Autotrophic organisms that survive and reproduce by inorganic nutrition are the corresponding words of organic vegetative organisms. Organisms that assimilate carbon by using energy obtained from chemical dark reactions such as respiration or photochemical reactions are called chemoautotrophs and photoautotrophs respectively. Representative examples of autotrophic microorganisms are red sulfur-free bacteria, red sulfur bacteria, green sulfur bacteria, nitrifying bacteria, sulfur bacteria, hydrogen bacteria, iron bacteria and carbon monoxide bacteria (except denitrifying bacteria).