Ultramicrobacteria

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 nonworking genes, 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][6] (ie. these larger cells downregulate their metabolism, stop growing and stabilize their DNA to create ultramicrocells that remain viable for years[1][7]) 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.[8] These structures are now thought to be non-living,[9] and likely precipitated particles of inorganic material.[10][11]

See also
  • 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[12]

References
  1. Cavicchioli, Ricardo; Ostrowski, Martin (June 2003). Encyclopedia of Life Sciences. Nature Publishing Group. ISBN 9780470015902. Retrieved September 26, 2017.
  2. Duda, V; Suzina, N; Polivtseva, V; Boronin, A (2012). "Ultramicrobacteria: Formation of the Concept and Contribution of Ultramicrobacteria to Biology". Microbiology. 81 (4): 379–390. doi:10.1134/s0026261712040054.
  3. Janssen, Peter; Schuhmann, Alexandra; Mörschel, Erhard; Rainey, Frederick (April 1997). "Novel anaerobic ultramicrobacteria belonging to the verrucomicrobiales lineage of bacterial descent isolated by dilution culture from anoxic rice paddy soil". Applied and Environmental Microbiology. 63 (4): 1382–1388. PMC 168432.
  4. Torrella F, Morita RY (1 February 1981). "Microcultural Study of Bacterial Size Changes and Microcolony and Ultramicrocolony Formation by Heterotrophic Bacteria in Seawater". Appl. Environ. Microbiol. 41 (2): 518–527. PMC 243725. PMID 16345721.
  5. Iizuka T, Yamanaka S, Nishiyama T, Hiraishi A (February 1998). "Isolation and phylogenetic analysis of aerobic copiotrophic ultramicrobacteria from urban soil". J. Gen. Appl. Microbiol. 44 (1): 75–84. doi:10.2323/jgam.44.75. PMID 12501296.
  6. Velimirov, B. (2001). "Nanobacteria, Ultramicrobacteria and Starvation Forms: A Search for the Smallest Metabolizing Bacterium". Microbes and Environments. 16 (2): 67–77. doi:10.1264/jsme2.2001.67. Archived from the original on 2009-01-13. Retrieved 2008-06-23.
  7. Costerton JW, Lewandowski Z, Caldwell DE, Korber DR, Lappin-Scott HM (1995). "Microbial biofilms". Annu. Rev. Microbiol. 49: 711–45. doi:10.1146/annurev.mi.49.100195.003431. PMID 8561477.
  8. Urbano P, Urbano F (May 2007). "Nanobacteria: Facts or Fancies?". PLoS Pathog. 3 (5): e55. doi:10.1371/journal.ppat.0030055. PMC 1876495. PMID 17530922.
  9. Kajander EO (June 2006). "Nanobacteria--propagating calcifying nanoparticles". Lett. Appl. Microbiol. 42 (6): 549–52. doi:10.1111/j.1472-765X.2006.01945.x. PMID 16706890.
  10. Raoult D, Drancourt M, Azza S, et al. (February 2008). "Nanobacteria Are Mineralo Fetuin Complexes". PLoS Pathog. 4 (2): e41. doi:10.1371/journal.ppat.0040041. PMC 2242841. PMID 18282102.
  11. Martel J, Young JD (April 2008). "Purported nanobacteria in human blood as calcium carbonate nanoparticles". Proc. Natl. Acad. Sci. U.S.A. 105 (14): 5549–54. doi:10.1073/pnas.0711744105. PMC 2291092. PMID 18385376.
  12. Sahin, Nurettin; Gonzalez, Juan M.; Iizuka, Takashi; Hill, Janet E. (1 June 2010). "Characterization of two aerobic ultramicrobacteria isolated from urban soil and a description of Oxalicibacterium solurbis sp. nov". FEMS Microbiology Letters. 307 (1): 25–29. doi:10.1111/j.1574-6968.2010.01954.x. PMID 20370834.


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