• Journal of Microbiology and Biotechnology
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• v.30 no.9
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• pp.1367-1378
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• 2020

The polyphagous eri silk moth, Samia ricini, is associated with various symbiotic gut bacteria believed to provide several benefits to the host. The larvae of S. ricini were subjected to isolation of gut bacteria using culture-dependent 16S rRNA generic characterization, metagenomics analysis and qualitative enzymatic assays. Sixty culturable aerobic gut bacterial isolates comprising Firmicutes (54%) and Proteobacteria (46%); and twelve culturable facultative anaerobic bacteria comprising Proteobacteria (92%) and Firmicutes (8%) were identified inhabiting the gut of S. ricini. The results of metagenomics analysis revealed the presence of a diverse community of both culturable and un-culturable gut bacteria belonging to Proteobacteria (60%) and Firmicutes (20%) associated with seven orders. An analysis of the results of culturable isolation indicates that these bacterial isolates inhabited all the three compartments of the gut. Investigation on persistence of bacteria coupled with metagenomics analysis of the fifth instar suggested that bacteria persist in the gut across the different instar stages. In addition, enzymatic assays indicated that 48 and 75% of culturable aerobic, and 75% of anaerobic gut bacterial isolates had cellulolytic, lipolytic and nitrate reductase activities, thus suggesting that they may be involved in food digestion and nutritional provision to the host. These bacterial isolates may be good sources for profiling novel genes and biomolecules for biotechnological application.

• Asian-Australasian Journal of Animal Sciences
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• v.17 no.6
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• pp.877-884
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• 2004

Although gut microbial functions have been analyzed through cultivation of isolated microbes, molecular analysis without cultivation is becoming a popular approach in recent years. Gene cloning studies have partially revealed the mechanisms involved in fiber digestion of individual microbe. The molecular approach finally made it possible to analyze full genomes of the representative rumen cellulolytic bacteria Fibrobacter and Ruminococcus. The coming database may contain useful information such as regulation of gene expression relating to fiber digestion. Meanwhile, unculturable bacteria are still poorly characterized, even though they are main constituents of gut microbial ecosystem. The molecular analysis is essential to initiating the studies on these unculturable bacteria. The studies dealing with rumen and large intestine are revealing considerable complexity of the microbial ecosystems with many undescribed bacteria. These bacteria are being highlighted as possibly functional members contributing to feed digestion. Manipulation of gut bacteria and gut ecology for improving animal production is still at challenging stage. Bacteria newly introduced in the rumen, whether they are genetically modified or not, suffer from poor survival. In one of these attempts, Butyrivibrio fibrisolvens expressing a foreign dehalogenase was successfully established in sheep rumen to prevent fluoroacetate poisoning. This expands choice of forages in tropics, since many tropic plants are known to contain the toxic fluoroacetate. This example may promise the possible application of molecular breeding of gut bacteria to the host animals with significance in their health and nutrition. When inoculation strategies for such foreign bacteria are considered, it is obvious that we should have more detailed information of the gut microbial ecology.

• Food Science and Industry
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• v.52 no.3
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• pp.208-219
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• 2019

Probiotics are very closely related to gut microbiome and recognized as beneficial microorganisms for our health. They have various biological effects such as inhibition of pathogenic bacteria, activation of beneficial bacteria, prevention of diarrhea and constipation, enhanced immune activity etc. Prebiotics, non-digestible carbohydrates such as galactooligosaccharide and fructooligosaccharide, are utilized by beneficial gut bacteria such as bifidobacteria and lactobacilli, resulting in production of short chain fatty acids which inhibit pathogenic bacteria in the gut and function for human health. Synbiotics are introduced for synergistic effects when probiotics are combined with prebiotics and now commercially available. At the moment many functional ingredients are developed and commercialized. Probiotics, prebiotics, and synbiotics might be hot items in the functional food market and the values will increase according to the results of human gut microbiome researches. To meet the situation, systematic and scientific studies as well as marketing effects should be accompanied.

• Biomolecules & Therapeutics
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• v.19 no.2
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• pp.155-173
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• 2011

Humans have and hold 100 trillion intestinal bacteria that are essential for health. For millions of years human-microorganisms interaction has co-evolved, and maintained close symbiotic relationship. Gut bacteria contributes to human health and metabolism, and humans provides the optimum nutrition-rich environment for bacteria. What is the mechanism of the host distinguishing the intestinal bacteria as its cohabiting partner and what kind of benefits does the gut microbiota provide the human are the fundamental questions to be asked and solved in order to make human life a higher quality. This review explains the physiological relationship and mutualism between the host and gut microorganism, and highlights the potential therapeutic approach for treating diseases, maintaining and improving health based on these correlations.

• Molecules and Cells
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• v.44 no.5
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• pp.356-362
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• 2021

An increasing number of studies have revealed an interaction between gut microbiota and tumors. The enrichment of specific bacteria strains in the intestines has been found to modulate tumor growth and influence the mechanisms of tumor treatment. Various bacteria are involved in modulating the effects of chemotherapeutic drugs currently used to treat patients with cancer, and they affect not only gastrointestinal tract tumors but also distant organ tumors. In addition, changes in the gut microbiota are known to be involved in the antitumor immune response as well as the modulation of the intestinal immune system. As a result, the gut microbiota plays an important role in modulating the efficacy of immune checkpoint inhibitors. Therefore, gut microbiota could be considered as an adjuvant treatment option with other cancer treatment or as another marker for predicting treatment response. In this review, we examine how gut microbiota affects cancer treatments.

