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Previous story Manipulating gut microbes to improve human health topic of next Oregon State Science Pub Next story


Story by oregonstate.edu
Published on Sunday May 30, 2021 - 3:07 AM
 
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CORVALLIS, Oregon - The Oregon State University Science Pub on June 7 will focus on how insights from the field of restoration ecology, which was designed to heal natural ecosystems, may help health practitioners to manipulate the gut microbiome in ways that improve human health.

The virtual event will feature a talk by Matt Orr, an associate professor of biology at OSU-Cascades. His presentation is titled: "Your inner ecosystem: How to assist your gut microbes for better health."

An estimated 50% to 90% of the cells in the body are microbes. DNA sequencing technology has helped scientists to track the health effects of gut microbiota. The identity of microbes is associated with chronic diseases such as diabetes, obesity, inflammatory bowel disease and cancer. Orr's talk will be informed by efforts to restore damaged habitats in the environment. He will review the health effects of gut microbes and strategies for improving their performance.

The free Science Pub will run from 6 to 7:30 p.m. The event will be broadcast on YouTube Live. Registration is required and can be completed at https://beav.es/3gs.

Sponsors of Science Pub include the OSU Office of Research, OSU-Cascades in Bend and the Oregon Museum of Science and Industry. Connect Central Oregon, a collaborative program with the OSU-Cascades Innovation Co-Lab, will produce the event with student interns.

About Oregon State University: As one of only two land, sea, space and sun grant universities in the nation, Oregon State serves Oregon and the world by working on today's most pressing issues. Our more than 33,000 students come from across the globe, and our programs operate in every Oregon county. Oregon State receives more research funding than all of the state's comprehensive public universities combined. At our campuses in Corvallis and Bend, marine research center in Newport and award-winning Ecampus, we excel at shaping today's students into tomorrow's leaders.


Background

Gut microbiota, gut flora, or microbiome are the microorganisms including bacteria, archaea and fungi that live in the digestive tracts of humans and other animals including insects. The gastrointestinal metagenome is the aggregate of all the genomes of gut microbiota. The gut is the main location of human microbiota.

n humans, the gut microbiota has the largest numbers of bacteria and the greatest number of species compared to other areas of the body. In humans, the gut flora is established at one to two years after birth, by which time the intestinal epithelium and the intestinal mucosal barrier that it secretes have co-developed in a way that is tolerant to, and even supportive of, the gut flora and that also provides a barrier to pathogenic organisms.

The relationship between some gut flora and humans is not merely commensal , but rather a mutualistic relationship.:700 Some human gut microorganisms benefit the host by fermenting dietary fiber into short-chain fatty acids , such as acetic acid and butyric acid, which are then absorbed by the host. Intestinal bacteria also play a role in synthesizing vitamin B and vitamin K as well as metabolizing bile acids, sterols, and xenobiotics. The systemic importance of the SCFAs and other compounds they produce are like hormones and the gut flora itself appears to function like an endocrine organ, and dysregulation of the gut flora has been correlated with a host of inflammatory and autoimmune conditions.

The composition of human gut microbiota changes over time, when the diet changes, and as overall health changes. A systematic review from 2016 examined the preclinical and small human trials that have been conducted with certain commercially available strains of probiotic bacteria and identified those that had the most potential to be useful for certain central nervous system disorders. Classifications

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 recorded in any habitat on Earth with up to 1012 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 most cannot be cultured. While there are a small number of core species of microbes shared by most individuals, populations of microbes can vary widely among different individuals. Within an individual, microbe populations stay fairly constant over time, even though some alterations may occur with changes in lifestyle, diet and age. The Human Microbiome Project has set out to better describe the microflora of the human gut and other body locations.

The four dominant bacterial phyla in the human gut are Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria. 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.

Industralization 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. Enterotype

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.

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 60% of the dry mass of feces. 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: bacteroidetes, firmicutes, actinobacteria, proteobacteria, and verrucomicrobia—with bacteroidetes and firmicutes 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 being the most common species in healthy adults.

Research suggests that the relationship between gut flora and humans is not merely commensal , 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 , 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.

