phylum of bacteria

The Firmicutes are a phylum of bacteria, most of which have the Gram-positive type of cell walls.

Bacillus subtilis Gram.jpg
Bacillus subtilis, Gram stained
Scientific classification



The group is typically divided into the Clostridia, which are anaerobic, the Bacilli, which are aerobic, and the Mollicutes, a class of bacteria which do not have cell walls.

On phylogenetic trees, the first two groups show up as paraphyletic or polyphyletic, as do their main genera, Clostridium and Bacillus.[1]


Firmicutes make up the largest portion of the mouse and human gut microbiome.[2] The division Firmicutes as part of the gut flora has been shown to be involved in energy resorption and obesity.[3][4][5]


  1. Wolf M.; et al. (2004). "Phylogeny of Firmicutes with special reference to Mycoplasma (Mollicutes) as inferred from phosphoglycerate kinase amino acid sequence data". Int. J. Syst. Evol. Microbiol. 54 (Pt 3): 871–5. doi:10.1099/ijs.0.02868-0. PMID 15143038. Archived from the original on 2012-12-09. Retrieved 2014-03-28.
  2. Ley R.E; Peterson D.A. & Gordon J.I. (2006). "Ecological and evolutionary forces shaping microbial diversity in the human intestine". Cell (Review). 124 (4): 837–48. doi:10.1016/j.cell.2006.02.017. PMID 16497592. S2CID 17203181.{{cite journal}}: CS1 maint: uses authors parameter (link)
  3. Ley R.E. et al. (2006). "Microbial ecology: human gut microbes associated with obesity". Nature (Clinical Trial). 444 (7122): 1022–3. doi:10.1038/4441022a. PMID 17183309. S2CID 205034045.{{cite journal}}: CS1 maint: uses authors parameter (link)
  4. Henig, Robin Marantz (2006-08-13). "Fat Factors". New York Times Magazine. Retrieved 2008-09-28.
  5. Ley R.E.; et al. (2005). "Obesity alters gut microbial ecology". Proc. Natl. Acad. Sci. U.S.A. (Research Support). 102 (31): 11070–5. doi:10.1073/pnas.0504978102. PMC 1176910. PMID 16033867.