Viruses of Mycoplasmas and Spiroplasmas

The term mycoplasma refers to a group of microorganisms (Class Mollicutes, Order Mycoplasmatales), previously known as pleuropneumonia-like organisms or PPLO. The many different isolates have been cataloged into the genera mycoplasma, acholeplasma, ureaplasma or T-strains, spiroplasma, thermoplasmn, and anaeroplasma. Mycoplasmas are clinically important microorganisms, and include the etiologic agents of a variety of plant and animal diseases. In human studies, mycoplasma pneumoniae has been found to be a pathogen and other mycoplasmas (of unknown etiology) have been isolated in clinical situations. Mycoplasmas are also frequently found as contaminants in tissue cultures. The biology of the mycoplasmas has been reviewed recently and some of their properties are summarized in this chapter. These prokaryotes do not have cell walls and are bounded by a single lipoprotein cell membrane. Mycoplasma, ureaplasma, spiroplasma, and anaeroplasma require sterol for growth. Some mycoplasma isolates are the smallest cells that have been found, and the genome sizes of the mycoplasma and ureaplasma are among the smallest reported.