Important Metabolites Research Articles

Integrative analysis of microRNAs and mRNAs reveals the regulatory networks of triterpenoid saponin metabolism in Soapberry (Sapindus mukorossi Gaertn.).

Triterpenoid saponin are important secondary metabolites and bioactive constituents of soapberry (Sapindus mukorossi Gaertn.) and are widely used in medicine and toiletry products. However, little is known about the roles of miRNAs in the regulation of triterpenoid saponin biosynthesis in soapberry. In this study, a total of 3036 miRNAs were identified, of which 1372 miRNAs were differentially expressed at different stages of pericarp development. Important KEGG pathways, such as terpenoid backbone biosynthesis, sesquiterpenoid and triterpenoid biosynthesis, and basal transcription factors were highlighted, as well the roles of some key miRNAs, such as ath-miR5021, han-miR3630-3p, and ppe-miR858, which may play important roles in regulating triterpenoid saponin biosynthesis. In addition, 58 miRNAs might participate in saponin biosynthesis pathways by predicting the targets of those miRNAs to 53 saponin biosynthesis structural genes. And 75 miRNAs were identified to potentially play vital role in saponin accumulation by targeting transcript factor genes, bHLH, bZIP, ERF, MYB, and WRKY, respectively, which are candidate regulatory genes in the pathway of saponin biosynthesis. The results of weighted gene coexpression network analysis (WGCNA) suggested that two saponin-specific miRNA modules and 10 hub miRNAs may participate in saponin biosynthesis. Furthermore, multiple miRNA-mRNA regulatory networks potentially involved in saponin biosynthesis were generated, e.g., ath-miR5021-SmIDI2/SmGPS5/SmbAS1/SmCYP71D-3/SmUGT74G-2, han-miR3630-3p-SmCYP71A-14/SmbHLH54/SmMYB135/SmWRKY32, and ppe-miR858-SmMYB5/SmMYB32. qRT-PCR analysis validated the expression patterns of nine miRNAs and 12 corresponding target genes. This study represents the first comprehensive analysis of miRNAs in soapberry and lays the foundation for further understanding of miRNA-based regulation in triterpenoid saponin biosynthesis.

Functional Endophytes Regulating Plant Secondary Metabolism: Current Status, Prospects and Applications.

Endophytes, which are widely found in host plants and have no harmful effects, are a vital biological resource. Plant endophytes promote plant growth and enhance plants' resistance to diseases, pests, and environmental stresses. In addition, they enhance the synthesis of important secondary metabolites in plants and improve the potential applicability of plants in agriculture, medicine, food, and horticulture. In this review, we summarize the recent progress in understanding the interaction between endophytes and plants and summarize the construction of synthetic microbial communities (SynComs) and metaomics analysis of the interaction between endophytes and plants. The application and development prospects of endophytes in agriculture, medicine, and other industries are also discussed to provide a reference for further study of the interaction between endophytes and plants and further development and utilization of endophytes.

Synthesis of novel thiazoles bearing lupeol derivatives as potent anticancer and anti-inflammatory agents

Lupeol is one of the most important metabolite in the class of terpenoids and possess excellent anticancer, anti-inflammatory, anti-diabetic activities etc. In the present study, the different thiazoles and oxazoles bearing lupeol derivatives were prepared to enhance their biological activity. Initially, the in vitro cytotoxic activity results showed that the synthesized lupeol derivatives (9a–9j and 10a–10e) showed significant activity against various cancer cells and the compounds 9h and 10b exhibited excellent activity against CAL27 cells. Further, these compounds 9h and 10b arrest the cell cycle at S phase and induce the late apoptosis in CAL27 cells by downregulating the BcL2 and vimentin expression and upregulating the Bax gene expression. Moreover, the lupeol derivatives showed dose-dependent anti-inflammatory activity by inhibiting the secretion of IL-6 cytokines in LPS-induced Raw 264.7 cells. Together, these results clearly indicated that the thiazoles and oxazoles bearing lupeol derivatives can used as chemotherapeutic drugs against cancer and inflammatory diseases.

