmental chemicals target the immune system of fish and may compromise the resistance towards infectious pathogens. Existing concepts to assess chemical hazards to fish, however, do not consider immunotoxicity. Over recent years, the application of in vitro assays for ecotoxicological hazard assessment has gained momentum, what leads to the question whether in vitro assays using piscine immune cells might be suitable to evaluate immunotoxic potentials of environmental chemicals to fish. In vitro systems using primary immune cells or immune cells lines have been established from a wide array of fish species and basically from all immune tissues, and in principal these assays should be able to detect chemical impacts on diverse immune functions. In fact, in vitro assays were found to be a valuable tool in investigating the mechanisms and modes of action through which environmental agents interfere with immune cell functions. However, at the current state of knowledge the usefulness of these assays for immunotoxicity screening in the context of chemical hazard assessment appears questionable. This is mainly due to a lack of assay standardization, and an insufficient knowledge of assay performance with respect to false positive or false negative signals for the different toxicant groups and different immune functions. Also the predictivity of the in vitro immunotoxicity assays for the in vivo immunotoxic response of fishes is uncertain. In conclusion, the currently available database is too limited to support the routine application of piscine in vitro assays as screening tool for assessing immunotoxic potentials of environmental chemicals to fish.

Effects of Fumonisin B and Hydrolyzed Fumonisin B on Growth and Intestinal Microbiota in Broilers

Fumonisins are mainly produced by Fusarium verticillioides and proliferatum, which causes a variety of toxicities in humans and animals, including fumonisin Bs (FBs) as the main form. After they are metabolized by plants or microorganisms, modified fumonisins are difficult to detect by conventional methods, which result in an underestimation of their contamination level. Fumonisins widely contaminate maize and maize products, especially in broiler feed. As an economically important food, broilers are often adversely affected by mycotoxins, leading to food safety hazards and high economic losses. However, there are few studies regarding the adverse effects of FBs on broiler growth and health, especially modified FBs. Our data shows that after exposure to FBs or hydrolyzed fumonisin Bs (HFBs), the body weight and tissue weight of broilers decreased significantly, especially the testes. Moreover, they significantly affect the intestinal microbiota and the relative abundance of bacteria from phylum-to-species levels, with the differentially affected bacteria mainly belonging to Firmicutes and Proteobacteria. Our findings suggest that both the parent and hydrolyzed FBs could induce growth retardation, tissue damage and the imbalance of intestinal microbiota in broilers. This indicated that the harmful effects of HFBs cannot be ignored during food safety risk assessment.

Dietary application of Lactococcus lactis alleviates toxicity and regulates gut microbiota in Cyprinus carpio on exposure to heavy metals mixture

Heavy metals (HMs) contaminated fish is a threat to humans when consumed. Dietary probiotics have evolved as a successful HMs removal approach. In this study, probiotics Enterococcus (EC) sp. and Lactococcus (LC) sp. were evaluated for toxicity alleviation and gut microbiota maintenance in Cyprinus carpio (single and combined approach) on Cr, Cd, and Cu mixture (0.8 mg/L and 1.6 mg/L) exposure (28 days). HMs removal, oxidative stress, cytokines response, histology, and gut microbiota were investigated. LC alone showed remarkable HMs removal for Cr (62.28%-87.57%), Cd (89%-90.42%), and Cu (72%-88%) than LC + EC. Probiotics up-regulated superoxide dismutase and total protein levels, while decreased the activity of malondialdehyde than the control. Pro-inflammatory cytokine (TNF-α) and chemokine (IL-8) expressions were higher at 1.6 mg/L concentration, whereas anti-inflammatory cytokine (IL-10) was higher in the 0.8 mg/L group. LC mitigated the histological alterations of gills, kidneys, and intestines, particularly at the lower concentration. Sequencing results revealed that Proteobacteria (44%-61%) was the most dominant phylum in all groups, followed by Fusobacteria (34%-36%) at 0.8 mg/L and Firmicutes (19%-34%) at 1.6 mg/L. The current study presented LC and EC potential separately and in combination to countermeasure HMs mixture induced toxicity and gut microbial dysbiosis, in which the conjoint group was less effective.

