bacteria - a large group of unicellular or multicellular organisms, lacking chlorophyll, multiplying rapidly by simple fission, some species developing a highly resistant resting ("spore") phase. They are the principle members of the prokaryotes, whose genetic material is not packaged into chromosomes contained in nucleus. Instead they have a single circle of DNA free in the cytoplasm, which reproduces by a "rolling circle" mechanism. They lack mitochondria, oxidative phosphorylation, occuring across the plasma membrane, and they are bounded by a cell wall situated outside and separated from the plasma membrane by a periplasmic space ... Since Pasteur's time they have been actively studied and classified in relation to disease but they are also important in the production of chemicals, enzymes and antibiotics.