• Journal of Microbiology and Biotechnology
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• v.29 no.12
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• pp.1904-1915
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• 2019

Resistant starch (RS) is metabolized by gut microbiota and involved in the production of short-chain fatty acids, which are related to a variety of physiological and health effects. Therefore, the availability of RS as a prebiotic is a topic of interest, and research on gut bacteria that can decompose RS is also important. The objectives in this study were 1) to isolate a human gut bacterium having strong degradation activity on non-gelatinized RS, 2) to characterize its RS-degrading characteristics, and 3) to investigate its probiotic effects, including a growth stimulation effect on other gut bacteria and an immunomodulatory effect. Bifidobacterium adolescentis P2P3 showing very strong RS granule utilization activity was isolated. It can attach to RS granules and form them into clusters. It also utilizes high-amylose corn starch granules up to 63.3%, and efficiently decomposes other various types of commercial RS without gelatinization. In a coculture experiment, Bacteroides thetaiotaomicron ATCC 29148, isolated from human feces, was able to grow using carbon sources generated from RS granules by B. adolescentis P2P3. In addition, B. adolescentis P2P3 demonstrated the ability to stimulate secretion of Th1 type cytokines from mouse macrophages in vitro that was not shown in other B. adolescentis. These results suggested that B. adolescentis P2P3 is a useful probiotic candidate, having immunomodulatory activity as well as the ability to feed other gut bacteria using RS as a prebiotic.

• Korean Journal of Poultry Science
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• v.38 no.2
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• pp.155-164
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• 2011

The use of antimicrobials will be soon removed due to an increase of occurrence of antibiotic-resistant bacteria or ionophore-resistant Eimeria species in poultry farms and consumers' preference on drug-free chicken meats or eggs. Although dietary antimicrobials contributed to the growth and health of the chickens, we do not fully understand their interrelationship among antimicrobials, gut microbiota, and host immunity in poultry. In this review, we explored the current understanding on the effects of antimicrobials on gut microbiota and immune systems of chickens. Based on the published literatures, it is clear that antibiotics and antibiotic ionophores, when used singly or in combination could influence gut microbiota. However, antimicrobial effect on gut microbiota varied depending on the samples (e.g., gut locations, digesta vs. mucosa) used and among the experiments. It was noted that the digesta vs. the mucosa is the preferred sample with the results of no change, increase, or decrease in gut microbiota community. In future, the mucosa-associated bacteria should be targeted as they are known to closely interact with the host immune system and pathogen control. Although limited, dietary antimicrobials are known to modulate humoral and cell-mediated immunities. Ironically, the evidence is increasing that dietary antimicrobials may play an important role in triggering enteric disease such as gangrenous dermatitis, a devastating disease in poultry industry. Future work should be done to unravel our understanding on the complex interaction of host-pathogen-microbiota-antimicrobials in poultry.

• Journal of Digestive Cancer Research
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• v.10 no.1
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• pp.31-38
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• 2022

Ulcerative colitis (UC) exhibits chronic intestinal inflammatory conditions with cycles of relapse and remission. The incidence is rapidly growing in Asian countries including South Korea possibly due to changes in lifestyles. Although the etiology of inflammatory bowel disease is inconclusive, gut microbiota composition is considered a critical factor involved in the pathogenesis of UC. The overgrowth of pathogenic bacteria evokes hyper-immune responses in gut epithelium causing tissue inflammation and damage. Also, failure to regulate gut epithelium integrity due to chronic inflammation and mucus depletion accelerates bacterial translocation aggravating immune dysregulation. Gut microbiota composition responds to the diet in a very rapid manner. Epidemiological studies have indicated that the risk of UC is associated with low plant foods/high animal foods consumption. Several bacterial strains consistently found depleted in UC patients use plant food-originated dietary fiber producing short chain fatty acids to maintain epithelial integrity. These bacteria also use mucus layer mucin to keep gut microbiota diversity. These studies partly explain the association between dietary modification of gut microbiota in UC development. Further human intervention trials are required to allow the use of specific bacterial strains in the management of UC.

• Fisheries and Aquatic Sciences
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• v.11 no.2
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• pp.76-81
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• 2008

We isolated 1,916 strains of bacteria from gut and feces of abalone. The most active agarolytic bacterium, DAG-130, was identified from the gut of the abalone Haliotis gigantea. Of the bacteria harbored by both H. discus hannai and H. gigantea, 59% were agarolytic. There was no significant difference in the number of agarolytic bacteria isolated from abalone fed on the seaweeds Gelidium amansii, Laminaria japonica, or Undaria pinnatifida. Of the agarolytic bacteria, 72% were isolated from the guts of all sources tested while 43% came from the feces. The strain DAG-130 showed 100% identity with the bacterium Vibrio cyclotrophicus based on phylogenetic analysis of l6S rDNA. The bacterium produced monomers and oligomers from the agar substrate.

• Journal of Species Research
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• v.10 no.1
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• pp.1-11
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• 2021

Evidence highlighting the importance of gut microbiota in biodiversity conservation is growing; however, gut bacteria in South Korean wildlife have not been well identified. Using a culture-dependent isolation method, we identified the gut bacteria from Korean aquatic wildlife: the gazami crab (Portunus trituberculatus), Korean striped bitterling (Acheilognathus yamatsutae), oily bitterling (Acheilognathus koreensis), leopard mandarin fish (Siniperca scherzeri), Korean dark chub (Zacco koreanus), diving beetle (Cybister lewisianus), spotted steed (Abbottina springeri), and Korean spotted sleeper (Odontobutis obscura interrupta). We identified 18 strains previously unrecorded in South Korea by comparing 16S rRNA gene sequences of isolates against the EzBioCloud and National Institute of Biological Resources(NIBR) databases. The isolated strains belong to the phyla Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria. We also assessed for phylogenetic relatedness, Gram-stain reaction, colony and cell morphology, and biochemical characteristics. Basic information and 16S rRNA gene sequences of the isolates were registered in NIBR, and NIBR accession numbers are provided.