Escherichia coli
Scientific classification
Domain: Bacteria
Phylum: Proteobacteria
Stackebrandt, E. et al., 1988 [1]

The Proteobacteria are a major group (phylum) of bacteria. They include a wide variety of pathogens, such as Escherichia, Salmonella, Vibrio, Helicobacter, and Yersinia, and many other notable genera.[2] 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".[3] 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][4]

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 world that lives only inside the cells of their hosts, usually insects.

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

Gammaproteobacteria are the largest subgroup which include Acinetobacter, Pseudomonas, Escherichia coli, Salmonella, and Serratia marcescens.

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


  • Characteristics 1
  • Taxonomy 2
  • References 3
  • External links 4


All proteobacteria are 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.


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 The alpha, beta, delta, and epsilon classes are monophyletic.[5][6][7] The genus Acidithiobacillus, part of the Gammaproteobacteria until it was transferred to Class Acidithiobacillia in 2013,[8] is paraphyletic to Betaproteobacteria according to multigenome alignment studies.[9]


  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.  
  2. ^ Madigan, M. and J. Martinko. (eds.) (2005). Brock Biology of Microorganisms (11th ed.). Prentice Hall.  
  3. ^ Woese, CR (1987). "Bacterial evolution". Microbiological reviews 51 (2): 221–71.  
  4. ^ "Proteobacteria". Discover Life: Tree of Life. Retrieved 2007-02-09. 
  5. ^ Noel R. Krieg, Don J. Brenner, James T. Staley (2005). Bergey's Manual of Systematic Bacteriology: The Proteobacteria. Springer.  
  6. ^ 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.  
  7. ^ 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.  .
  8. ^ 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.  
  9. ^ 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.  

External links

  • Proteobacteria information from Palaeos.
  • Proteobacteria. – J. P. Euzéby: List of Prokaryotic names with Standing in Nomenclature.