Methanobrevibacter is a genus of microorganisms that are a common inhabitant of the human body. These single-celled organisms are a type of archaea, a domain of life distinct from bacteria. Methanobrevibacter smithii is the most prevalent species found in humans and is recognized as the dominant methanogen in our system. Its presence is not a recent discovery, with research spanning over four decades revealing its role in our internal ecosystem.
Defining Methanobrevibacter and Its Niche
Methanobrevibacter belongs to the archaea, which are structurally different from bacteria with unique cell walls and membranes. These microbes are obligate anaerobes, meaning they cannot survive in the presence of oxygen. This requirement confines them to oxygen-deprived environments within the human body.
The primary residence for Methanobrevibacter is the human colon and rectum, where the slow transit time and lack of oxygen create ideal living conditions. It is a widespread member of the human gut microbiota, with one analysis finding it in nearly 96% of fecal samples from healthy people. While most prominent in the gut, its reach can extend to other areas and is acquired early in life from sources like breast milk.
Metabolic Functions and Methane Production
The primary metabolic function of Methanobrevibacter is methanogenesis—the production of methane. It is a hydrogenotrophic methanogen, meaning it uses hydrogen gas (H2) as an energy source. In the gut, it consumes H2 along with carbon dioxide (CO2) or formate, which are bacterial waste products from fermenting dietary fibers. This process results in the creation of methane (CH4).
This consumption of hydrogen is a process known as interspecies hydrogen transfer. The buildup of hydrogen gas can slow down or inhibit the fermentation activity of bacteria. By efficiently removing this excess hydrogen, Methanobrevibacter allows these bacteria to break down complex carbohydrates more effectively. This enhances the overall efficiency of dietary fermentation and leads to greater energy extraction from food.
Association with Human Health and Disease
The influence of Methanobrevibacter, particularly M. smithii, on human health is complex and tied to its methane-producing activities. Methane gas can slow down intestinal transit, the time it takes for food to move through the digestive system. This effect is associated with constipation-predominant Irritable Bowel Syndrome (IBS-C), where higher levels of methane detected on breath tests often correlate with the severity of constipation.
The organism’s role in energy regulation has also drawn considerable attention, specifically concerning obesity. By increasing fermentation efficiency, M. smithii may increase the number of calories extracted from the diet. Some studies suggest a link between the presence of methanogens and higher body weight, though this connection is not consistently found across all studies. Higher quantities of M. smithii have been observed in individuals with anorexia, possibly as an adaptation to maximize energy extraction from a low-calorie diet.
Factors Influencing Methanobrevibacter Abundance
The amount of Methanobrevibacter in the gut is not static and can be influenced by several factors, most notably diet. Because these archaea feed on fermentation byproducts, a diet rich in complex carbohydrates can provide the necessary substrates, like hydrogen and formate, to support a larger population. The specific types of fiber consumed can shape the microbial community and, in turn, affect methanogen levels.
Beyond diet, other elements can play a part in determining Methanobrevibacter abundance. The composition of the gut microbiome changes with age, and methanogen levels tend to increase as individuals get older. The initial colonization during infancy, geographic location, and host genetics are also thought to contribute to the variations seen between individuals.