What is the Smallest living organism?

Answer 1

a cell

Answer 2

This depends a little on how you define the term 'living'. If you consider viruses to be alive, then Porcine circovirus strain two is only 17nm in diameter. If you don't believe that viruses are alive, then some nanobes get to be about 20nm in diameter. The smallest organisms yet found that are unarguably alive are Nanoarcheum equitans a type of archea that can be as small as 400nm in diameter, C. rudii a type of proteobacterium, and possibly Sphingomonas strain RR2B56 which has not been adequately studied yet. Which one is smallest depends on the criteria (diameter, genome length, etc.).

Answer 3

The smallest organism found on Earth can be measured using a variety of different methods, and can be defined as the smallest by volume, mass, height, or length. Because there is some dispute over what the definition of life is and what entities qualify as organisms, the actual "smallest organism" (microorganisms) may be unclear. A further complication is the incomplete nature of scientific knowledge: it is possible that the smallest organism has yet to be discovered. In terms of size, some possible candidates include:

Viruses

Biologists consider viruses to be non-living because they lack a cellular structure and cannot metabolize by themselves, requiring a host cell to replicate and synthesise new products. A minority of scientists hold that because viruses do have genetic material and can employ the metabolism of their host, they can be considered organisms. For example, the Porcine circovirus 2 is a single stranded DNA virus having a capsid diameter of 17 nm.

Nanobes

Nanobes are thought by some to be the smallest known organism, about one tenth the size of the smallest known bacteria. Nobes, tiny filamental structures first found in some rocks and sediments, were first described in 1996 by Philipa Uwins of the University of Queensland. The smallest are 20 nm long. Some researchers believe them to be merely crystal growths, but a purported find of DNA in nanobe samples may prove otherwise. They are similar to the life-like structures found in ALH84001, the famous Mars meteorite from the Antarctic.

Nanoarchaeum

Nanoarchaeum equitans is a species of tiny microbe discovered in 2002 in a hydrothermal vent off the coast of Iceland by Karl Stetter. A thermophile that grows in near-boiling temperatures, Nanoarchaeum appears to be an obligatory symbiont on the archaeon Ignicoccus: it must be in contact with the host organism to survive. Its cells are only 400 nm in diameter, making it the smallest known living organism, with the possible exception of nanobes (if they are considered to be living). As of 2005 it remains the smallest non-viral genome ever sequenced.

Mycoplasma genitalium

Mycoplasma genitalium, a parasitic bacterium which lives in the primate 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 ultramicrobacteria Sphingomonas sp strain RB2256 is reported to have passed through 220 nm ultrafilter. A complicating factor is nutrient-downsized bacteria, bacteria that become much smaller due to a lack of available nutrients.

Answer 4

The smallest living organism is believed to be a type of bacteria called Mycoplasma genitalium, which has a size of approximately 200-300 nanometers.

Answer 5

Nano archea