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EscherichiaColi NIAID.jpg
Escherichia coli
Scientific classification
Domain: Bacteria
Phylum: Proteobacteria
Stackebrandt et al., 1988,[1] Garrity et al. 2005[2]

The Proteobacteria are a major group (phylum) of Gram-negative bacteria. They include a wide variety of pathogens, such as Escherichia, Salmonella, Vibrio, Helicobacter, Yersinia, and many other notable genera.[3] Others are free-living (nonparasitic), and include many of the bacteria responsible for nitrogen fixation.

Carl Woese established this grouping in 1987, calling it informally the "purple bacteria and their relatives".[4] Because of the great diversity of forms found in this group, the Proteobacteria are named after Proteus, a Greek god of the sea capable of assuming many different shapes; it is not named after the genus Proteus.[1][5]

Alphaproteobacteria grow at very low levels of nutrients and have unusual morphology such as stalks and buds. They include agriculturally important bacteria capable of inducing nitrogen fixation in symbiosis with plants. An example of Alphaproteobacteria is Wolbachia, which is the most common infectious bacterial genus in the world that lives only inside the cells of their hosts, usually insects.

Betaproteobacteria often use nutrient substances that diffuse away from areas of anaerobic decomposition of organic matter (hydrogen gas, ammonia, methane) and includes chemoautotrophs. An example of Betaproteobacteria is Bordetella pertussis, which causes pertussis (whooping cough).

Gammaproteobacteria are the largest subgroup which includes Acinetobacter, Pseudomonas, Escherichia, Salmonella, and Serratia species.

Deltaproteobacteria include bacteria that are predators on other bacteria and are important contributors to the sulfur cycle. An example is Desulfovibrio, which is found in anaerobic sediments and in the intestinal tracts of humans and animals.

Epsilonproteobacteria are slender, Gram-negative rods that are helical or curved. They are also motile by flagella and are microaerophilic. An example is Helicobacter, which has been identified as the most common cause of peptic ulcers in humans and a cause of stomach cancer.


All proteobacteria are Gram-negative, with an outer membrane mainly composed of lipopolysaccharides. Many move about using flagella, but some are nonmotile or rely on bacterial gliding. The last include the myxobacteria, a unique group of bacteria that can aggregate to form multicellular fruiting bodies. Also, a wide variety in the types of metabolism exists. Most members are facultatively or obligately anaerobic, chemoautotrophs, and heterotrophic, but numerous exceptions occur. A variety of genera, which are not closely related to each other, convert energy from light through photosynthesis. These are called purple bacteria, referring to their mostly reddish pigmentation.

Proteobacteria are associated with the imbalance of microbiota of the lower reproductive tract of women. These species are associated with inflammation.[6]


Phylogeny of Proteobacteria








Phylogeny of proteobacteria according to ARB living tree, iTOL, Bergey's and others

The group is defined primarily in terms of ribosomal RNA (rRNA) sequences. The Proteobacteria are divided into six sections, referred to by the Greek letters alpha through zeta. These were previously regarded as subclasses of the phylum, but they are now treated as classes. The alpha, beta, delta, and epsilon classes are monophyletic.[7][8][9] The genus Acidithiobacillus, part of the Gammaproteobacteria until it was transferred to Class Acidithiobacillia in 2013,[10] is paraphyletic to Betaproteobacteria according to multigenome alignment studies.[11]

Proteobacterial clades include some prominent genera,[12] e.g.:


  1. ^ a b Stackebrandt, E.; Murray, R. G. E.; Truper, H. G. (1988). "Proteobacteria classis nov., a Name for the Phylogenetic Taxon That Includes the "Purple Bacteria and Their Relatives"". International Journal of Systematic Bacteriology. 38 (3): 321–325. doi:10.1099/00207713-38-3-321. 
  2. ^ Garrity, G. M., Bell, J. A. & Lilburn, T. (2005). Phylum XIV. Proteobacteria phyl. nov. In: Bergey’s Manual of Systematic Bacteriology, 2nd edn, vol. 2 (The Proteobacteria), part B (The Gammaproteobacteria), p. 1. Edited by D. J. Brenner, N. R. Krieg, J. T. Staley & G. M. Garrity. New York: Springer.
  3. ^ Madigan, M. and J. Martinko. (eds.) (2005). Brock Biology of Microorganisms (11th ed.). Prentice Hall. ISBN 0-13-144329-1. 
  4. ^ Woese, CR (1987). "Bacterial evolution". Microbiological reviews. 51 (2): 221–71. PMC 373105free to read. PMID 2439888. 
  5. ^ "Proteobacteria". Discover Life: Tree of Life. Retrieved 2007-02-09. 
  6. ^ Bennett, John (2015). Mandell, Douglas, and Bennett's principles and practice of infectious diseases. Philadelphia, PA: Elsevier/Saunders. ISBN 9781455748013; Access provided by the University of Pittsburgh 
  7. ^ Noel R. Krieg; Don J. Brenner; James T. Staley (2005). Bergey's Manual of Systematic Bacteriology: The Proteobacteria. Springer. ISBN 978-0-387-95040-2. 
  8. ^ Ciccarelli, FD; Doerks, T; Von Mering, C; Creevey, CJ; Snel, B; Bork, P (2006). "Toward automatic reconstruction of a highly resolved tree of life". Science. 311 (5765): 1283–7. doi:10.1126/science.1123061. PMID 16513982. 
  9. ^ Yarza, P; Ludwig, W; Euzéby, J; Amann, R; Schleifer, KH; Glöckner, FO; Rosselló-Móra, R (2010). "Update of the All-Species Living Tree Project based on 16S and 23S rRNA sequence analyses". Systematic and Applied Microbiology. 33 (6): 291–9. doi:10.1016/j.syapm.2010.08.001. PMID 20817437. .
  10. ^ Williams, KP; Kelly, DP (2013). "Proposal for a new class within the phylum Proteobacteria, Acidithiobacillia classis nov., with the type order Acidithiobacillales, and emended description of the class Gammaproteobacteria". International Journal of Systematic and Evolutionary Microbiology. 63 (Pt 8): 2901–6. doi:10.1099/ijs.0.049270-0. PMID 23334881. 
  11. ^ Williams, K. P.; Gillespie, J. J.; Sobral, B. W. S.; Nordberg, E. K.; Snyder, E. E.; Shallom, J. M.; Dickerman, A. W. (2010). "Phylogeny of Gammaproteobacteria". Journal of Bacteriology. 192 (9): 2305–14. doi:10.1128/JB.01480-09. PMC 2863478free to read. PMID 20207755. 
  12. ^ Interactive Tree of Life

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