Integrative metabolomics and network pharmacology to study the preventative impact of dioscin treatment on hyperuricemia.

This work aims to combine network pharmacology and metabolomics to explore the mechanism of action of dioscin on hyperuricemia (HUA). The preventative impact of dioscin on HUA and its putative mechanism were examined using network pharmacological analysis and metabonomics. Network pharmacology study further pointed out the potential targets of dioscin after a review of the relevant biomarker pathways discovered by metabolomic analysis. Molecular docking was then used to examine how the active chemicals interacted with the target proteins. The therapeutic effect of dioscin on HUA was shown to be mediated by 13 potentially important metabolites as a result of metabonomic research. Most of these metabolites are regulated after dioscin therapy to help patients recover. Based on network pharmacology, we identified 10 central genes, which is partly in agreement with metabolomics data. Using metabolomics and network pharmacology, this study investigated the primary targets and mechanisms of dioscin in the treatment of HUA. It is advantageous that dioscin has been developed as an additional drug for the treatment of HUA.

Metabolomics and bioinformatic analyses to determine the effects of oxygen exposure within longissimus lumborum steak on beef discoloration.

Meat discoloration starts from the interior and spreads to oxymyoglobin layer on the surface. The effects of oxygen exposure within a steak on the metabolome have not been evaluated. Therefore, the objective of this study was to evaluate the impact of oxygen exposure on the metabolome of the longissimus lumborum muscle. Six United States Department of Agriculture (USDA) Low Choice beef strip loins were sliced into steaks (1.91-cm) and packaged in polyvinyl chloride overwrap trays for 3 or 6 d of retail display. The oxygen exposed (OE) surface was the display surface during retail, and the non-oxygen exposed (NOE) surface was the intact interior muscle. The instrumental color was evaluated using a HunterLab MiniScan spectrophotometer. To analyze the NOE surface on days 3 and 6, steaks were sliced parallel to the OE surface to expose the NOE surface. Metmyoglobin reducing ability (MRA) was determined by nitrite-induced metmyoglobin reduction. A gas chromatography-mass spectrometry was used to identify metabolites. The a* values of steaks decreased (P < 0.05) with display time. MRA was greater (P < 0.05) in the NOE surface compared with the OE surface on days 3 and 6. The KEGG pathway analysis indicated the tricarboxylic acid (TCA) cycle, pentose and glucuronate interconversions, phenylalanine, tyrosine, and tryptophan metabolism were influenced by the oxygen exposure. The decrease in abundance of succinate from days 0 to 6 during retail display aligned with a decline in redness during display. Furthermore, citric acid and gluconic acid were indicated as important metabolites affected by oxygen exposure and retail display based on the variable importance in the projection in the PLS-DA plot. Citric acid was lower in the NOE surface than the OE surface on day 6 of retail display, which could relate to the formation of succinate for extended oxidative stability. Greater alpha-tocopherol (P < 0.05) in the NOE surface supported less oxidative changes compared to the OE surface during retail display. These results indicate the presence of oxygen can influence metabolite profile and promote migration of the metmyoglobin layer from interior to surface.

Značaj prevencije hiperhomocisteinemije kao faktora rizika za kardiovaskularne bolesti

