In terms of diversity and sheer numbers, the microbes occupying the human gut easily dwarf the billions of people inhabiting the Earth. Numbering in the tens of trillions and representing many thousands of distinct genetic families, this microbiome, as it's called, helps the body perform a variety of regulatory and digestive functions, many still poorly understood.
A collaboration aimed at uncovering the links between the microbial composition of the human gut and morbid obesity began when Dr. John DiBaise, a gastroenterologist at the Mayo Clinic, Arizona, became interested in both the underlying mechanisms of obesity and plausible alternatives to gastric bypass surgery—still the only reliable long-term treatment for the extremely overweight.
DiBaise turned to Bruce Rittmann, Ph.D., an environmental engineer and a member of National Academy of Engineering, whose Center for Environmental Biotechnology uses its expertise to examine microbial populations important for cleaning up pollutants and generating renewable bioenergy. Rittmann invited Rosa Krajmalnik-Brown, assistant professor of civil and environmental engineering, to collaborate and apply her microbial ecology expertise to this project. The three researchers were able to leverage seed funding from the Mayo Clinic and ASU so that they could combine their respective talents. DiBaise recruited 9 middle-aged volunteers in three groups—normal weight, morbidly obese and following gastric bypass surgery—to participate in the study.
The research team's central hypothesis is that differing microbial populations in the gut allow the body to harvest more energy, making people more susceptible to developing obesity. These small differences can, over time, profoundly affect an individual's weight. Supporting this view is the study's confirmation that the microbial composition among obese patients appears significantly altered compared with both normal weight individuals and those who have undergone gastric bypass surgery.
A microbial managerie
To tease out the microbial human gut composition, Husen Zhang, a postdoctoral scholar working with Rittmann and Krajmalnik-Brown, used an advanced DNA sequencing technology and sophisticated ecological tools. The team examined 184,094 gene sequences of microbial 16S rRNA, a molecular structure which provides a characteristic fingerprint for microbial identification. The analysis was conducted with the assistance of University of Arizona's Rod Wing at the Bio5 Institute, using a novel sequencing technique known as 454-pyrosequencing, which allows a significantly larger number and greater diversity of gut microbia to be identified.
The group's latest findings represent the first investigation of gut microbiota from post-gastric-bypass patients to date.
By examining a specific region of the 16S rRNA gene known as V6—PCR amplified from the stool samples of the 9 test subjects—the researchers were able to classify a zoo of microorganisms, which fell into 6 broad categories, with two bacterial phyla, the bacteroidetes and firmicutes, predominanting.
The resulting composition of gut microbiota in the three gastric bypass patients differed substantially and in potentially important ways from obese and normal weight individuals. This means the drastic anatomical changes created by gastric bypass surgery appear to have profound effects on the microorganisms that inhabit the intestine. This change may be part of the reason that gastric-bypass surgery is the most effective means to treat obesity today.
The team's study is the first molecular survey of gut microbial diversity following surgical weight loss, and has helped solidify the link between methane producing microbes and obesity. Specifically, the microbial populations extracted from obese individuals were high in a particular microbial subgroup, hydrogen-producing bacteria known as prevotellaceae. Further, such hydrogen producers appear to coexist with hydrogen-consuming methanogens, found in abundance in obese patients, but absent in both normal weight and gastric bypass samples. Unlike the hydrogen producers, however, these methane-liberating hydrogen consumers are not bacteria. They belong instead to the third great microbial domain—the Archaea, (with Eukarya and Bacteria making up the other two).
During the course of digestion, calories are extracted from food and stored in fat tissue for later use—a process delicately regulated by the multitude of microbial custodians. The intermediary products of the digestive process include hydrogen, carbon dioxide and several short chain fatty acids (SCFAs).
Results suggest a cooperative co-existence in obese individuals between hydrogen-producers and hydrogen consuming methanogens. Rittmann explains how this mutually reinforcing relationship, known as syntrophy, may contribute to obesity:
"Organisms producing hydrogen and acetate create a situation like cars flooding onto the highway. The methanogens, which remove the hydrogen, are like the offramps, allowing the hydrogen cars to get off. That allows more acetate cars to get on, because some hydrogen cars are coming off the highway."
The methanogen offramps, by removing hydrogen, accelerate the efficient fermentation of otherwise indigestible plant polysaccharides and carbohydrates. The effect is to boost production of SCFAs, particularly acetate, which will be taken up by the intestinal epithelium and converted to fat. The result over time may be increasing weight, eventually leading to obesity.
While weight regulation involves a complex interplay of genetic predisposition, exercise, eating habits, and other factors, manipulation of the gut's microflora, particularly the methanogenic Archaea, may provide additional avenues for the treatment of morbid obesity.
The researchers stress that the study is preliminary, but were encouraged by the findings from their small sample. Future investigation is needed to establish the differences in composition of gut microbiota across different age groups and under varying weight-loss regimens involving diet and exercise. Nevertheless, the study's findings point to new avenues for modifying the body's energy harvesting efficiency—perhaps by manipulation of the Bacteria-Archaea nexus.
Joe Caspermeyer | EurekAlert!
Further reports about: > Bacteria-Archaea nexus > DiBaise > Microbiome > SCFAs > bacterial phyla > body weight differences > digestive functions > distinct genetic families > gastric bypass > gastric bypass surgery > hydrogen-consuming methanogens > methane-liberating hydrogen > microbial communities > microbial ecology > microbial managerie > microbial mélange > microbial population > molecular structure > morbid obesity > normal weight individuals > sophisticated ecological tools
WAKE-UP provides new treatment option for stroke patients | International study led by UKE
17.05.2018 | Universitätsklinikum Hamburg-Eppendorf
First form of therapy for childhood dementia CLN2 developed
25.04.2018 | Universitätsklinikum Hamburg-Eppendorf
A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.
The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
The historic first detection of gravitational waves from colliding black holes far outside our galaxy opened a new window to understanding the universe. A...
02.05.2018 | Event News
13.04.2018 | Event News
12.04.2018 | Event News
24.05.2018 | Ecology, The Environment and Conservation
24.05.2018 | Medical Engineering
24.05.2018 | Physics and Astronomy