Clostridia

Clostridia is a highly polyphyletic class of bacteria within Bacillota, including the genus Clostridium and other similar genera. Members are distinguished from the Bacilli by their lack of aerobic respiration: they are obligate anaerobes for which oxygen is toxic. Species of Clostridia are often, but not always, Gram-positive and have the ability to form spores. Studies show the class is not a monophyletic group and its internal relationships are not fully settled; most members currently sit in a single order, Clostridiales, that is itself not a natural grouping and is likely to be redefined.