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Indeed, as John Cryan, a professor of anatomy and neuroscience at University College Cork, rather strikingly put it in a TEDx talk: “When you go to the bathroom and shed some of these microbes, just think: you are becoming more human……Story continues…
By: Miriam Frankel and Matt Warren
Source: How gut bacteria are controlling your brain – BBC Future
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Critics:
The microbial composition of the gut microbiota varies across the digestive tract. In the stomach and small intestine, relatively few species of bacteria are generally present.The colon, in contrast, contains the highest microbial density of any human-associated microbial community studied so far with between 1010 and 1011 cells per gram of intestinal content. These bacteria represent between 300 and 1000 different species.
However, 99% of the bacteria come from about 30 or 40 species. As a consequence of their abundance in the intestine, bacteria also make up to 60% of the dry mass of feces. Fungi, protists, archaea, and viruses are also present in the gut flora, but less is known about their activities. Over 99% of the bacteria in the gut are anaerobes, but in the cecum, aerobic bacteria reach high densities.
It is estimated that these gut flora have around a hundred times as many genes in total as there are in the human genome. Many species in the gut have not been studied outside of their hosts because they cannot be cultured. While there are a small number of core microbial species shared by most individuals, populations of microbes can vary widely.Within an individual, their microbial populations stay fairly constant over time, with some alterations occurring due to changes in lifestyle, diet and age.
The Human Microbiome Project has set out to better describe the microbiota of the human gut and other body locations. The four dominant bacterial phyla in the human gut are Bacillota (Firmicutes), Bacteroidota, Actinomycetota, and Pseudomonadota.Most bacteria belong to the genera Bacteroides, Clostridium, Faecalibacterium, Eubacterium, Ruminococcus, Peptococcus, Peptostreptococcus, and Bifidobacterium.
Other genera, such as Escherichia and Lactobacillus, are present to a lesser extent. Species from the genus Bacteroides alone constitute about 30% of all bacteria in the gut, suggesting that this genus is especially important in the functioning of the host. Fungal genera that have been detected in the gut include Candida, Saccharomyces, Aspergillus, Penicillium, Rhodotorula, Trametes, Pleospora, Sclerotinia, Bullera, and Galactomyces, among others.
Rhodotorula is most frequently found in individuals with inflammatory bowel disease while Candida is most frequently found in individuals with hepatitis B cirrhosis and chronic hepatitis B. Archaea constitute another large class of gut flora which are important in the metabolism of the bacterial products of fermentation. Industrialization is associated with changes in the microbiota and the reduction of diversity could drive certain species to extinction; in 2018, researchers proposed a biobank repository of human microbiota.
An enterotype is a classification of living organisms based on its bacteriological ecosystem in the human gut microbiome not dictated by age, gender, body weight, or national divisions. There are indications that long-term diet influences enterotype.Three human enterotypes have been proposed, but their value has been questioned. Due to the high acidity of the stomach, most microorganisms cannot survive there.
The main bacteria of the gastric microbiota belong to five major phyla: Firmicutes, Bacteroidetes, Actinobacteria, Fusobacteriota, and Proteobacteria. The dominant genera are Prevotella, Streptococcus, Veillonella, Rothia , and Haemophilus. The interaction between the pre-existing gastric microbiota with the introduction of H. pylori may influence disease progression.When there is a presence of H. pylori it becomes the dominant of the microbiota.
The small intestine contains a trace amount of microorganisms due to the proximity and influence of the stomach. Gram-positive cocci and rod-shaped bacteria are the predominant microorganisms found in the small intestine.However, in the distal portion of the small intestine alkaline conditions support gram-negative bacteria of the Enterobacteriaceae. The bacterial flora of the small intestine aid in a wide range of intestinal functions.
The bacterial flora provide regulatory signals that enable the development and utility of the gut. Overgrowth of bacteria in the small intestine can lead to intestinal failure. In addition the large intestine contains the largest bacterial ecosystem in the human body. About 99% of the large intestine and feces flora are made up of obligate anaerobes such as Bacteroides and Bifidobacterium. Factors that disrupt the microorganism population of the large intestine include antibiotics, stress, and parasites.
Bacteria make up most of the flora in the colon and accounts for 60% of fecal nitrogen.This fact makes feces an ideal source of gut flora for any tests and experiments by extracting the nucleic acid from fecal specimens, and bacterial 16S rRNA gene sequences are generated with bacterial primers. This form of testing is also often preferable to more invasive techniques, such as biopsies.
Five phyla dominate the intestinal microbiota: Bacteroidota, Bacillota (Firmicutes), Actinomycetota, Pseudomonadota, and Verrucomicrobiota – with Bacteroidota and Bacillota constituting 90% of the composition. Somewhere between 300 and 1000 different species live in the gut, with most estimates at about 500. However, it is probable that 99% of the bacteria come from about 30 or 40 species, with Faecalibacterium prausnitzii (phylum firmicutes) being the most common species in healthy adults.
Research suggests that the relationship between gut flora and humans is not merely commensal (a non-harmful coexistence), but rather is a mutualistic, symbiotic relationship.Though people can survive with no gut flora, the microorganisms perform a host of useful functions, such as fermenting unused energy substrates, training the immune system via end products of metabolism like propionate and acetate.
Preventing growth of harmful species, regulating the development of the gut, producing vitamins for the host (such as biotin and vitamin K), and producing hormones to direct the host to store fats. Extensive modification and imbalances of the gut microbiota and its microbiome or gene collection are associated with obesity.However, in certain conditions, some species are thought to be capable of causing disease by causing infection or increasing cancer risk for the host.
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