why do we have bacteria in our intestines

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The composition of our microbiota evolves throughout our entire life, from birth to old age, and is the result of different environmental influences
Gut microbiotaвs balance can be affected during the ageing process and, consequently, the elderly have substantially different microbiota to younger adults. While the general composition of the intestinal microbiota is similar in most healthy people, the species composition is highly personalised and largely determined by our environment and our diet. The composition of gut microbiota may become accustomed to dietary components, either temporarily or permanently. Japanese people, for example, can digest seaweeds (part of their daily diet) thanks to specific enzymes that their microbiota has acquired from marine bacteria. Although it can adapt to change, a loss of balance in gut microbiota may arise in some specific situations. This is called dysbiosis. Dysbiosis may be linked to health problems such as functional bowel disorders, inflammatory bowel disease, allergies, obesity and diabetes. Many studies have demonstrated the beneficial effects of prebiotics and probiotics on our gut microbiota. Serving as вfood\” for beneficial bacteria, prebiotics help improve the functioning of microbiota while allowing the growth and activity of some вgood\” bacteria.

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Present in some fermented products such as yoghourt, probiotics help gut microbiota keep its balance, integrity and diversity. Thanks to technological progress, the picture of the bacteria living in the gastrointestinal tract is becoming clearer. Researchers now use a range of techniques, including the tools derived from molecular biology, to further clarify the mysteries of microbiota. While there are still some things that are yet to be discovered, more and more findings are being presented every day. Multiple laboratories have detected factors native to bacteria that have properties similar to peptide hormones of vertebrates. The functions of these peptides in the bacteria are not known. Likewise, it is not known whether these peptides act on other organisms (eg, microbes or vertebrates). Pastan and colleagues, using standard techniques of the day, characterized a thyrotropin-like peptide from Clostridium perfringens that resembled native pituitary thyrotropin in its ability to enhance glucose oxidation, phospholipid synthesis, and colloid droplet formation in thyroid slices. More impressive, when injected systemically into chicks, it stimulated the thyroid to release iodine into the bloodstream. On gel filtration, the thyrotropin-like peptide eluted in a region typical of a globular protein of 30 kd and it was destroyed by pronase, a broad-spectrum agent of proteolysis.

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Because proteases and lectins, for example, also are able to generate hormone-like receptor-mediated bioactivities in target cells, further studies are needed to define better the relationship of the clostridial peptide to the pituitary hormone. Studying bacteria and yeast, other groups have reported material that has biologic and immunologic characteristics resembling human chorionic gonadotropic (hCG) hormone and molecules that have binding properties that resemble those of hCG receptors. In studies of E coli grown in a simple synthetic medium, Roth and colleagues detected peptides that resemble mammalian insulin in extracts of the bacteria and in conditioned (cell-free) medium. The peptides behaved like insulin in a standard radioimmunoassay, in an in vitro adipocyte bioassay, and in several chromatographic systems. On gel filtration, the peptide eluted broadly in a region comparable to a globular peptide of approximately 8 kd. The bioactivity was blocked by anti-insulin antibody and by anti-insulin receptor antibody. , In similar studies of E coli grown in a simple synthetic medium, these researchers isolated and characterized a melanocortin-like material that corresponds in structure to the C terminus of elongation factor G, which shares some structural similarities to alpha-melanocyte-stimulating hormone (alpha-MSH) and to corticotropin. , A synthetic replicate of the E coli peptide mimics alpha-MSH in its interactions with four mammalian melanocortin receptor classes (melanocortin 5 receptor [MC5-R] not tested), therefore named MECO-1 (melanocortin from E coli ).

MECO-1 and alpha-MSH show affinity and biologic potency in vitro and in vivo that are extremely similar, despite the divergences in structure. The authors have considered the possibility that MSH-like peptides from microbes, acting on MC1-Rs on immune cells in the intestine, bolster the anti-inflammatory forces there. More speculative is the suggestion that MECO-1-like peptides, acting through MC3-R and MC4-R, may modulate feeding. More broadly, the authors have raised the suggestion that microbes of the gut, in addition to their role as a metabolic organ in the host, also may be a source of hormone-like signals to host cells. In other review articles, the authors have referred to similar peptides in unicellular eukaryotes, such as Neurospora and Candida species, and also catalogued early examples of systems in prokaryotes and eukaryotes that resemble systems in vertebrates.

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