| Gracilicutes | |
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| Escherichia coli cells magnified 25,000 times | |
Scientific classification 
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| Domain: | Bacteria |
| (unranked): | Gracilicutes Gibbons and Murray 1978[1] |
| Superphyla/Phyla | |
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Various definitions, see text | |
Gracilicutes (Latin: gracilis, slender, and cutis, skin, referring to the cell wall) is a clade in bacterial phylogeny.[2]
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,[1][3]
- Gracilicutes (gram-negative, it is split in many groups, but some authors still use it in a narrower sense)
- Firmacutes [sic] (gram-positive, subsequently corrected to Firmicutes,[4] today it excludes the Actinomycetota)
- Mollicutes (gram variable, later renamed Tenericutes and now Mycoplasmatota, e.g. Mycoplasma)
- Mendosicutes (uneven gram stain, "methanogenic bacteria" now known as methanogens and classed as Archaea)
This classification system was abandoned in favour of the three-domain system based on molecular phylogeny started by C. Woese.[5][6]
Using hand-drawn schematics rather than standard molecular phylogenetic analysis, Gracilicutes was revived in 2006 by Cavalier-Smith as an infrakindgom containing the phyla Spirochaetota, Sphingobacteria (FCB), Planctobacteria (PVC), and Proteobacteria.[7] 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] Most notably, this author assumed an unconventional tree of life placing Chloroflexota near the origin of life and Archaea as a close relative of Actinomycetota. This taxon is not generally accepted and the three-domain system is followed.[8]
A taxon called Hydrobacteria was defined in 2009 from a molecular phylogenetic analysis of core genes. It is in contrast to the other major group of eubacteria called Terrabacteria.[9] Some researchers have used the name Gracilicutes in place of Hydrobacteria, but this does not agree with the original description of Gracilicutes by Gibbons and Murray, noted above, which included cyanobacteria and did not follow the three-domain system. Also as noted above, the use of Gracilicutes by Cavalier-Smith can be rejected because it was a major alteration of an earlier taxonomic name, was not based on a statistical analysis, and did not follow the three-domain system. The most recent genomic analyses have supported the division of Bacteria into two major superphyla, corresponding to Terrabacteria and Hydrobacteria.[10][11]
- ^ a b Gibbons NE, Murray RG (January 1978). "Proposals concerning the higher taxa of bacteria". International Journal of Systematic and Evolutionary Microbiology. 28 (1): 1–6. doi:10.1099/00207713-28-1-1.
- ^ Boussau B, Guéguen L, Gouy M (October 2008). "Accounting for horizontal gene transfers explains conflicting hypotheses regarding the position of aquificales in the phylogeny of Bacteria". BMC Evolutionary Biology. 8: 272. doi:10.1186/1471-2148-8-272. PMC 2584045. PMID 18834516.
Accounting for horizontal gene transfers explains conflicting hypotheses regarding the position of Aquificales in the phylogeny of Bacteria
- ^ Krieg NR, Holt JC, eds. (1984). Bergey's Manual of Systematic Bacteriology. Vol. 1 (1st ed.). Baltimore: Williams and Wilkins.
- ^ Murray RG (1984). "The higher taxa, or, a place for everything...?". In Krieg NR, Holt JC (eds.). Bergey's Manual of Systematic Bacteriology. Vol. 1 (1st ed.). Baltimore: Williams and Wilkins. pp. 31–34.
- ^ Woese CR (June 1987). "Bacterial evolution". Microbiological Reviews. 51 (2): 221–271. doi:10.1128/MMBR.51.2.221-271.1987. PMC 373105. PMID 2439888.
- ^ Brenner DJ, Krieg NA, Staley JT (July 26, 2005) [1984(Williams & Wilkins)]. "Introductory Essays". In Garrity GM (ed.). Bergey's Manual of Systematic Bacteriology. Vol. 2A (2nd ed.). New York: Springer. p. 304. ISBN 978-0-387-24143-2. British Library no. GBA561951.
- ^ a b Cavalier-Smith T (July 2006). "Rooting the tree of life by transition analyses". Biology Direct. 1: 19. doi:10.1186/1745-6150-1-19. PMC 1586193. PMID 16834776.
- ^ Krieg NR, Ludwig W, Whitman WB, Hedlund BP, Paster BJ, Staley JT, et al. (November 24, 2010) [1984(Williams & Wilkins)]. "The Bacteroidetes, Spirochaetes, Tenericutes (Mollicutes), Acidobacteria, Fibrobacteres, Fusobacteria, Dictyoglomi, Gemmatimonadetes, Lentisphaerae, Verrucomicrobia, Chlamydiae, and Planctomycetes". In Garrity GM (ed.). Bergey's Manual of Systematic Bacteriology. Vol. 4 (2nd ed.). New York: Springer. p. 908. ISBN 978-0-387-95042-6. British Library no. GBA561951.
- ^ Battistuzzi FU, Hedges SB (February 2009). "A major clade of prokaryotes with ancient adaptations to life on land". Molecular Biology and Evolution. 26 (2): 335–343. doi:10.1093/molbev/msn247. PMID 18988685.
- ^ Coleman GA, Davín AA, Mahendrarajah TA, Szánthó LL, Spang A, Hugenholtz P, et al. (May 2021). "A rooted phylogeny resolves early bacterial evolution". Science. 372 (6542): eabe0511. doi:10.1126/science.abe0511. hdl:1983/51e9e402-36b7-47a6-91de-32b8cf7320d2. PMID 33958449. S2CID 233872903.
- ^ Léonard RR, Sauvage E, Lupo V, Perrin A, Sirjacobs D, Charlier P, et al. (February 2022). "Was the Last Bacterial Common Ancestor a Monoderm after All?". Genes. 13 (2): 376. doi:10.3390/genes13020376. PMC 8871954. PMID 35205421.