n.
Group of microscopic, single-celled organisms that are prokaryotes .
They may have spherical, rodlike, or spiral shapes. They inhabit virtually all environments, including soil, water, organic matter, and the bodies of multicellular animals. Different types are distinguished in part by the structure of their cell walls, which is determined by gram stain . Many bacteria swim by means of flagella (see flagellum ). The DNA of most bacteria is found in a single circular chromosome and is distributed throughout the cytoplasm rather than contained within a membrane-enclosed nucleus. Though some bacteria can cause food poisoning and infectious diseases in humans, most are harmless and many are beneficial. They are used in various industrial processes, especially in the food industry (e.g., the production of yogurt, cheeses, and pickles). Bacteria are divided into eubacteria and archaebacteria . See also budding bacteria , coliform bacteria , cyanobacteria , denitrifying bacteria , nitrifying bacteria , sheathed bacteria , sulfur bacteria .