Firmicutes

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

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. 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

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.

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) and the phylogeny is based on 16S rRNA-based LTP release 111 by The All-Species Living Tree Project

?Thermodesulfobiaceae ?Synergistaceae {Clostridiales Family XV Incertae Sedis} Firmicutes s. s. ?Clostridium thermoamylolyticum ♠ Katkocin et al. 1985 Thermaerobacter Caldicellulosiruptor Thermoanaerobacteraceae Thermanaeromonas toyohensis Dictyoglomus Thermoanaerobacterales Unnamed clade I (incl. Fervidicola) Thermoanaerobacterales Unnamed clade II Gelria glutamica Clostridiales Family XVIII Incertae Sedis Sulfobacillus Clostridia s.s. (incl. Thermolithobacter, Negativicutes & Thermoanaerobacterales Unnamed clade III) Bacilli (incl. Erysipelotrichia & Mollicutes)

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

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

• Lactobacillus
• Leuconostoc

Clostridia

• Acetobacterium
• Clostridium
• Eubacterium
• Heliobacterium
• Heliospirillum
• Megasphaera
• Pectinatus
• Selenomonas
• Zymophilus
• Sporohalobacter
• Sporomusa

Erysipelotrichi

• Erysipelothrix

Health implications

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

See also: Infectobesity

Laboratory detection

It was once impossible 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, but the presence of Firmicutes can now be detected by real-time polymerase chain reaction (PCR) techniques.

External links

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