Which animal/plant/anything has smallest length genome?


3 Answers 3


Since you said plant/animal/anything, I offer the smallest genomes in various categories...

(Kb means Kilobases, Mb means Megabases. 1 Kb = 1000 base pairs, 1Mb = 1000Kb)


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    $\begingroup$ Well done! How did you find these? $\endgroup$
    – user560
    Commented Mar 12, 2012 at 16:36
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    $\begingroup$ The plant and bacterial ones I had floating around in my memory having read about them previously, so a bit of googling confirmed the names. The animal ones I got from the Animal Genome Size DB, and from Wikipedia. I guessed that viral genomes would be the smallest, so I also searched for the smallest viral genome. Then I went back to the literature (by searching Google Scholar for organism name + "genome size") to check all my facts and provide reliable references. $\endgroup$ Commented Mar 12, 2012 at 18:43
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    $\begingroup$ Nice answer Richard. $\endgroup$
    – Poshpaws
    Commented Mar 13, 2012 at 11:38
  • $\begingroup$ Smallest free-living bacterial genome: Nanoarchaeum eqitans at 491Kb (Waters et al., 2003) I downloaded this paper it says that this is archaea and its obligate symbiont not a free living bacteria. Please read carefully and then upload it. $\endgroup$
    – manish
    Commented Aug 14, 2015 at 10:10
  • $\begingroup$ "Smallest genome of anything" is wrong. There are virus-like elements like viroids with as little as ~200 bp 'genomes'. Some viroids have as little as one RNA enzyme, others have not even this. $\endgroup$
    – arara
    Commented Feb 16, 2023 at 13:22

I want to say Mycoplasma genitalium with a genome size of 582,970 bp. Turns out the answer is Nanoarchaeum eqitans with a genome of 490,885 bp.



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    $\begingroup$ That's the smallest genome of a free-living organism. And until 2003 you would have been right about Mycoplasma, which were previously the smallest known in that category. $\endgroup$ Commented Mar 12, 2012 at 0:38

Both Mycoplasma genitalium and Nanoarchaeum equitans are obligate parasites / endosymbionts. This means that they depend heavily on their host to support their vital functions and they have lost many of their own genes.

A really free-living organism with an extremely small genome (~1309 kbp, 1354 genes) is the heterotrophic marine alpha-proteobacterium Pelagibacter ubique [1].

See a larger analysis here: https://alamot.github.io/smallest_genome/

[1]: https://www.ncbi.nlm.nih.gov/pubmed/16109880 Giovannoni SJ, Tripp HJ, Givan S, Podar M, Vergin KL, et al. (2005). «Genome streamlining in a cosmopolitan oceanic bacterium». Science 309: 1242–1245.


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