color = lightgrey
name = Firmicutes

image_width = 220px
image_caption = "Bacillus subtilis", Gram stained
regnum = Bacteria
divisio = Firmicutes
subdivision_ranks = Classes
subdivision =
The Firmicutes (Latin: "firmus", strong, and "cutis", skin, referring to the cell wall) are a division of bacteria, most of which have Gram-positive cell wall structure. A few, the Mollicutes or mycoplasmas, lack cell walls altogether and so do not respond to Gram staining, but still lack the second membrane found in other Gram-negative forms. Others, such as Megasphaera, Pectinatus, Selenomonas, and Zymophilus have a porous pseudo-outer-membrane that causes them to stain Gram-negative. Originally the Firmicutes were taken to include all Gram-positive bacteria, but more recently they tend to be restricted to a core group of related forms, called the low G+C group in contrast to the Actinobacteria. They have round cells, called cocci (singular coccus), or rod-shaped forms.

Many "Firmicutes" produce endospores, which are resistant to desiccation and can survive extreme conditions. They are found in various environments, and some notable pathogens. Those in one family, the heliobacteria, produce energy through photosynthesis. Firmicutes play an important role in beer, wine, and cider spoilage.


The group is typically divided into the Clostridia, which are anaerobic, the Bacilli, which are obligate or facultative aerobes, and the Mollicutes. On phylogenetic trees the first two groups show up as paraphyletic or polyphyletic, as do their main genera, "Clostridium" and "Bacillus". It is likely these groups will undergo revision.


While there are currently more than 274 genera within the Firmicutes phylum, notable genera of Firmicutes include:

Bacilli, order Bacillales
* "Bacillus"
* "Listeria"
* "Staphylococcus"Bacilli, order Lactobacillales
* "Enterococcus"
* "Lactobacillus"
* "Lactococcus"
* "Leuconostoc"
* "Pediococcus"
* "Streptococcus"Clostridia
* "Acetobacterium"
* "Clostridium"
* "Eubacterium"
* "Heliobacterium"
* "Heliospirillum"
* "Megasphaera"
* "Pectinatus"
* "Selenomonas"
* "Zymophilus"
* "Sporomusa"Mollicutes
* "Mycoplasma"
* "Spiroplasma"
* "Ureaplasma"
* "Erysipelothrix"

Health implications

The division "Firmicutes" as part of the gut flora has been shown to be involved in energy resorption and obesity.Ley RE, Turnbaugh PJ, Klein S, Gordon JI. Microbial ecology: human gut microbes associated with obesity. Nature. 2006 Dec 21;444(7122):1022-3.] [cite news | last=Henig| first=Robin Marantz| url=| title=Fat Factors | date=2006-08-13| publisher=New York Times Magazine| accessdate=2008-09-28] [cite journal |author=Ley RE, Bäckhed F, Turnbaugh P, Lozupone CA, Knight RD, Gordon JI |title=Obesity alters gut microbial ecology |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=102 |issue=31 |pages=11070–5 |year=2005 |month=August |pmid=16033867 |pmc=1176910 |doi=10.1073/pnas.0504978102 |url= |accessdate=2008-09-28]

Laboratory detection

While there has historically not been a way to categorically define a given bacterium as belonging to Firmicutes as the phylum is highly diverse in phenotypic characteristics due to promiscuous plasmid exchange across species and genera of this phyla, the presence of "Firmicutes" can now be detected by real-time PCR using the methodologies recently described. [cite journal |author=Haakensen M, Dobson CM, Deneer H, Ziola B |title=Real-time PCR detection of bacteria belonging to the Firmicutes Phylum |journal=Int. J. Food Microbiol. |volume=125 |issue=3 |pages=236–41 |year=2008 |month=July |pmid=18501458 |doi=10.1016/j.ijfoodmicro.2008.04.002 |url= |accessdate=2008-09-28]


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