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EscherichiaColi NIAID.jpg
Escherichia coli cells magnified 25,000 times
Scientific classification
Domain: Bacteria
(unranked): Gracilicutes
Gibbons and Murray 1978[1]


Gracilicutes (Latin: gracilis, slender, and cutis, skin, referring to the cell wall) is a controversial taxon in bacterial taxonomy.

Traditionally gram staining results were most commonly used as a classification tool, consequently until the advent of molecular phylogeny, the Kingdom Monera (as the domains Bacteria and Archaea were known then) was divided into four phyla,[2][3]

This classification system was abandoned in favour of the three-domain system based on molecular phylogeny started by C. Woese.[5][6]

This taxon was revived in 2006 by Cavalier-Smith as an infrakindgom containing the phyla Spirochaetae, Sphingobacteria, Planctobacteria, and Proteobacteria.[7] However, this taxon is not generally accepted and the three-domain system is followed.[8]

It is a gram-negative clade that branched off from other bacteria just before the evolutionary loss of the outer membrane or capsule, and just after the evolution of flagella.[7]


The following graph shows Cavalier-Smith's version of the tree of life, indicating the status of Gracilicutes.[9]


  1. ^ Gibbons, N. E. & Murray, R. G. E. 1978. Proposals concerning the higher taxa of bacteria. Int J Syst Bacteriol 28:1–6, (PDF)
  2. ^ Gibbons, N.E. & Murray, R.G.E. (1978). Proposals concerning the higher taxa of bacteria. International Journal of Systematic Bacteriology, 28, 1-6, [1].
  3. ^ Krieg, N.R. & Holt, J.C. (eds., 1984). Bergey’s Manual of Systematic Bacteriology, 1st ed., vol. 1, Williams and Wilkins, Baltimore, [2].
  4. ^ Murray, R.G.E. (1984). The higher taxa, or, a place for everything...?. In: N.R. Krieg & J.G. Holt (ed.) Bergey's Manual of Systematic Bacteriology, vol. 1, The Williams & Wilkins Co., Baltimore, p. 31-34
  5. ^ Woese, C. R. (1987). "Bacterial evolution". Microbiological reviews. 51 (2): 221–271. PMC 373105free to read. PMID 2439888. 
  6. ^ Don J. Brenner, Noel R. Krieg, James T. Staley (July 26, 2005) [1984(Williams & Wilkins)]. George M. Garrity, ed. Introductory Essays. Bergey's Manual of Systematic Bacteriology. 2A (2nd ed.). New York: Springer. p. 304. ISBN 978-0-387-24143-2. British Library no. GBA561951. 
  7. ^ a b Cavalier-Smith T (2006). "Rooting the tree of life by transition analyses". Biol. Direct. 1: 19. doi:10.1186/1745-6150-1-19. PMC 1586193free to read. PMID 16834776. 
  8. ^ Krieg, N.R.; Ludwig, W.; Whitman, W.B.; Hedlund, B.P.; Paster, B.J.; Staley, J.T.; Ward, N.; Brown, D.; Parte, A. (November 24, 2010) [1984(Williams & Wilkins)]. George M. Garrity, ed. The Bacteroidetes, Spirochaetes, Tenericutes (Mollicutes), Acidobacteria, Fibrobacteres, Fusobacteria, Dictyoglomi, Gemmatimonadetes, Lentisphaerae, Verrucomicrobia, Chlamydiae, and Planctomycetes. Bergey's Manual of Systematic Bacteriology. 4 (2nd ed.). New York: Springer. p. 908. ISBN 978-0-387-95042-6. British Library no. GBA561951. 
  9. ^ Cavalier-Smith T (2006). "Cell evolution and Earth history: stasis and revolution" (PDF). Philos Trans R Soc Lond B Biol Sci. 361 (1470): 969–1006. doi:10.1098/rstb.2006.1842. PMC 1578732free to read. PMID 16754610.