Introduction. Homocysteine is an amino acid that is formed in the metabolism of methionine as the quantitatively most important metabolite. Its chemical structure has been known for 90 years and its biological roles are still being investigated. Under normal conditions, homocysteine is present in plasma at the concentration of 5 - 9 mmol/l. When the cell capacity for homocysteine is reached, it is transported to the extracellular space, until the intracellular level is normalized. If the cell is unable to reach the required levels of homocysteine, it accumulates in the blood and hyperhomocysteinemia occurs. Discussion. It has been determined that many factors, such as congenital enzyme deficiency, age, sex, inadequate diet (vitamin B complex deficiency) increase the level of homocysteine in the blood. Impaired kidney function, diabetes, hyperthyroidism, as well as many medications, can have an effect on homecysteinemia. Increased concentration of homocysteine in the blood accelerates the process of atherosclerosis by several different mechanisms and represents an independent risk factor for the occurrence of cardiovascular diseases and adverse cerebral events. The prevalence of hyperhomocysteinemia is estimated at 5% in the general population and 13 - 47% among patients with symptomatic atherosclerotic vascular disease. Conclusion. For these reasons, the level of homocysteine in the blood should be monitored and corrective measures should be implemented, which include sufficient intake of folic acid, vitamins B12 and B6, in doses that depend on fasting homocysteine levels and after the methionine load test.

A fluorometric assay for high-throughput phosphite quantitation in biological and environmental matrices.

Phosphite, the anion of phosphorus acid, is an important metabolite in the global biogeochemical phosphorus cycle and a phosphorus species with unique agricultural properties. As such, methods for detecting phosphite quantitatively and selectively are critical to evidencing phosphorus redox chemistry. Here, we present a fluorescence-based assay for phosphite, utilizing the NAD+-dependent oxidation of phosphite by phosphite dehydrogenase and the subsequent reduction of resazurin to resorufin. With the application of a thermostable phosphite dehydrogenase, a medium-invariant analytical approach, and novel sample preparation methods, the assay is capable of rapid and accurate phosphite quantification with a 3 μM limit of detection in a wide array of biologically- and environmentally-relevant matrices, including bacterial and archaeal cell lysate, seawater, anaerobic digester sludge, and plant tissue. We demonstrate the utility of the assay by quantitating phosphite uptake in a model crop plant in the presence or absence of a phosphite-oxidising strain of Pseudomonas stutzeri as a soil additive, establishing this bacterium as an efficient phosphite converting biofertilizer.

Citric Acid-Based Intrinsic Band-Shifting Photoluminescent Materials.

Citric acid, an important metabolite with abundant reactive groups, has been demonstrated as a promising starting material to synthesize diverse photoluminescent materials including small molecules, polymers, and carbon dots. The unique citrate chemistry enables the development of a series of citric acid-based molecules and nanomaterials with intriguing intrinsic band-shifting behavior, where the emission wavelength shifts as the excitation wavelength increases, ideal for chromatic imaging and many other applications. In this review, we discuss the concept of "intrinsic band-shifting photoluminescent materials", introduce the recent advances in citric acid-based intrinsic band-shifting materials, and discuss their potential applications such as chromatic imaging and multimodal sensing. It is our hope that the insightful and forward-thinking discussion in this review will spur the innovation and applications of the unique band-shifting photoluminescent materials.

Diversity of Pleurotus spp. (Agaricomycetes) and Their Metabolites of Nutraceutical and Therapeutic Importance.

Pleurotus spp. have been gaining popularity as a source for the creation of functional foods, nutraceuticals and novel pharmaceuticals. Despite Pleurotus is a specious genus including 208 legitimate species, only a few of them such as P. ostreatus are commercially accessible. The genetic and metabolic diversity of Pleurotus both at specific and subspecific level is therefore of main concern for many researchers. In addition to the conventional morphological approach, molecular and biochemical markers have been greatly contributing to investigate these issues. In this study, samples from six Pleurotus species (P. eryngii is represented by three varieties) were molecularly identified and the phylogeny was inferred to assess the relationships between the various taxa. Strains in pure culture obtained from 6 out of 7 species were cultivated as mycelium in vitro to investigate the metabolites by untargeted LC-MS/MS-based metabolomics. The results pointed out species-specific metabolite patterns and highlighted a clear difference between the P. eryngii group and P. ostreatus, although the latter appears more versatile depending on the strain. This is the first study pointing out and comparing different metabolite patterns in Italian samples of Pleurotus species, including P. eryngii varieties.

