Firmicutes
Bacillus subtilis, Gram stained
Scientific classification
Domain:	Bacteria
Phylum:	Firmicutes
Classes
Bacilli Bacillales Lactobacillales Clostridia Clostridiales Halanaerobiales Natranaerobiales Thermoanaerobacterales Erysipelotrichia Erysipelotrichales Negativicutes Selenomonadales Thermolithobacteria Thermolithobacterales

The Firmicutes (Latin: firmus, strong, and cutis, skin, referring to the cell wall) are a phylum of bacteria, most of which have Gram-positive cell wall structure.^[1] A few, however, such as Megasphaera, Pectinatus, Selenomonas and Zymophilus, have a porous pseudo-outer-membrane that causes them to stain Gram-negative. Scientists once classified the Firmicutes to include all Gram-positive bacteria, but have recently defined them to be of 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-like forms (bacillus).

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

Classes[link]

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.^[2]

Phylogeny[link]

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) ^[3] and National Center for Biotechnology Information (NCBI)^[4] and the phylogeny is based on 16S rRNA-based LTP release 106 by The All-Species Living Tree Project ^[5]

Notes:
♠ Strains found at the National Center for Biotechnology Information (NCBI) but not listed in the List of Prokaryotic names with Standing in Nomenclature LPSN

Genera[link]

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

Bacilli, order Bacillales

Bacilli, order Lactobacillales

Clostridia

Erysipelotrichi

Health implications[link]

Firmicutes make up the largest portion of the mouse and human gut microbiome.^[6] The division Firmicutes as part of the gut flora has been shown to be involved in energy resorption and obesity.^[6][7][8]

Laboratory detection[link]

While there has up to this point in time 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 its members' promiscuous plasmid exchange across species and genera, the presence of Firmicutes can now be detected by real-time PCR using the methodologies recently described.^[9]

References[link]

External links[link]

• Phylum "Firmicutes" - J.P. Euzéby: List of Prokaryotic names with Standing in Nomenclature