Diet

Studies and statistical analyses have identified the different bacterial genera in gut microbiota and their associations with nutrient intake. Gut microflora is mainly composed of three enterotypes: Prevotella, Bacteroides, and Ruminococcus. There is an association between the concentration of each microbial community and diet. For example, Prevotella is related to carbohydrates and simple sugars, while Bacteroides is associated with proteins, amino acids, and saturated fats. Specialist microbes that break down mucin survive on their host's carbohydrate excretions. One enterotype will dominate depending on the diet. Altering the diet will result in a corresponding change in the numbers of species. A 2021 study suggests that childhood diet and exercise can substantially affect adult microbiome composition and diversity. Its authors show that in mice a diet high in fat and sugar still substantially affects the gut microbiome after what equates to six human years. Vegetarian and vegan diets

While plant-based diets have some variation, vegetarian and vegan diets patterns are the most common. Vegetarian diets exclude meat products but still allow for eggs and dairy, while vegan diets exclude all forms of animal products. The diets of vegetarian and vegan individuals create a microbiome distinct from meat eaters, however there is not a significant distinction between the two. In diets that are centered around meat and animal products, there are high abundances of Alistipes, Bilophila and Bacteroides which are all bile tolerant and may promote inflammation in the gut. In this type of diet, the group Firmicutes, which is associated with the metabolism of dietary plant polysaccharides, is found in low concentrations. Conversely, diets rich in plant-based materials are associated with greater diversity in the gut microbiome overall, and have a greater abundance of Prevotella, responsible for the long-term processing of fibers, rather than the bile tolerant species. Diet can be used to alter the composition of the gut microbiome in relatively short timescales. However, if wanting to change the microbiome to combat a disease or illness, long-term changes in diet have proven to be most successful. Geography

Gut microbiome composition depends on the geographic origin of populations. Variations in a trade-off of Prevotella, the representation of the urease gene, and the representation of genes encoding glutamate synthase/degradation or other enzymes involved in amino acids degradation or vitamin biosynthesis show significant differences between populations from the US, Malawi or Amerindian origin.

The US population has a high representation of enzymes encoding the degradation of glutamine and enzymes involved in vitamin and lipoic acid biosynthesis; whereas Malawi and Amerindian populations have a high representation of enzymes encoding glutamate synthase and they also have an overrepresentation of a-amylase in their microbiomes. As the US population has a diet richer in fats than Amerindian or Malawian populations which have a corn-rich diet, the diet is probably the main determinant of the gut bacterial composition.

Further studies have indicated a large difference in the composition of microbiota between European and rural African children. The fecal bacteria of children from Florence were compared to that of children from the small rural village of Boulpon in Burkina Faso. The diet of a typical child living in this village is largely lacking in fats and animal proteins and rich in polysaccharides and plant proteins. The fecal bacteria of European children were dominated by Firmicutes and showed a marked reduction in biodiversity, while the fecal bacteria of the Boulpon children was dominated by Bacteroidetes. The increased biodiversity and different composition of gut flora in African populations may aid in the digestion of normally indigestible plant polysaccharides and also may result in a reduced incidence of non-infectious colonic diseases.

On a smaller scale, it has been shown that sharing numerous common environmental exposures in a family is a strong determinant of individual microbiome composition. This effect has no genetic influence and it is consistently observed in culturally different populations. Malnourishment

Malnourished children have less mature and less diverse gut microbiota than healthy children, and changes in the microbiome associated with nutrient scarcity can in turn be a pathophysiological cause of malnutrition. Malnourished children also typically have more potentially pathogenic gut flora, and more yeast in their mouths and throats. Altering diet may lead to changes in gut microbiota composition and diversity. Race and ethnicity

Researchers with the American Gut Project and Human Microbiome Project found that twelve microbe families varied in abundance based on the race or ethnicity of the individual. The strength of these associations is limited by the small sample size: the American Gut Project collected data from 1,375 individuals, 90% of whom were white. The Healthy Life in an Urban Setting study in Amsterdam found that those of Dutch ancestry had the highest level of gut microbiota diversity, while those of South Asian and Surinamese descent had the lowest diversity. The study results suggested that individuals of the same race or ethnicity have more similar microbiomes than individuals of different racial backgrounds.