The genus, or variety, of micro-organisms that produce spores, thus enabling them to survive under adverse conditions. They normally grow in soil, water and decomposing plant and animal matter, where they play an important part in the process of PUTREFACTION. Among the important members of the group, or genus, are Clostridium welchii, Cl. septicum and Cl. oedematiens, the causes of gas gangrene (see GANGRENE); Cl. tetani, the cause of TETANUS; and Cl. botulinum, the cause of BOTULISM.