Contents

Nanobe

Rock and sediment microstructure

Not to be confused with NanobacteriaorUltramicrobacteria.

Ananobe (/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]}

• 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]

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.

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

• Smallest organisms
• Protocell

• Color photo of a nanobe colony. microscopy-uk.org.uk (photo).
• "Definition of nanobe". microscopy-uk.org.uk.
• "Introduction to nanobes". microscopy-uk.org.uk.
• "Nanobe images and links". microscopy-uk.org.uk.
• "Interview of Philippa Uwins" (transcript). 7.30 Report. Australian Broadcasting Corporation.
• Workshop. Size Limits of Very Small Microorganisms. U.S. National Academies of Sciences.
• Hogan, Jenny (22 May 2004). "Nanobes: A new form of life?". Astrobiology Magazine.
• Broad, William J. (18 January 2000). "Scientists find smallest form of life, if it lives". The New York Times.
• "How small can life be?". nai.nasa.gov. NAI news. National Aeronautics and Space Administration. Archived from the original on 14 June 2009. via "NAI news". Astrobiology.