Lead impaired immune function and tissue integrity in yellow catfish (Peltobargus fulvidraco) by mediating oxidative stress, inflammatory response and apoptosis

Lead (Pb) widely exists in the water environment and has severe toxic effects on aquatic organisms. The yellow catfish (Pelteobagrus fulvidraco) is one of the most important commercial species in China, and moreover, its natural populations are declining with the degradation of environmental water quality. However, little is known about the toxic effects of Pb on its immune organs. This study was performed to determine waterborne Pb exposure on bioaccumulation, histomorphology, antioxidant status, apoptotic and immune response in the head kidney and spleen of yellow catfish. Experimental fish were randomly allocated into twelve tanks (3 tanks per group), and the Pb concentrations of the four groups were 0, 5, 50, and 500 μg/L, respectively. The results reflected that the Pb bioaccumulation of the head kidney and spleen increased with increasing Pb exposure dose and time. Severe histological alterations in the head kidney and spleen were observed at concentration 500 ug/L. With increasing Pb exposure concentrations, the plasma activity of superoxide dismutase (SOD) and catalase (CAT) significantly increased after exposure 7 days and 14 days, and the levels significantly decreased after exposure 28 days. The change trend of glutathione (GSH) levels was opposite to that of SOD and CAT at corresponding exposure time. The plasma malondialdehyde (MDA) levels together with the activities of plasma alkaline phosphatase (AKP) and acid phosphatase (ACP) increased significantly with the increasing Pb concentrations. In contrast, the levels of lysozyme (LYZ), complement 3 (C3) and immunoglobulin M (IgM) decreased significantly with increasing Pb concentrations. Moreover, Pb exposure induced transcriptional upregulation of heat shock protein 70 (hsp70), metallothionein (mt), sod, cat, interleukin-10 (il-10), transforming growth factor-β (tgf-β), and tumor necrosis factor-α (tnf-α), bcl-2-associated X protein (bax), and cysteinyl aspartate specific proteinase -9 (caspase-9), genes in the head kidney and spleen tissues, while downregulating the levels of the lyz, c3, igm and B-cell lymphoma-2 (bcl-2) genes. Our data provide evidence that Pb impaired immune function and tissue integrity in yellow catfish through oxidative stress, inflammatory and apoptosis, and the results can serve as reference data to better protect water environments from Pb eco-toxicants.

Bisdemethoxycurcumin attenuates lipopolysaccharide-induced intestinal damage through improving barrier integrity, suppressing inflammation, and modulating gut microbiota in broilers

Bisdemethoxycurcumin has good antioxidant and anti-inflammatory effects and has been widely used as food and feed supplements in the form of curcuminoids. However, the beneficial effect of individual bisdemethoxycurcumin on preventing lipopolysaccharide (LPS)-induced inflamed intestinal damage is unclear. The present study aimed to investigate whether dietary bisdemethoxycurcumin supplementation could attenuate LPS-induced intestinal damage and alteration of cecal microbiota in broiler chickens. In total, 320 one-day-old male Arbor Acres broiler chickens with a similar weight were randomly divided into four treatments. The treatments were designed as a 2 × 2 factorial arrangement: basal diet (CON); 150 mg/kg bisdemethoxycurcumin diet (BUR); LPS challenge + basal diet (LPS); LPS challenge + 150 mg/kg bisdemethoxycurcumin diet (L-BUR). Results showed that dietary bisdemethoxycurcumin supplementation attenuated the LPS-induced decrease of average daily feed intake. LPS challenge compromised the intestinal morphology and disrupted the intestinal tight junction barrier. Dietary bisdemethoxycurcumin supplementation significantly increased villus length:crypt depth ratio and upregulated the mRNA expression of intestinal tight junction proteins. Moreover, a remarkably reduced mRNA expression of inflammatory mediators was observed following bisdemethoxycurcumin supplementation. The cecal microbiota analysis showed that bisdemethoxycurcumin supplementation increased the relative abundance of the genus Faecalibacterium while decreased the relative abundance of the genera Bacteroides and Subdoligranulum. In conclusion, dietary bisdemethoxycurcumin supplementation could counteract LPS-induced inflamed intestinal damage in broiler chickens by improving intestinal morphology, maintaining intestinal tight junction, downregulating pro-inflammatory mediators, and restoring cecal microbiota.

