Scientific classification
Kingdom: Bacteria
Phylum: Firmicutes
Class: Clostridia

The Clostridia are a highly polyphyletic class of Firmicutes, including Clostridium and other similar genera. They are distinguished from the Bacilli by lacking aerobic respiration. They are obligate anaerobes and oxygen is toxic to them. Species of the genus Clostridium are all Gram-positive and have the ability to form spores. Studies show they are not a monophyletic group, and their relationships are not entirely certain. Currently most are placed in a single order called Clostridiales, but this is not a natural group and is likely to be redefined in the future.

Most species of the genus Clostridium are saprophytic organisms found in many places in the environment, most notably the soil. However, the genus does contain some human pathogens (outlined below). The toxins produced by certain members of the Clostridium genus are among the most dangerous known. Examples are tetanus toxin (known as tetanospasmin) produced by C. tetani and botulinum toxin produced by C. botulinum.

Notable species of this class include:

Heliobacteria are also members of the class Clostridia.

Some of the enzymes produced by this group are used in bioremediation.


The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) [1] and National Center for Biotechnology Information (NCBI)[2] and the phylogeny is based on 16S rRNA-based LTP release 106 by The All-Species Living Tree Project [3]

  Clostridia s.s.

Peptococcaceae 2

Peptococcaceae 1


Peptococcaceae 3





Peptococcaceae 4

Dethiobacter alkaliphilus


Anaerobranca {Clostridiales Family XIV. Incertae Sedis}


Garciella nitratireducens

Clostridiaceae 3

Clostridiales Family XI. Incertae Sedis [incl. Anaerosphaera aminiphila]

Eubacterium angustum

Proteiniborus ethanoligenes

Clostridiaceae 4 [incl. various Clostridium ssp.]

Clostridiales Family XII. Incertae Sedis

Clostridiales Family XIII. Incertae Sedis [incl. various Eubacterium spp.]

Clostridiaceae 2 [incl. various Clostridium ssp.]

Peptostreptococcaceae [incl. Clostridiales Family XIX. Incertae Sedis and various Clostridium & Eubacterium spp.]

  Clostridiales s.s.

Thermoanaerobacterales Unnamed clade III [incl. Caldicoprobacter]

Clostridiaceae 1 [incl. various Eubacterium spp.]

Gracilibacter thermotolerans

Lutispora thermophila

Ruminococcaceae [incl. Bacteroides cellulosolvens, Butyricicoccus pullicaecorum, Gemmiger formicilis, Oscillibacter valericigenes, Saccharofermentans acetigenes and various Clostridium & Eubacterium spp.]

Lachnospiraceae [incl. Anaerosporobacter mobilis, Desulfotomaculum guttoideum, Fusobacterium naviforme, Lactobacillus rogosae, Lactonifactor longoviformis, various Bacteroides, Clostridium, Eubacterium, & Ruminococcus ssp.]

Unassigned Clostridia s.s.

  • Catabacteraceae ♠ Lau et al. 2007
    • Catabacter hongkongensisLau et al. 2007
  • Christensenellaceae Morotomi et al. 2012
    • Christensenella minuta Morotomi et al. 2012
  • Defluviitaleaceae Jabari et al. 2012
    • Defluviitalea saccharophila Jabari et al. 2012

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

See also