Firmicutes

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.[3] 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.[4]

Phylogeny

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) [5] and National Center for Biotechnology Information (NCBI)[6] and the phylogeny is based on 16S rRNA-based LTP release 111 by The All-Species Living Tree Project [7]

?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

More than 274 genera were considered as of 2016 to be within the Firmicutes phylum, notable genera of Firmicutes include:

Bacilli, order Bacillales

Bacilli, order Lactobacillales

Clostridia

Erysipelotrichia

Health implications

Firmicutes make up the largest portion of the mouse and human gut microbiome.[8] The division Firmicutes as part of the gut flora has been shown to be involved in energy resorption and obesity.[9][10][11]

See also: Infectobesity

Presence of Christensenella, in class Clostridia and also isolated from human faeces, has been found to correlate with lower body mass index.[12]

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.[13]

References

  1. ↑ Gibbons, N. E. & Murray, R. G. E. 1978. Proposals concerning the higher taxa of bacteria. Int J Syst Bacteriol 28:1–6, (PDF)
  2. ↑ Murray, R.G.E. (1984). The higher taxa, or, a place for everything...?. In: N.R. Krieg & J.G. Holt (ed.) Bergey's Manual of Systematic Bacteriology, vol. 1, The Williams & Wilkins Co., Baltimore, p. 31-34.
  3. ↑ "Firmicutes" at Dorland's Medical Dictionary
  4. ↑ Wolf M, Müller T, Dandekar T, Pollack JD (May 2004). "Phylogeny of Firmicutes with special reference to Mycoplasma (Mollicutes) as inferred from phosphoglycerate kinase amino acid sequence data". Int. J. Syst. Evol. Microbiol. (Comparative Study). 54 (Pt 3): 871–5. doi:10.1099/ijs.0.02868-0. PMID 15143038.
  5. ↑ J.P. Euzéby. "Firmicutes". List of Prokaryotic names with Standing in Nomenclature (LPSN). Archived from the original on January 27, 2013. Retrieved 2013-03-20.
  6. ↑ Sayers; et al. "Firmicutes". National Center for Biotechnology Information (NCBI) taxonomy database. Retrieved 2013-03-20.
  7. ↑ All-Species Living Tree Project."16S rRNA-based LTP release 111 (full tree)" (PDF). Silva Comprehensive Ribosomal RNA Database. Retrieved 2013-03-20.
  8. ↑ Ley RE, Peterson DA, Gordon JI (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.
  9. ↑ Ley RE, Turnbaugh PJ, Klein S, Gordon JI (2006). "Microbial ecology: human gut microbes associated with obesity". Nature (Clinical Trial). 444 (7122): 1022–3. doi:10.1038/4441022a. PMID 17183309.
  10. ↑ Henig, Robin Marantz (2006-08-13). "Fat Factors". New York Times Magazine. Retrieved 2008-09-28.
  11. ↑ Ley RE, Bäckhed F, Turnbaugh P, Lozupone CA, Knight RD, Gordon JI (August 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 1176910Freely accessible. PMID 16033867. Retrieved 2008-09-28.
  12. ↑ Goodrich, Julia K.; Waters, Jillian L.; Poole, Angela C.; Sutter, Jessica L.; Koren, Omry; Blekhman, Ran; Beaumont, Michelle; Van Treuren, William; Knight, Rob; Bell, Jordana T.; Spector, Timothy D.; Clark, Andrew G.; Ley, Ruth E. (2014). "Human Genetics Shape the Gut Microbiome". Cell. 159 (4): 789–799. doi:10.1016/j.cell.2014.09.053. ISSN 0092-8674.
  13. ↑ Haakensen M, Dobson CM, Deneer H, Ziola B (July 2008). "Real-time PCR detection of bacteria belonging to the Firmicutes Phylum". Int. J. Food Microbiol. (Research Support). 125 (3): 236–41. doi:10.1016/j.ijfoodmicro.2008.04.002. PMID 18501458. Retrieved 2008-09-28.
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