<Tr> <Th_colspan="2"> Synonyms </Th> </Tr> <Tr> <Td_colspan="2"> <P> Eubacteria Woese & Fox, 1977 </P> </Td> </Tr> <P> Eubacteria Woese & Fox, 1977 </P> <P> Bacteria (/ bækˈtɪəriə / (listen); common noun bacteria, singular bacterium) constitute a large domain of prokaryotic microorganisms . Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals . Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats . Bacteria inhabit soil, water, acidic hot springs, radioactive waste, and the deep portions of Earth's crust . Bacteria also live in symbiotic and parasitic relationships with plants and animals . Most bacteria have not been characterised, and only about half of the bacterial phyla have species that can be grown in the laboratory . The study of bacteria is known as bacteriology, a branch of microbiology . </P>

A culture containing only one type of species of bacterium