Methanobrevibacter+smithii

=**//Methanobrevibacter smithii//**=



Domain: Archaea Kingdom: Archaea Phylum: Euryarchaeota Class: Methanobacteria Order: Methanobacteriales Family: Methanobacteriaceae Genus: Methanobrevibacter Species: M. smithii

**BACKGROUND**
M. smithii is nonpathogenic. Rather, M. smithii in the animal and human body (specifically the colon) have a mutual symbiotic relationship. M. smithii thrives in the colon, comprising about 10% of the anaerobic microbes there. This archaeon possesses an important role in managing bacterial waste in the human gut ecosystem as it metabolizes the end-products of bacteria fermentation into methane (1). As end-products carbon dioxide (CO2), hydrogen gas (H2), and formate are eliminated via M. smithii methanogenesis, this facilitates the activity other gut bacteria by preventing waste accumulation. Removal waste products keeps a stable pH range for the microbes which facilitates digestion of polysaccharides and complex sugars (2). M. smithii is thought to be the therapeutic target, that which its concentration is adapted for optimum health; the values highly above or much lower than 10% of all anaerobes in a healthy adult colon are considered out of optimum health range.



In total, M. smithii performs three metabolic pathways: methanogenesis from CO2, H2, formate, and alcohols, carbon assimilation from acetate and bicarbonate, and nitrogen assimilation from ammonia (10).

**//M. smithii// MICROBIAL CHARACTERISTICS**
M. smithii is a gram-positive methanogen archaeon. As a methanogen, it produces methane as a byproduct of metabolism (6). Because M. smithii exists in the human body, it is mesophilic, thriving at an optimum temperature of 38 degrees celsius; optimum pH range for this microbe is between a pH of 6.9 to 7.4 (3).

M. smithii is equipped to live and thrive in the human gut because of three characteristics: it produces surface glycans which mimic cells found in the mucosa, it has regulated gene expression for adhesion-like proteins, and it is an effective competitor for nitrogenous nutrient pools (2). As you can see in the figure below, the capsule of M. smithii compared between M. smithii recovered from the cecum, and the smaller inset M. smithii is derived from a batch fermentor. The large capsule of the M. smithii recovered from the cecum has a much larger outer capsule, which mimics the host glycan landscape.

**FUN FACTS**
//ANOREXIA & OBESITY// Based on the affects and specificity M. smithii has on polysaccharide digestion and thus its influence on host caloric harvest and adiposity, a study in 2009 revealed that there were higher proportions of M. smithii methanogens in anorexic individuals than individuals who are lean or obese (4). This may be due to adaptation to exploit a low caloric intake. In comparison, a low level of M. smithii in the gut microbiota was correlated with obesity (8).

//CONSTIPATION// A 2012 study observed an overwhelming population of those suffering from constipation-predominant irritable bowel syndrome (C-IBS) showed be methane breath producers. They concluded from studying patients with C-IBS that the number and proportion of M. smithii in their stool correlated with the amount of methane in their breath.

//FLATULENCE// M. smithii is the microbe responsible for methane production in the animal colon. This active compound is thus found in human flatulence, the active compound which makes it flammable depending on its concentration of methane (9). Methane as a gas is flammable within a range of concentrations between 4.4 - 17% in air of standard pressure (5). Thus, as seen in pop culture, lighting farts on fire is indeed possible because of archaeon M. smithii.

GLOBAL WARMING Methane in the earth's atmosphere is a large contributor (25 times greater than carbon dioxide) to the greenhouse effect and thus global warming (10). Controversy has stirred on the fact that methanogenesis in the decay of organic material and in livestock flatulence is a considerable contributor to the global warming effect.