Role of proline in regulating turfgrass tolerance to abiotic stress

Turfgrasses used on golf courses, sports fields and in urban landscapes have significant ecological and economic values. Various abiotic stresses are crucial in limiting the growth and development of turfgrass. As an important amino acid metabolite, proline can act as a signal to trigger plant responses to stress. Proline accumulation is not only a stress signal, but also alleviates plant damage by maintaining photosynthesis and the activities of antioxidant enzymes and the levels of non-enzymatic antioxidant compounds, thus reducing reactive oxygen species content, and regulating osmosis. A better understanding of mechanisms of proline response to abiotic stress in turfgrass is vital for the development of stress-tolerant germplasm. This review summarizes research progress into the role of proline in regulating growth and physiological and molecular adaptations to abiotic stress, with emphasis on drought, salt and temperature tolerance.

Population whole-genome resequencing reveals the phylogenetic relationships and population structure of four Hunan typical tea landraces

Hunan located at the evolutionary transitional zone edge of the Yunnan-Guizhou plateau, tea germplasms are abundant. At present, although morphological, enzymological and molecular markers have been used to study the genetic relationship of these tea germplasms. However, due to the complexity of the genetic background of tea germplasm resources, the evolution history and taxonomy of Hunan tea germplasm is still unclear. In this study, four Hunan tea landraces from the evolutionary transitional zone were collected, including 9 'Chengbu Dongcha' (CBDC), 8 'Jianghua Kucha' (JHKC), 11 'Rucheng Baimao' (RCBM) and 8 'Anhua Yuntai' (AHYT). We used whole-genome re-sequencing to identify genetic variation, phylogenetic placement, and population structure among the four tea landraces and then scanned the genome for regions related to population potential selective. Across the samples, we identified an average of 1.38 million (M) SNPs and 6.82 × 10³ INDELs. Based on the high-quality SNPs, we performed neighbor-joining phylogenetic tree, population structure, and principal component analysis, all of which supported that the 36 tea germplasms could been divided into two groups, CBDC and AHYT were clustered into a group, and RCBM and JHKC were clustered into another group. With CBDC, JHKC, and RCBM as control, 407, 380, and 147 selected genes were identified in AHYT, respectively, were in the top 5% of F_ST and Log₂^Ratioθπ scores. The identified genes are mainly involved in stress tolerance, biosynthesis of important secondary metabolites, adaptability, and yield. These results will be helpful in the classification of tea germplasms and investigating selection–related genes.

Antioxidants and cardioprotective effects of ethyl acetate fraction of Canavalia rosea leaves in myocardial ischemia-reperfusion injury.

Different degrees in the biological activities of Canavalia rosea had been previously reported . In this study, our group assessed the cardioprotective effects of the ethyl acetate fraction (EAcF) of the Canavalia rosea leaves. Firstly, it was confirmed, by in vitro approach, that the EAcF has high antioxidant properties due to the presence of important secondary metabolites, as flavonoids. In order to explore their potential protector against cardiovascular disorders, hearts were previously perfused with EAcF (300 μg.mL-1) and submitted to the global ischemia followed by reperfusion in Langendorff system. The present findings have demonstrated that EAcF restored the left ventricular developed pressure and decreased the arrhythmias severity index. Furthermore, EAcF significantly increased the glutathiones peroxidase activity with decreased malondialdehyde and creatine kinase levels. EAcF was effective upon neither the superoxide dismutase, glutationes reductase nor the catalase activities. In addition, the Western blot analysis revealed that ischemia-reperfusion injury significantly upregulates caspase 3 protein expression, while EAcF abolishes this effect. These results provide evidence that the EAcF reestablishes the cardiac contractility and prevents arrhythmias; it is suggested that EAcF could be used to reduce injury caused by cardiac reperfusion. However more clinical studies should be performed, before applying it in the clinic.