Effects of Nisin, Cecropin, and Penthorum chinense Pursh on the Intestinal Microbiome of Common Carp (Cyprinus carpio)

Following a ban on antibiotic use in the feed industry, trials on the effects of various immunostimulants (prebiotics, probiotics, antimicrobial peptides [AMPs], and herbs) on the survival, growth, immunity, and disease control of farmed fish in aquaculture are being rapidly conducted. The wide variety of microbes with roles in nutrition, metabolism, and immunity in the fish intestine is the primary factor affecting the fermentability and functionality of dietary immunostimulants. For this reason, the dynamic interactions between immunostimulants and the intestinal microbiome may influence fish health. In this study, the effects of two agriculturally important AMPs (nisin and cecropin) and one herb (Penthorum chinense) on the gut microbiome of common carp were investigated, using 16S rDNA high-throughput sequencing. The results suggest that all three substances can alter the richness, diversity, and composition of the intestinal microbiota of common carp. P. chinense had a similar effect on the gut microbiota of common carp to that of nisin, and both promoted more striking changes in the gut microbiota community than did cecropin. The relative abundance of Proteobacteria was lower in the nisin and P. chinense groups than in the control and cecropin groups. The relative abundance of Bacteroidetes in the nisin, cecropin, and P. chinense groups was markedly increased, compared with that of the control group. Additionally, nisin, cecropin, and P. chinense showed obvious anti-inflammatory effects on the fish intestine, which was reflected by significantly increasing the expression levels of two anti-inflammatory cytokines IL-10 and TGF-β. Some digestive enzyme activities in the fish intestine were also significantly enhanced by supplementing these three substances in feeds.

Dietary L-arginine supplementation of tilapia (Oreochromis niloticus) alters the microbial population and activates intestinal fatty acid oxidation

Currently, little is known about the function of L-arginine in the homeostasis of intestinal lipid metabolism. This study was conducted to test the hypothesis that dietary L-arginine supplementation may alter intestinal microbiota and lipid metabolism in tilapia. Tilapia were fed a basal diet (containing 16.9 g L-arginine per kilogram diets) or the basal diet supplemented with 1% or 2% L-arginine for 8 wks. In the present study, we found that dietary supplementation with 1% or 2% L-arginine induced a shift in the community structure of gut microbiota, as showed by increased (p < 0.05) α-diversity, altered (p < 0.05) β-diversity and function profile. This finding coincided with decreased lipid accretion in the intestine of tilapia, which was associated with an enhancement in mRNA levels for peroxisome proliferator-activated receptor α (Pparα), acyl-coenzyme a oxidase 1 (Acox1), and peroxisome proliferator-activated receptor γ coactivator-1α (Pgc-1α). Using intestinal epithelial cell culture, we demonstrated that the lipid-lowering effect of L-arginine was mainly mediated by activating the AMP-activated protein kinase (AMPK) signaling pathway, carnitine palmitoyltransferase 1 (CPT1), and PPARα, as well as mRNA levels for Acox1 and Acox2. Collectively, our results suggest that dietary L-arginine supplementation of tilapia changed the intestinal microbiota and activated intestinal fatty acid oxidation. However, future studies are warranted to determine the relationship between microbiota and lipid metabolism in the intestine.

Effects of Dietary Saccharomyces cerevisiae YFI-SC2 on the Growth Performance, Intestinal Morphology, Immune Parameters, Intestinal Microbiota, and Disease Resistance of Crayfish (Procambarus clarkia)

