![]() It was recently reported that TCA also induces germination of certain populations of spore-forming bacteria in the intestine and expands the culturability of gut bacteria 7. The germination of Clostridioides difficile spores, the pathogen that causes diarrhea, is stimulated by a combination of nutrients and bile salts present in the gastrointestinal tract, specifically taurocholic acid (TCA) 26, 27, 28, 29. In contrast, some spore-forming bacteria including pathogens and commensals, germinate in response to BAs in the intestinal tract 7. With bactericidal activity, BAs provide selective pressure for the colonization of bile-sensitive bacteria 25. Since these BA converting enzymes are unique to certain species of bacteria, the final composition of BAs will differ depending on the composition of gastro-intestinal microbiota 24. Alternatively, 7α-epimerization results in ursodeoxycholic acid (UDCA) from CDCA 21, 22, 23. Specifically, conjugated BAs are deconjugated by the function of the bacterial bile salt hydrolase (BSH) 19, 20 and then converted to secondary BAs through 7α-dehydroxylation, resulting in deoxycholic acids (DCA) and lithocholic acid (LCA) from CA and CDCA respectively. BAs are mostly reabsorbed and recycled at the end of the small intestine, and thereafter parts of them passed through to the large intestine, after which they are processed to secondary BAs by large intestinal microbiota. In humans, there are two main BAs, cholic acid (CA) and chenodeoxycholic acid (CDCA), which are produced and secreted into the small intestine as taurine- or glycine-conjugated forms to aid lipid absorption by forming water-soluble micelles 17, 18. It is also known that spores tolerant to the outside gut environment facilitate the host-to-host transmission of bacteria through spatio-temporal means, which is not limited to pathogens, but includes commensals beneficial to health 14.īile stress is one of the stresses experienced by intestinal bacteria. The high tolerance of these spore-forming bacteria to gut environment stress such as high and low temperature, nutrient and oxygen and drug attack allows their long-term survival 7, 14, 15, 16. The phylum Firmicutes, which includes Lachnospiraceae, Ruminococcaceae and Clostridiaceae, accounts for approximately half of the gut microbial community, many of which are known as spore-forming bacteria 7, 8, 13, 14. Although several metagenomic studies shed light on these uncultured bacteria that may have avoided past culture strategies 6, a new wave of gut microbiota culturomics is decreasing the number of unclassified microbial diversity within the gut ecosystem 7, 8, 9, 10, 11, 12. More than 2,600 of 4,500 species are estimated to be uncultured and have never been isolated in the laboratory 3, 4, despite including members that are believed to play an important biological role that remains undiscovered 2, 5. The number of bacterial cells residing in the body of human is estimated to be approximately 40-trillion bacterial cells 2, consisting of several hundreds of bacterial species out of total 4,500 estimated for all human on the earth 3. The crosstalks of host-gut microbes interaction plays a crucial role in the health and disease of human being 1. This approach would advance the research on spore-forming Clostridia that contains important but difficult-to-cultured bacteria associate with host health and diseases. These results demonstrate that the culturable range of bacteria in intestine can be widened using the germination-inducing activity of BAs. ![]() Eventually, we isolated 72 bacterial species of which 61 are known and 11 novel. There were several types of bacteria associated with different sensitivity to each BA. ![]() These colonized bacteria mostly belonged to class Clostridia, mainly consisting of families Lachnospiraceae, Clostridiaceae, and Peptostreptococcaceae. It was found that conjugated-BAs, notably three glycine-conjugated BAs, glycodeoxycholic acid and glycochenodeoxycholic acid, significantly increased the number and the species variety of colonies formed on the agar plate. To test a hypothesis that other BAs also promote germination of intestinal bacteria, we attempted culture of bacteria from ethanol-treated feces by using a series of BAs. Taurocholic acid, a conjugated form of BA, has been reported to be a factor triggering germination of a wide range of spore-forming bacteria in intestine. ![]() Structurally-diversified bile acids (BAs) are involved in shaping of intestinal microbiota as well as absorption of dietary lipids. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |