The Clostridia are a highly polyphyletic class of Bacillota, 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 class Clostridia are often but not always 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.
The Clostridiaceae are a family of the bacterial class Clostridia, and contain the genus Clostridium.
Rubrobacter is a genus of Actinomycetota. It is radiotolerant and may rival Deinococcus radiodurans in this regard.
The Halanaerobiales are an order of bacteria placed within the class Clostridia, and encompassing two families, the Halanaerobiaceae and the Halobacteroidaceae. Originally placed within the highly polyphyletic class Clostridia, according to the NCBI and LPSN, it is now thought to lie outside the Bacillota. Halanaerobiales are halophilic obligate anaerobes with a fermentative or homoacetogenic metabolism.
The Thermoanaerobacterales is a polyphyletic order of bacteria placed within the polyphyletic class Clostridia, and encompassing four families: the Thermoanaerobacteraceae, the Thermodesulfobiaceae, the Thermoanaerobacterales Family III. Incertae Sedis, and the Thermoanaerobacterales Family IV. Incertae Sedis, and various unplaced genera.
The Veillonellaceae are a family of the Clostridia, formerly known as Acidaminococcaceae. Bacteria in this family are grouped together mainly based on genetic studies, which place them among the Bacillota. Supporting this placement, several species are capable of forming endospores. However, they differ from most other Bacillota in having Gram-negative stains. The cell wall composition is peculiar.
Caldicellulosiruptor is a genus of thermophilic, anaerobic, Gram-positive, non-spore forming bacteria. Originally placed within the highly polyphyletic class Clostridia, order Thermoanaerobacterales and family Thermoanaerobacterales Family III according to the NCBI and LPSN, it is now thought to lie outside of the Bacillota. Caldicellulosiruptor is known to degrade and ferment complex carbohydrates from plant matter, such as cellulose and hemicellulose, and certain species in the genus have been identified as potential candidates for biofuel production.
Lentisphaerota is a phylum of bacteria closely related to Chlamydiota and Verrucomicrobiota.
The Negativicutes are a class of bacteria in the phylum Bacillota, whose members have a peculiar cell wall with a lipopolysaccharide outer membrane which stains gram-negative, unlike most other members of the Bacillota. Although several neighbouring Clostridia species also stain gram-negative, the proteins responsible for the unusual diderm structure of the Negativicutes may have actually been laterally acquired from Pseudomonadota. Additional research is required to confirm the origin of the diderm cell envelope in the Negativicutes.
Megasphaera is a genus of Bacillota bacteria classified within the class Negativicutes.
Sporichthya is a genus of bacteria in the family Sporichthyaceae.
The Cryptosporangiaceae are the only family of the order Cryptosporangiales, which is a part of the phylum Actinomycetota.
Kineococcus is an Actinomycete genus within the family Kineosporiaceae.
The family Thermodesulfobiaceae according to the LPSN is located within the order Thermoanaerobacterales and class Clostridia. However, according to the All-Species Living Tree Project it lies outside the clade Bacillota and the genus Caldanaerovirga does not belong to the clade, i.e. Thermodesulfobiaceae is polyphyletic.
The Thermaerobacter are an unassigned genus of bacteria placed within the class clostridia. Originally placed within the highly polyphyletic class Clostridia, order Clostridiales, according to the NCBI and LPSN, it is now thought to lie outside of the Bacillota.
Rarobacteraceae is a monotypic Actinomycetota family.
Ruaniaceae is an Actinomycete family with two monotypic genera.
Beutenbergiaceae is an Actinomycete family.
Bogoriellaceae is an Actinomycete family.
Moorella is a genus of bacteria belonging to the phylum Bacillota.
