Ultramicrobacteria are bacteria that are smaller than 0.1 μm3 under all growth conditions.[1][2][3] This term was coined in 1981, describing cocci in seawater that were less than 0.3 μm in diameter.[4] Ultramicrobacteria have also been recovered from soil and appear to be a mixture of Gram-positive, Gram-negative and cell-wall-lacking species.[5][2] Ultramicrobacteria possess a relatively high surface-area-to-volume ratio due to their small size, which aids in growth under oligotrophic (i.e. nutrient-poor) conditions.[2] The relatively small size of ultramicrobacteria also enables parasitism of larger organisms;[2] some ultramicrobacteria have been observed to be obligate or facultative parasites of various eukaryotes and prokaryotes.[1][2]One factor allowing ultramicrobacteria to achieve their small size seems to be genome minimization[1][2] such as in the case of the ultramicrobacterium P. ubique whose small 1.3 Mb genome is seemingly devoid of extraneous genetic elements like non-coding DNA, transposons, extrachromosomal elements etc.[2] However, genomic data from ultramicrobacteria is lacking[2] since the study of ultramicrobacteria, like many other prokaryotes, is hindered by difficulties in cultivating them.[3]
Ultramicrobacteria are commonly confused with ultramicrocells, the latter of which are the dormant, stress-resistant forms of larger cells that form under starvation conditions[1][2][7] (i.e. these larger cells downregulate their metabolism, stop growing and stabilize their DNA to create ultramicrocells that remain viable for years[1][8]) whereas the small size of ultramicrobacteria is not a starvation response and is consistent even under nutrient-rich conditions.[3]
The term "nanobacteria" is sometimes used synonymously with ultramicrobacteria in the scientific literature,[2] but ultramicrobacteria are distinct from the purported nanobacteria or "calcifying nanoparticles", which were proposed to be living organisms that were 0.1 μm in diameter.[9] These structures are now thought to be non-living,[10] and likely precipitated particles of inorganic material.[11][12]
See also[edit]
- L-form bacteria
- Mycoplasma – smallest known bacteria (300 nm)
- Nanoarchaeum – smallest known archaeum (400 nm)
- Nanobacteria – possible lifeforms smaller than bacteria (<200 nm)
- Nanobe – possible smallest lifeforms (20 nm)
- Pandoravirus – one of the largest known viruses (1000 nm)
- Parvovirus – smallest known viruses (18–28 nm)
- Pithovirus – largest known virus (1500 nm)
- Prion – smallest known infectious agent (≈10 nm)
- ND5 and MY14T – two aerobic, Gram-negative, rod-shaped bacteria[13]
https://en.wikipedia.org/wiki/Ultramicrobacteria
above. tool the pot
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