A Microbial Biorealm page on the genus Methanobrevibacter Smithii
Archaea; Euryarchaeota; Methanobacteria; Methanobacteriales; Methanobacteriaceae; Methanobrevibacter
Description and significance
Methanobrevibacter smithii is a methanogenic Euryarchaeote. It makes up 10% of all anaerobes in the colons of healthy adults, making it the dominant archaeon in the human gut ecosystem. Metagenomic studies compared gut microbial communities of genetically obese mice with lean mice and found that obese mice contain a higher representation of genes involved in polysaccharide degradation and have more archaea. Methanobrevibacter smithii affects specificity and efficiency of bacterial digestion of dietary polysaccharides, influencing the person’s calorie harvest and body fat. This suggests that Methanobrevibacter smithii may be a therapeutic target for reducing energy harvest in obese humans (3).
The sequence was released Jun 6 2007 by Washington University. The Methanobrevibacter smithii ATCC 35061 genome is 1.85 Million bp long and composed of approximately 1837 predicted genes. The chromosomes are circular (3).
Cell structure, metabolism & life cycle
The Methanobrevibacter smithii cell is identified as coccobacillus. Optimum temperature and pH for growth is 38°C and 6.9-7.4, respectively (4). Microbes in our colons encode enzymes that help digest complex dietary polysachharides and proteins. Bacterial fermentation of polysaccharides produces short chain fatty acids, other organic acids, alchohols, and gases (CO2 and H2). Methanobrevibacter smithii is a methanogen that reduces CO2 with H2 to methane. The process of methonogenesis prevents accumulation of H2 in the human gut and improves the efficiency of microbial fermentation (3).
Ecology (including pathogenesis)
Methanobrevibacter smithii is found in the human colon, which is the last part of the digestive system in most vertebrates. The pH of the colon varies between 5.5 and 7, from slightly acid to neutral (1).
Armougom et al hypothesized a possible relationship between gut microbes and obesity. Researchers isolated microbes in feces in a sample population of obese, lean, and anorexic participants. Although the average copy number of Methanobrevibacter smithii was higher in obese participants than in lean participants, it was not significantly different. Surprisingly, there was a significantly higher copy number of Methanobrevibacter smithii in the anorexic participants than in other participants. These findings suggest the development of Methanobrevibacter smithii in anorexia nervosa patients might be associated with an adaptive attempt towards optimal exploitation of the very low caloric intake. Another explanation for the increase in Methanobrevibacter smithii is that it may help offset the increase of methane producing bacteria found in those who suffer from constipation, which commonly occurs in anorexia nervosa patients (2).
1. Allred J. Function of the large intestine. 2011. Online <http://jamesallred.com/function-of-the-colon>
2. Armougom F, Henry M, Vialettes B, Raccah D, Raoult D, “Monitoring Bacterial Community of Human Gut Microbiota Reveals an Increase in Lactobacillus in Obese Patients and Methanogens in Anorexic Patients.” PLoS ONE 2002. 4(9):e7125.doi:10.1371/journal.pone.0007125
3. Samuel B.S., Hansen E.E., Manchester J.K., Coutinho P.M., Henrissat B., Fulton R., Latreille P., Kim K., Wilson R.K., Gordon J.I., “Genomic and metabolic adaptations of Methanobrevibacter smithii to the human gut.” Proc. Natl. Acad. Sci. U.S.A. 2002.104:10643-10648.
4. Miller T.L and Lin C. Description of Methanobrevibacter gottschalkii sp. nov., Methanobrevibacter thaueri sp. nov., Methanobrevibacter woesei sp. nov. and Methanobrevibacter wolinii sp. nov. International Journal of Systematic and Evolutionary Microbiology. 2002 52: 819–822