page_title: Smallest organisms
section_title: Mycoplasma genitalium
hierarchical_section_title: Smallest organisms / Microorganisms / Mycoplasma genitalium
caption_attribution_description: Deutsch: Bild über den Reitenden UrzwergEnglish: Image of Nanoarchaeum equitans
context_page_description: The smallest organisms found on Earth can be determined according to various aspects of organism size, including volume, mass, height, length, or genome size.
  Given the incomplete nature of scientific knowledge, it is possible that the smallest organism is undiscovered. Furthermore, there is some debate over the definition of life, and what entities qualify as organisms; consequently the smallest known organism is debatable.
context_section_description: Mycoplasma genitalium, a parasitic bacterium which lives in the primate bladder, waste disposal organs, genital, and respiratory tracts, is thought to be the smallest known organism capable of independent growth and reproduction. With a size of approximately 200 to 300 nm, M. genitalium is an ultramicrobacterium, smaller than other small bacteria, including rickettsia and chlamydia. However, the vast majority of bacterial strains have not been studied, and the marine ultramicrobacterium Sphingomonas sp. strain RB2256 is reported to have passed through a 220 nm ultrafilter. A complicating factor is nutrient-downsized bacteria, bacteria that become much smaller due to a lack of available nutrients.
caption: Nanoarchaeum equitans and archaeon host, Ignicoccus
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