Antibacterial activity and improvement of the oxidative stability of soybean oil by 4-hydroxybenzyl isothiocyanate from white mustard seeds

4-Hydroxybenzyl isothiocyanate (4-HBITC) is one of the most important secondary metabolite products in white mustard seeds. The antibacterial activity and inhibition of lipid oxidation of 4-HBITC were investigated. The results indicated that 4-HBITC had a significant antibacterial effect on Escherichia coli, Staphylococcus aureus, and Salmonella typhimurium, and its effect on gram-positive bacteria was superior to that on gram-negative bacteria. The combination of 4-HBITC with citric acid or ascorbic acid had a better antibacterial effect than adding them alone. The antibacterial mechanism of 4-HBITC to affect the metabolic activity rather than the integrity or the permeability of cell membranes was identified. In addition, white mustard seed extract which contains 4-HBITC was found to extend the oxidative stability of soybean oil, and this effect was also improved after the combination of 4-HBITC with citric acid. These results indicated that 4-HBITC and white mustard seed extract have potential for application as a natural preservatives in food and for improving the oxidative stability of edible oils.

Functional analysis of phosphoethanolamine N-methyltransferase in plants and parasites: Essential S-adenosylmethionine-dependent methyltransferase in choline and phospholipid metabolism.

Phospholipids play an essential role as a barrier between cell content and the extracellular environment and regulate various cell signaling processes. Phosphatidylcholine (PtdCho) is one of the most abundant phospholipids in plant, animal, and some prokaryote cell membranes. In plants and some parasites, the biosynthesis of PtdCho begins with the amino acid serine, followed mainly through a phosphoethanolamine N-methyltransferase (PMT)-mediated biosynthetic pathway to phosphocholine (pCho). Because the PMT-mediated pathway, referred to as the phosphobase methylation pathway, produces a series of important primary and specialized metabolites for plant development and stress response, understanding the PMT enzyme is a key aspect of engineering plants with improved stress tolerance and fortified nutrients. Importantly, given the very limited phylogenetic distribution of PMTs, functional analysis and the identification of inhibitors targeting PMTs have potential and positive impacts in humans and in veterinary and agricultural fields. Here, we describe detailed basic knowledge and practical research methods to enable the systematic study of the biochemical and biophysical functions of PMT. The research methods described in this chapter are also applicable to the studies of other ubiquitous S-adenosyl-l-methionine (SAM)-dependent methyltransferases in all kingdoms.

The TT2-type MYB transcription factor JrMYB12 positively regulates proanthocyanidin biosynthesis in red walnut

Proanthocyanidins (PAs) are important phenolic secondary metabolites. Red walnut ‘RW-1’ is rich in PAs, but little information is available on the regulation mechanism of PA biosynthesis. Here, we reported a MYB transcription factor from ‘RW-1’, designated JrMYB12, which acted as a positive regulator in PAs accumulation. Sequence alignment showed JrMYB12 protein belongs to TT2-type R2R3 MYB transcription factor because of its TT2 domain. The expression of JrMYB12 gene was positively correlated with the accumulation of PAs and the expressions of PA-related genes (JrLAR and JrANR) in red walnut. JrMYB12 protein localized to the nuclear and showed transcriptional self-activation activity. The expression of key genes related to PA biosynthesis (AtCHS, AtDFR, AtANS, and AtANR) was up-regulated in transgenic JrMYB12 overexpression Arabidopsis lines, and the content of PAs in leaves and seed coat increased significantly. However, the overexpression of JrMYB12 gene did not cause the change of the key anthocyanin related gene AtUFGT expression in Arabidopsis. Yeast two-hybrid showed that JrMYB12 and JrbHLH42 proteins had obvious interaction, and dual-luciferase assays showed that the two proteins could form a complex to significantly enhance the promoter activity of PAs biosynthesis structural genes JrLAR and JrANR alone or together. Collectively, our research revealed the regulatory mechanism of PA biosynthesis in red walnut, and will be useful for manipulating proanthocyanidins accumulation in walnut and other plants.

