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Nanobe

Structures found in the ALH84001 meteorite are similar to the structures found in nanobes
Not to be confused with Nanobacteria or Ultramicrobacteria.

A nanobe (/ˈnænoʊb, ˈneɪnoʊb/)[1] is a tiny filamental structure first found in some rocks and sediments. Some scientists hypothesize that nanobes are the smallest form of life, ⁠1/ 10 ⁠ the size of the smallest known bacteria.[2]

No conclusive evidence exists that these structures are, or are not, living organisms, so their classification is controversial.

The 1996 discovery of nanobes was published in 1998[3] by Uwins et al.,[4] from the University of Queensland, Australia. They were found growing from rock samples (both full-diameter and sidewall cores) of Jurassic and Triassic sandstones, originally retrieved from an unspecified number of oil exploration wells off Australia's west coast. Depths of retrieval were between 3,400 metres (2.1 mi) and 5,100 metres (3.2 mi) below the sea bed. While Uwins et al.[3] present assertions against it, they do not exclude the possibility that the nanobes are from a surface contaminant, not from the rock units cited.

The smallest are just 20 nanometers in diameter. Some researchers believe that these structures are crystal growths, but the staining of these structures with dyes that bind to DNA might indicate that they are living organisms.[5]

They are similar to the structures found in ALH84001, a Mars meteorite found in the Antarctic. A 2022 study concluded that ALH84001 did not contain Martian life; the discovered organic molecules were found to be associated with abiotic processes (ie, "serpentinization and carbonation reactions that occurred during the aqueous alteration of basalt rock by hydrothermal fluids") produced on the very early Mars four billion years ago instead.[6][7]

Nanobes are similar in size to nanobacteria, which are also structures that had been proposed to be extremely small living organisms. However, these two should not be confused: Nanobacteria were thought to be cellular organisms, while nanobes are hypothesized (by some) to be a previously unknown form of life or protocells.[citation needed]

Claims

  • It is a living organism (contains DNA or some analogue, and reproduces).
  • Has a morphology similar to Actinomycetes and fungi.
  • Nanobes are about 20 nm in diameter, which may be too small to contain the basic elements for an organism to exist (DNA, ribosomes, etc.), suggesting that if they grow and reproduce they would need to do so in an unconventional way.
  • The Martian meteorite ALH84001, discovered in 1984 in the Antarctic, contained similar tubular structures which some astrobiologists suggested could be evidence of life at an earlier time on Mars.[8]

Responses

A review in Microbes and Environments[9] of the various ultra-small forms of proposed life states that the main criticism of nanobes is that they appear too small to contain the biochemical machinery needed to sustain life. The review also states that there is no evidence that nanobes are organisms in themselves and not fragments of larger organisms.

Tony Taylor was one of the authors of the original nanobe paper.[3] He argues that the conspicuous lack of phosphorus in the X-ray spectroscopy data and the failure to find DNA using various DNA amplification techniques demonstrates that nanobes do not have any DNA or RNA. He also argues that they may have a completely different mechanism for heredity, which would account for many of their unusual chemical and physical properties.

Size scale context

Sizes of micro-organisms and infectious agents
Agent Description Size
(nm)
Pithovirus largest known virus 1,500 nm
Pandoravirus  one of the largest known viruses 1,000 nm
Nanoarchaeum  smallest known archaeum  400 nm
Mycoplasma smallest known bacterium 300 nm
Nanobacteria former proposed class of lifeforms smaller than bacteria < 200 nm
Parvovirus smallest known viruses 18–28 nm
Nanobes hypothetical lifeforms smaller than viruses ≈20 nm
Prion smallest known infectious agent (protein) ≈10 nm

See also

References

  1. ^ "nanobe". Lexico U.S. English Dictionary. Oxford University Press. Archived from the original on 31 July 2019.
  2. ^ Nanjundiah, V. (2000). "The smallest form of life yet?" (PDF). Journal of Biosciences. 25 (1): 9–10. doi:10.1007/BF02985175. PMID 10824192. S2CID 29030837.
  3. ^ a b c Uwins, Philippa J.R.; et al. (1998). "Novel nano-organisms from Australian sandstones" (PDF). American Mineralogist. 83 (11–12): 1541–1550, Part 2. Bibcode:1998AmMin..83.1541U. doi:10.2138/am-1998-11-1242.
  4. ^ "Nanobes: About Philippa Uwins and the discovery team". microscopy-uk.org.uk.
  5. ^ "Nanobacteria and nanobes – Are they alive?". Carlton.edu. Science Education Resource Center. Northfield, MN: Carlton College.
  6. ^ Dunn, Marcia (13 January 2022). "Study nixes Mars life in meteorite found in Antarctica". apnews.com. Associated Press. Retrieved 13 January 2022.
  7. ^ Steele, A.; et al. (13 January 2022). "Organic synthesis associated with serpentinization and carbonation on early Mars". Science. 375 (6577): 172–177. Bibcode:2022Sci...375..172S. doi:10.1126/science.abg7905. PMID 35025630. S2CID 245933224.
  8. ^ McSween, H. Y. (1997). "Evidence for life in a martian meteorite?". GSA Today. 7 (7): 1–7. PMID 11541665.
  9. ^ 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. Retrieved 23 June 2008.
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