The Firmicutes 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.

There is currently no way of detecting a bacterium as belonging to Firmicutes as the phylum is highly diverse in phenotypic characteristics due to promiscusious plasmid exchange across species and genera of this phyla.

The division Firmicutes as part of the gut flora has been shown to be involved in energy resorption and obesity. ^[1]

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. It is likely these groups will undergo revision.

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

• Enterococcus
• Lactobacillus
• Lactococcus
• Leuconostoc
• Pediococcus
• Streptococcus

Clostridia

• Acetobacterium
• Clostridium
• Eubacterium
• Heliobacterium
• Heliospirillum
• Pectinatus
• Sporomusa

Mollicutes

• Mycoplasma
• Spiroplasma
• Ureaplasma
• Erysipelothrix'

References

1. ^ Ley RE, Turnbaugh PJ, Klein S, Gordon JI. Microbial ecology: human gut microbes associated with obesity. Nature. 2006 Dec 21;444(7122):1022-3.

• Seth Borenstein "Scientists link weight to gut bacteria" , Yahoo News, December 20 2006 (Link dead as of 22:07, 14 January 2007 (UTC))
• ROBIN MARANTZ HENIG "Fat Factors" , New York Times Magazine, August 13 2006
• (Ley et al. 2006) "Obesity alters gut microbial ecology" , Proceedings of the National Academy of Sciences of the United States of America, August 2 2005