Bacteroides thetaiotaomicron

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Bacteroides thetaiotaomicron
Scientific classification
Bacteroides thetaiotaomicron
Binomial name
Bacteroides thetaiotaomicron
(Distaso 1912) Castellani and Chalmers 1919

Bacteroides thetaiotaomicron (formerly Bacillus thetaiotaomicron) is a species of bacterium of the genus Bacteroides. It is a gram-negative obligate anaerobe. It is one of the most common bacteria found in human gut flora and is also an opportunistic pathogen. Its genome contains numerous genes apparently specialized in digestion of polysaccharides.

History and taxonomy[edit]

Bacteroides thetaiotaomicron was first described in 1912 under the name Bacillus thetaiotaomicron and moved to the genus Bacteroides in 1919.[1] It was originally isolated from adult human feces.[2] The specific name derives from the Greek letters theta, iota, and omicron; the List of Prokaryotic names with Standing in Nomenclature indicates this as "relating to the morphology of vacuolated forms".[1] The name is used as an example of an "arbitrary" species name in the International Code of Nomenclature of Prokaryotes.[3][4]


The genome of B. thetaiotaomicron was sequenced in 2003. It is 6.26 megabases in length, but has a relatively small number of distinct genes, due to many genes coding for proteins that are unusually large compared to other prokaryotes.[2] This genomic feature is shared with another member of the genus with a similar lifestyle, Bacteroides fragilis.[5] The genome is notable for containing very large numbers of genes associated with breaking down polysaccharides, including glycoside hydrolases and starch binding proteins.[2][5] The genome also contains large numbers of genes encoding proteins involved in sensing and responding to the extracellular environment, such as sigma factors and two-component systems.[2][6][7]


B. thetaiotaomicron is capable of metabolizing a very diverse range of polysaccharides. Its complement of enzymes for hydrolysis of glycosidic bonds is among the largest known in prokaryotes, and it is thought to be capable of hydrolyzing most glycosidic bonds in biological polysaccharides.[5] As a component of the human gut flora, it can use both dietary carbohydrates and those sourced from the host depending on nutrient availability.[8]

Although it is considered an obligate anaerobe, B. thetaiotaomicron is aerotolerant and can survive, but not grow, when exposed to oxygen. It expresses a number of proteins that scavenge reactive oxygen species such as hydrogen peroxide when exposed to air.[9]

Role in the human microbiome[edit]

B. thetaiotaomicron is one of the most common components of the human gut flora. In a long-term study of Bacteroides species in clinical samples, B. thetaiotaomicron was the second most common species isolated, behind Bacteroides fragilis.[10] B. thetaiotaomicron is considered commensal or symbiotic.[2][5] However, it is also an opportunistic pathogen and can infect tissues exposed to gut flora.[9] Its polysaccharide-metabolizing abilities make it a food source for other components of the microbiome. For example, while B. thetaiotaomicron expresses sialidase enzymes, it cannot catabolize sialic acid; as a result its presence increases the free sialic acid available for other organisms in the gut. These interactions can contribute to the growth of pathogenic bacteria such as Clostridium difficile, which uses sialic acid as a carbon source.[11] Similar interactions can cause B. thetaiotaomicron to exacerbate pathogenic E. coli infection.[12]


  1. ^ a b "Bacteroides". List of Prokaryotic names with Standing in Nomenclature. Retrieved 20 May 2018.
  2. ^ a b c d e Xu, J. (28 March 2003). "A Genomic View of the Human-Bacteroides thetaiotaomicron Symbiosis". Science. 299 (5615): 2074–2076. doi:10.1126/science.1080029.
  3. ^ Schink, Bernhard; Oren, Aharon; Vandamme, Peter (10 June 2016). "Notes on the use of Greek word roots in genus and species names of prokaryotes". International Journal of Systematic and Evolutionary Microbiology. 66 (6): 2129–2140. doi:10.1099/ijsem.0.001063.
  4. ^ Trüper, Hans G. (April 1999). "How to name a prokaryote?: Etymological considerations, proposals and practical advice in prokaryote nomenclature". FEMS Microbiology Reviews. 23 (2): 231–249. doi:10.1111/j.1574-6976.1999.tb00397.x.
  5. ^ a b c d Wexler, H. M. (12 October 2007). "Bacteroides: the Good, the Bad, and the Nitty-Gritty". Clinical Microbiology Reviews. 20 (4): 593–621. doi:10.1128/CMR.00008-07.
  6. ^ Xu, J (January 2004). "Message from a human gut symbiont: sensitivity is a prerequisite for sharing". Trends in Microbiology. 12 (1): 21–28. doi:10.1016/j.tim.2003.11.007.
  7. ^ Flint, Harry J.; Bayer, Edward A.; Rincon, Marco T.; Lamed, Raphael; White, Bryan A. (1 February 2008). "Polysaccharide utilization by gut bacteria: potential for new insights from genomic analysis". Nature Reviews Microbiology. 6 (2): 121–131. doi:10.1038/nrmicro1817.
  8. ^ Sonnenburg, J. L. (25 March 2005). "Glycan Foraging in Vivo by an Intestine-Adapted Bacterial Symbiont". Science. 307 (5717): 1955–1959. doi:10.1126/science.1109051.
  9. ^ a b Mishra, Surabhi; Imlay, James A. (December 2013). "An anaerobic bacterium, , uses a consortium of enzymes to scavenge hydrogen peroxide". Molecular Microbiology. 90 (6): 1356–1371. doi:10.1111/mmi.12438. PMC 3882148.
  10. ^ Snydman, David R.; Jacobus, Nilda V.; McDermott, Laura A.; Golan, Yoav; Hecht, David W.; Goldstein, Ellie J. C.; Harrell, Lizzie; Jenkins, Stephen; Newton, Duane; Pierson, Carl; Rihs, John D.; Yu, Victor L.; Venezia, Richard; Finegold, Sydney M.; Rosenblatt, Jon E.; Gorbach, Sherwood L. (January 2010). "Lessons Learned from the Anaerobe Survey: Historical Perspective and Review of the Most Recent Data (2005–2007)". Clinical Infectious Diseases. 50 (s1): S26–S33. doi:10.1086/647940.
  11. ^ Bäumler, Andreas J.; Sperandio, Vanessa (7 July 2016). "Interactions between the microbiota and pathogenic bacteria in the gut". Nature. 535 (7610): 85–93. doi:10.1038/nature18849. PMC 5114849.
  12. ^ Curtis, Meredith M.; Hu, Zeping; Klimko, Claire; Narayanan, Sanjeev; Deberardinis, Ralph; Sperandio, Vanessa (December 2014). "The Gut Commensal Bacteroides thetaiotaomicron Exacerbates Enteric Infection through Modification of the Metabolic Landscape". Cell Host & Microbe. 16 (6): 759–769. doi:10.1016/j.chom.2014.11.005.