Even though the Schizomycetes, or bacteria, contain half a dozen subgroups that are as distinct from one another as bacteria are from blue-green algae, most bacteria share certain fundamental characteristics. There are three basic bacterial shapes: spherical, rod-shaped, and helically coiled. Spherical bacteria are known as cocci, rod-shaped as bacilli, and helical as spirilla.
Some bacteria remain together after cell division forming a multicellular aggregate where consecutive cells share cell walls. Indeed, most bacteria have cell walls which not only protect them from physical damage but also from bursting since most bacteria are hypertonic relative to their surrounding environment. Additionally, a bacterium can secrete a capsule, consisting of mucoid materials, over its cell wall that makes it more resistant to a host's defenses.
Some rod-shaped and spherical bacteria produce endospores, special resting cells that enable the organism to withstand extreme conditions of heat, cold, and drought. Endospores, which develop within vegetative bacterial cells, contain DNA and a small amount of other essential materials; they are surrounded by an impenetrable spore coat. Once the endospore is formed, the vegetative cell around it may disintegrate; when revived by favorable conditions, the endospore will give rise to a normal vegetative cell. Bacteria reproduce via binary fission, a process in which two daughter cells with an exact copy of the mother's