The present study aimed to evaluate the effect of the dietary supplementation of Saccharomyces cerevisiae YFI-SC2 on the growth performance, intestinal morphology, immune parameters, intestinal microbiota, and disease resistance of crayfish (Procambarus clarkia). Crayfish were randomly assigned to six different boxes and two different groups in triplicate. The control group received a basal diet and the treatment group received a diet containing S. cerevisiae at 10⁷ CFU/g. After feeding for 28 days, crayfish of the treatment group exhibited a significantly better weight gain ratio (WGR) and a specific growth rate (SGR) (p < 0.05) than crayfish of the control group. Compared to the treatment group, the control group intestines showed an oedema connective tissue layer and a weak muscle layer. For immune-related genes, Crustin2 expression was similar between the groups, whereas Lysozyme and prophenoloxidase from treatment group expression levels were upregulated significantly (p < 0.05) after 14 and 28 days of feeding. Prophenoloxidase showed the highest expression, with 10.5- and 8.2-fold higher expression than in the control group at 14 and 28 days, respectively. The intestinal microbiota community structure was markedly different between the two groups. After 14 and 28 days of feeding, the relative abundance of Cetobacterium and Lactobacillus increased, whereas Citrobacter and Bacteroides decreased in the treatment group compared with that of the control group. The challenge test showed that crayfish of the treatment group had a significantly enhanced resistance against Citrobacter freundii (p < 0.05). Our results suggest that a S. cerevisiae-containing diet positively influenced the health status, immune parameters, intestinal microbiota composition, and disease resistance of crayfish.

Interactions Between Commensal Microbiota and Mucosal Immunity in Teleost Fish During Viral Infection With SVCV

The mucosa of vertebrates is a particularly complex but dynamic environment in which the host constantly interacts with trillions of commensal microorganisms and pathogens. Although the internal and external mucosal microbiomes with immune defense of mammals have been well investigated, the relationship between mucosal microbes and their host’s immune responses has not been systematically understood in the early vertebrates. In this study, we compared the composition and distribution of mucosal microbiota in common carp (Cyprinus carpio), and found that there were significant differences of microbiota between in the internal (gut) and external mucosal (buccal mucosa, gills and skin) tissues. Next, we successfully constructed an infection model with spring viremia of carp virus (SVCV). Specifically, following viral infection, the immune and antiviral related genes showed different up-regulation in all selected mucosal tissues while significant morphological changes were only found in external tissues including buccal mucosa, gills and skin. Using 16S rRNA gene sequence, we revealed that the abundance of Proteobacteria in mucosal tissues including buccal mucosa, gills and gut showed increased trend after viral infection, whereas the abundance of Fusobacteria significantly decreased in gut. In addition, the loss of dominant commensal microorganisms and increased colonization of opportunistic bacteria were discovered in the mucosal surfaces indicating that a secondary bacterial infection might occur in these mucosal tissues after viral infection. Overall, our results firstly point out the distribution of internal and external mucosal microbiota and analyze the changes of mucosal microbiota in common carp after SVCV infection, which may indicated that the potential role of mucosal microbiota in the antiviral process in early vertebrates.

Arecanut (Areca catechu L.) Seed Polyphenol-Ameliorated Osteoporosis by Altering Gut Microbiome via LYZ and the Immune System in Estrogen-Deficient Rats

Polyphenol can improve osteoporosis and is closely associated with gut microbiota, while the mechanism and the relationship among polyphenol, osteoporosis, and gut microbiota colonization remain unclear. Here, an osteoporosis rat model established by ovariectomy was employed to investigate the improving mechanism of arecanut (Areca catechu L.) seed polyphenol (ACP) on osteoporosis by regulating gut microbiota. We analyzed the bone microstructure, Paneth cells, regulating microbial protein (lysozyme (LYZ)), proinflammatory cytokines, macrophage infiltration levels, and gut microbial communities in a rat. ACP improved the trabecular microstructure compared to OVX, including the increased trabecular number (Tb.N) (P < 0.01) and trabecular thickness (Tb.Th) (P < 0.001) and decreased trabecular separation (Tb.Sp) (P < 0.01). At the phylum level, Bacteroidetes was increased after ovariectomy (P < 0.001) and Firmicutes and Proteobacteria were increased in ACP (P < 0.001). Antiosteoporosis groups with lower LYZ and Paneth cells (P < 0.001) showed that the microbiota Alistipes, which have a negative effect on bone metabolism were decreased in ACP (P < 0.001). Altogether, these studies showed that the estrogen deficiency could induce the shedding of Paneth cells, which leads to the decrease of LYZ, while ACP could increase the LYZ expression by maintaining the population of Paneth cells in an estrogen-deficient host, which were implicated in gut microbiota regulation and improved osteoporosis by controlling the inflammatory reaction.