1H NMR Using Metabolic Study in Body Fluids for Diagnosis of Cryptococcal Meningitis in Adults.

Cryptococcal meningitis is considered to affect HIV patients and those with impaired immune systems. Early identification and treatment are the keys to decreasing morbidity and mortality related to CM. Using 1H NMR spectroscopy, a prospective case-control study will assess the metabolic profile of adults' serum, urine, and CSF. The present multicentric study was conducted at Lucknow. The study included 150 participants, out of which there were 31 cryptococcal meningitis cases, 34 positive meningitis controls, and the rest, 85, were disease controls. The discriminant function analysis (DFA) of the three biofluids was used to find significant metabolites between the cases and the control group collectively. A group categorization between control group and the cases in serum, urine, and CSF samples was also made possible by the NMR spectral bin-based orthogonal signal correction and principal component analysis score plots of important metabolites produced from DFA. The cases group had a higher proportion of patients with higher CSF protein levels than the positive control group (BM and TM). Acetone was found among urine samples in both control samples, i.e., positive and negative. This is the first study to explore biomarkers in serum, urine, and CSF in addition to radiological features and clinical symptoms. Hence, a quick, non-invasive prognosis and diagnosis of cryptococcal meningitis in adults can be made using clinical and microbiological investigation, as well as metabolomic analysis of urine samples. This study shows that urine can be used as a biofluid to differentiate between Cryptococcus meningitis in adults. However, when compared to the negative control, our sample size was significantly smaller, necessitating further confirmation on a larger sample size.

A solid phase extraction column based on SiO2@ZIF-8 for efficient analysis of domoic acid toxins in the seawater environment: experiments and DFT calculations on adsorption behaviour.

Algal toxins are important metabolites of toxic harmful algal blooms (HABs), and their qualitative and qualitative detection can serve as early warning indicators for toxic HABs, complementing traditional HAB monitoring and improving the accuracy of early warning. Therefore, this work took the detection of domoic acid (DA) as an example and prepared zeolitic imidazolate framework-8 (ZIF-8) with high enrichment performance and high water stability and its core-shell composite material SiO2@ZIF-8 as an adsorbent filler. Density functional theory (DFT) calculations and interference experiments verified that Zn2+ on SiO2@ZIF-8 played a crucial role in enriching DA on SiO2@ZIF-8. By using it as a solid-phase extraction (SPE) filler, it showed excellent performance compared with other SPE columns (C18/HLB/SAX/ZIF-8). Therefore, the SiO2@ZIF-8 column was coupled to high-performance liquid chromatography-mass spectrometry (SPE-HPLC-MS/MS) to establish a highly sensitive detection method for algal toxins in seawater, which had a wide linear range (12.0-5000.0 ng L-1), good reproducibility (RSD) and low limit of detection (4.0 ng L-1), and realized the monitoring of trace DA in the Pingtan sea area of Fujian Province from 2021 to 2022. By comparing other HAB early warning indicators such as salinity and pH and combining them with the information released by the Fujian Provincial Ocean and Fisheries Bureau, the content of DA in seawater measured by the established SPE-HPLC-MS/MS method can provide reference information for HAB monitoring and early warning.

