TAXONOMY: cellular organisms -> Bacteria -> Terrabacteria group -> Firmicutes -> Clostridia -> Clostridiales
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. Some species have been isolated from women with bacterial vaginosis. Notable species of this class include: *Clostridium perfringens (Gangrene, Food poisoning) *Clostridium difficile (Pseudomembranous colitis) *Clostridium tetani (Tetanus) *Clostridium botulinum (Botulism) *Clostridium acetobutylicum *Clostridium haemolyticum *Clostridium novyi *Clostridium novyi Clostridium oedematiens Heliobacteria are also members of the class Clostridia. Some of the enzymes produced by this group are used in bioremediation.
Specific differences have been found in blood group A-secretors demonstrating higher abundances of members of the Clostridiales family. [PMCID: PMC5625272]