mycoplasma

Any of a phylum of extremely small, parasitic bacteria that have a flexible cell membrane instead of a rigid cell wall, can assume a variety of shapes, are usually nonmotile, and are capable of forming colonies. Too small to be seen with a light microscope, mycoplasmas are thought to be the smallest organisms capable of independent growth. They are often pathogenic or parasitic in mammals and cause a number of important plant diseases, notably among citrus fruits. Mycoplasmas of the genus Mycoplasma are dependent upon sterols such as cholesterol for growth and cause several types of pneumonia in humans and animals.

See also phytoplasma