Hepatotoxicity and mechanism of Rhododendri Mollis Flos based on zebrafish model

This study used the zebrafish model to explore the hepatotoxicity of Rhododendri Mollis Flos(RMF). The mortality was calculated according to the number of the survival of zebrafish larvae 4 days after fertilization under different concentration of RMF, and the dose-toxicity curve was fitted to preliminarily evaluate the toxicity of RMF. The liver phenotypes under the sublethal concentration of RMF in the treatment group and the blank control group were observed by hematoxylin-eosin(HE) staining and acridine orange(AO) staining. Meanwhile, the activities of alanine aminotransferase(ALT) and aspartate aminotransferase(AST) were determined to confirm the hepatotoxicity of RMF. Real-time quantitative polymerase chain reaction(real-time PCR) and Western blot were used to determine the expressions of genes and proteins in zebrafish larvae. Gas chromatography time-of-flight mass spectrometry(GC-TOF-MS) was used to conduct untargeted metabolomics testing to explore the mechanism. The results showed that the toxicity of RMF to zebrafish larvae was dose-dependent, with 1 100 μg·mL~(-1) of the absolute lethal concentration and 448 μg·mL~(-1) of sublethal concentration. The hepatocyte apoptosis and degeneration appeared in the zebrafish larvae under the sublethal concentration of RMF. The content of ALT and AST in zebrafish larvae at the end of the experiment was significantly increased in a dose-dependent manner. Under the sublethal concentration, the expressions of genes and proteins related to apoptosis in zebrafish larvae were significantly increased as compared with the blank control group. The results of untargeted metabolomics showed that the important metabolites related to the he-patotoxicity of RMF were mainly enriched in alanine, aspartic acid, glutamic acid, and other pathways. In conclusion, it is inferred that RMF has certain hepatotoxicity to zebrafish larvae, and its mechanism may be related to apoptosis.

Compound Characterization of a Mucuna Seed Extract: L-Dopa, Arginine, Stizolamine, and Some Fructooligosaccharides

Human societies demand sustainable alternatives for goods and services. Plants are sustainable sources of important metabolites with beneficial impacts on human health. There are many reported methodologies and commercial suppliers for extract preparations from Mucuna sp. They usually claim the plant is enriched with L-dopa, its distinctive metabolite. However, many present poor characterizations of the extract’s components. Here, we present polar metabolites characterization of a Mucuna seed extract, emphasizing L-dopa identification and quantification. To obtain the extracts, we follow a green and sustainable extraction protocol. The lyophilized extract is subjected to liquid chromatography and mass spectrometry to identify its primary metabolites. Additionally, we follow thin-layer chromatography to identify carbohydrates in the sample. The resultant extract has 56% L-dopa. Other main components in the extract are arginine, stizolamine, and the fructooligosaccharides sucrose and nystose. The characterized Mucuna extract can be easily standardized using powder preparation and used in several biomedical applications.

Characterization of the Gut Microbiota of Mackerel Icefish, Champsocephalus gunnari

The gut microbiome of Antarctic fish species has rarely been studied due to difficulties in obtaining samples. The mackerel icefish, Champsocephalus gunnari, primary feeds on krill and is one of the key species in the food web of the Southern Ocean. In this study, we characterized the gut microbiota of C. gunnari by sequencing the V3–V4 region of the bacterial 16S rRNA gene based on the Illumina MiSeq sequencing platform. We collected three types of samples: (1) whole intestine, (2) intestinal wall, and (3) intestinal content. The results showed no significant difference in the alpha diversity between different sample types. However, the microbial community composition of intestinal wall samples was distinct from other sample types. The relative abundance of Photobacterium was higher in intestinal content compared with the walls, which could be due to their chitinolytic activity. In contrast, potential pathogens such as Escherichia, Shigella, and Pseudomonas relatively more abundant in the intestinal wall compared with the intestinal contents. Unlike the gut microbiome of other marine fish species, Vibrio and Lactobacillus were nearly absent in the gut microbiome of C. gunnari. Functional gene profile of the gut microbiome predicted by PICRUSt2 showed higher relative abundance of genes related to biodegradation of nutrients in intestinal content. In contrast, the relative abundance of genes related to biosynthesis of important metabolites, such as menaquinols, was higher in intestinal wall. The difference in the microbial community structure of intestinal wall and intestinal content found in our study supports niche separation in the gut environment and emphasizes the importance of collecting intestinal wall samples in addition to intestinal content samples to understand the full picture of gut microbiome. This is the first time that the gut microbiome of mackerel icefish has been characterized using next-generation sequencing.