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Negativicutes
Scientific classification
Domain:	Bacteria
Phylum:	Bacillota
Class:	Negativicutes Marchandin et al. 2010
Orders and families
Selenomonadales Selenomonadaceae Sporomusaceae Acidaminococcales Acidaminococcaceae Veillonellales Veillonellaceae
Synonyms
"Selenomonadia" Oren, Parte & Garrity 2016 "Selenobacteria" Cavalier-Smith 1992 stat. nov. Cavalier-Smith 2006

The Negativicutes are a class of bacteria in the phylum Bacillota, whose members have a peculiar cell wall with a lipopolysaccharide outer membrane which stains gram-negative, unlike most other members of the Bacillota. Although several neighbouring Clostridia species (firmicute bacteria) also stain gram-negative, the proteins responsible for the unusual diderm structure of the Negativicutes may have actually been laterally acquired from Pseudomonadota (formerly Proteobacteria). Additional research is required to confirm the origin of the diderm cell envelope in the Negativicutes.

Most members of this class are obligate anaerobes, and occur in habitats such as rivers, lakes, and the intestines of vertebrates. They range from spherical forms, such as Megasphaera and Veillonella, to curved rods, as typified by the selenomonads. Selenomonas has a characteristic crescent shape, with flagella inserted on the concave side, while Sporomusa is similar, but nonmotile. Their names refer to this distinctive morphology: selene means moon, and musa means banana.

Taxonomy

The class currently consists of 32 validly named genera across three orders and four families. The orders Veillonellales and Acidaminococcales each contain a single family, Veillonellaceae and Acidaminococcaceae, respectively, while the order Selenomonadales contains two families, Selenomonadaceae and Sporomusaceae.

Molecular signatures

Historically, the Negativicutes consisted of a single order, the Selenomonadales, and two families, Veillonellaceae and Acidaminococcaceae based on 16S rRNA gene sequence similarity. However, these groupings did not include several members within the Negativicutes that branched outside of the two families. The current taxonomic view is inclusive of these members who have been validly assigned to the families Selenomonadaceae and Sporomusaceae within the emended Selenomonadales order. Molecular markers in the form of conserved signature indels (CSIs) and proteins (CSPs) justify the present taxonomic divisions. These molecular markers are found at each taxonomic rank, and their distribution is in agreement with the observed phylogenetic branching.

Many works have implicated that the Negativicutes should be reclassified as an order within the class Clostridia, based on close phylogenetic branching, and the observation that the spore-forming members of the Negativicutes share similar sporulation genes as the Clostridia, and that both stain gram-negative. However, the heterogeneity of members within the Negativicutes, as well as the distribution of molecular signatures, supports the view that the Negativicutes are in fact an independent class within the Bacillota, with Clostridia as their closest phylogenetic neighbours. Additionally, several CSIs and CSPs have been found to be uniquely shared among all Negativicutes, while no CSIs have been found to be shared by both Negativicutes and Clostridia.

Phylogeny

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI)

See also

• List of bacterial orders
• List of bacteria genera

References

1. ^ Sutcliffe IC (2010). "A phylum level perspective on bacterial cell envelope architecture". Trends Microbiol. 18 (10): 464–470. doi:10.1016/j.tim.2010.06.005. PMID 20637628.
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3. Campbell C, Sutcliffe IC, Gupta RS (2014). "Comparative proteome analysis of Acidaminococcus intestini supports a relationship between outer membrane biogenesis in Negativicutes and Proteobacteria" (PDF). Arch Microbiol. 196 (4): 307–310. doi:10.1007/s00203-014-0964-4. PMID 24535491. S2CID 253722630.
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5. ^ Marchandin, H.; Teyssier, C.; Campos, J.; Jean-Pierre, H.; Roger, F.; Gay, B.; Carlier, J. -P.; Jumas-Bilak, E. (2009). "Negativicoccus succinicivorans gen. nov., sp. nov., isolated from human clinical samples, emended description of the family Veillonellaceae and description of Negativicutes classis nov., Selenomonadales ord. nov. and Acidaminococcaceae fam. nov. in the bacterial phylum Firmicutes". International Journal of Systematic and Evolutionary Microbiology. 60 (6): 1271–1279. doi:10.1099/ijs.0.013102-0. PMID 19667386.
6. Sayers; et al. "Negativicutes". National Center for Biotechnology Information (NCBI) taxonomy database. Retrieved 2013-03-20.
7. ^ Campbell C, Adeolu M, Gupta RS (2015). "Genome-based taxonomic framework for the class Negativicutes: division of the class Negativicutes into the orders Selenomonadales emend., Acidaminococcales ord. nov. and Veillonellales ord. nov". Int J Syst Evol Microbiol. 65 (9): 3203–3215. doi:10.1099/ijs.0.000347. PMID 25999592.
8. Ludwig W, Schleifer K-H, Whitman, WB (2009) Revised road map to the phylum Firmicutes. In: Bergey’s Manual of Systematic Bacteriology, vol. 3, 2nd edn. pp. 1–13. Eds P. De Vos, G. M. Garrity, D. Jones, N. R. Krieg, W. Ludwig, F. A. Rainey, K. H. Schleifer & W. B. Whitman Springer-: New York.
9. ^ Yutin N, Galperin MY (2013). "A genomic update on clostridial phylogeny: Gram-negative spore formers and other misplaced clostridia". Environ Microbiol. 15 (10): 2631–2641. doi:10.1111/1462-2920.12173. PMC 4056668. PMID 23834245.
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11. Merchandin H, Jumas-Bilak E (2014) The family Veillonellaceae. In: The Prokaryotes, vol. 7, 4th edn. pp. 433–453. Eds E. Rosenberg, E. DeLong, S. Lory, E. Stackebrandt & F. Thompson Springer-: Berlin, Heidelberg.
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13. J.P. Euzéby. "Negativicutes". List of Prokaryotic names with Standing in Nomenclature (LPSN). Retrieved 2022-09-09.
14. Sayers; et al. "Negativicutes". National Center for Biotechnology Information (NCBI) taxonomy database. Retrieved 2022-09-09.
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• Negativicutes
• Bacteria classes