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 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]

Microbacterial studies from Berkeley Labs at UC Berkeley have produced detailed microscopy images of ultra-small microbial species.[6] Cells imaged have an average volume of 0.009 cubic microns, meaning that about 150,000 of them could fit on the tip of a human hair.[6] These bacteria were found in groundwater samples from Rifle, Colorado, after the water was filtered through filters commonly believed to sterilize water.[6] These samples were then brought to Berekeley's Lab's Life Sciences Division, and analyzed with 2-D and 3-D cryogenic transmission electron microscopy. Images of theses ultra-small bacteria display dense spirals of DNA, few ribosomes, hair-like fibrous appendages, and minimized metabolic systems.[6] Such cells probably gain most essential nutrients and metabolites from other bacteria.[6] Genomic sequencing of specimens found the genomes to be about 1 million base pairs long, and that the species found came from multiple phyla.[6] Bacteria in the ultra-small size range are thought to be rather common but difficult to detect. [6]


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] (ie. 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

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. PMID 23156684. S2CID 6391715.
  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. doi:10.1128/AEM.63.4.1382-1388.1997. PMC 168432. PMID 9097435.
  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. doi:10.1128/AEM.41.2.518-527.1981. 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. Krotz, D. (2015). "First Detailed Microscopy Evidence of Bacteria at the Lower Size Limit of Life". Retrieved 2020-05-11.
  7. 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.
  8. 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.
  9. 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.
  10. 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. S2CID 20169194.
  11. 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.
  12. 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.
  13. 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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