Bacteria are classified in the kingdom known as 'Monera'. All prokaryotic organisms are placed in this kingdom. Additionally, all Monera are single celled organisms. The four other kingdoms, plantae, animalia, protista, and fungi are all composed of eukaryotic cells.
Bacteria can function in one of three modes.
They can be aerobic, anaerobic, or perform anaerobic respiration. Aerobic bacteria use oxygen as their terminal electron acceptor and hence produce only carbon dioxide and water. Anaerobic bacteria do not require oxygen and may therefore produce a variety of end-products, ranging from harmless fatty acids to the toxic gas hydrogen sulfide to the solvent acetone which can be produced by a bacterium common to soils, Clostridium acetobutylicum . During anaerobic respiration, an inorganic, oxygenated compound such as nitrate or sulfate serves as the terminal electron acceptor. Bacteria such as Alcaligenes denitrificans undergo anaerobic respiration and are therefore capable players when bioremediation is employed to clean various agricultural wastes.