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Structures found on meteorite fragment ALH84001

Nanobacteria is the name of a proposed class of living organisms; specifically cell-walled microorganisms with a size much smaller than the generally accepted lower limit size for life (about 200 nanometres for bacteria). Originally based on observed nano-scale structures in geological formations (including some meteorites), the status of nanobacteria is controversial: some researchers suggest they are a new class of living organisms ^[1][2] capable of incorporating radiolabeled uridine,^[3] while other investigators attribute to them a simpler, abiotic nature.^[4][5]

The term 'calcifying nanoparticles' (CNPs) has also been used as a conservative name regarding their possible status as a life form. The most recent research tends to agree that these structures exist, and probably replicate in some way, but their status as living entities is still hotly debated. In medicine, they have been implicated in the formation of both kidney stones and arterial plaque.

1981-2000

In 1981 Torella and Morita described very small cells called ultramicrobacteria. Defined as being smaller than 300 nm, by 1982 MacDonell and Hood found that some could pass through a 200 nm membrane. Early in 1989, geologist Robert L. Folk found what he later identified as nannobacteria (written with double "n"), that is, nanoparticles isolated from geological specimens^[6] in travertine from hot springs of Viterbo, Italy. Initially searching for a bacterial cause for travertine deposition, scanning electron microscope examination of the mineral where no bacteria were detectable revealed extremely small objects which appeared to be biological. His first oral presentation elicited what he called "mostly a stony silence", at the 1992 Geological Society of America's annual convention.^[7] He proposed that nanobacteria are the principal agents of precipitation of all minerals and crystals on Earth formed in liquid water, that they also cause all oxidation of metals, and that they are abundant in many biological specimens.

Nanobacterium sanguineum was proposed in 1998 as an explanation of certain kinds of pathologic calcification (apatite in kidney stones) by Finnish researcher Olavi Kajander and Turkish researcher Neva Ciftcioglu, working at the University of Kuopio in Finland. According to the researchers the particles self-replicated in microbiological culture, and the researchers further reported having identified DNA in these structures by staining.^[8]

A paper published in 2000 by a team led by an NIH scientist John Cisar further tested these ideas. It stated that what had previously been described as "self-replication" was a form of crystalline growth. The only DNA detected in his specimens was identified as coming from the bacteria Phyllobacterium mysinacearum, which is a common contaminant in PCR reactions.^[4]

Kajander and Ciftcioglu set up a company in Finland in 2000, Nanobac Oy, to market medical diagnostic kits for identifying nanobacteria to medical researchers, and develop prescription medical treatments for calcification-associated diseases. The company was absorbed in 2003 by Nanobac Pharmaceuticals, Inc., a publicly traded company in Tampa, Florida founded by nanobiotic developer Gary Mezo.

2001–present

In 2004 a Mayo Clinic team led by Franklin Cockerill, John Lieske, and Virginia M. Miller, reports to have isolated nanobacteria in diseased human arteries and kidney stones. Their results were published in 2004 and 2006 respectively.^[9][10] Similar findings were obtained in 2005 by László Puskás at the DNA Lab, University of Szeged, Hungary. Dr. Puskás identified these particles in cultures obtained from human atherosclerotic aortic walls and blood samples of atherosclerotic patients but the group was unable to detect DNA in these samples.^[11]

In 2005, Ciftcioglu and her research team at NASA used a rotating cell culture flask, which simulates some aspects of low-gravity conditions, to culture nanobacteria suspected of rapidly forming kidney stones in astronauts. In this environment, they were found to multiply five times faster than in normal Earth gravity. The study concluded that nanobacteria might have a potential role in forming kidney stones and may need to be screened for in crews pre-flight.^[12]

The February 2008 PLoS Pathogens article focused on the comprehensive characterization of nanobacteria. The authors say that their results rule out the existence of nanobacteria as living entities, instead revealing that they are a unique self-propagating entity similar to prions and that they are self-propagating mineral-fetuin complexes.^[13]

An April 2008 PNAS article also reported blood nanobacteria are not living organisms and stated that "CaCO₃ precipitates prepared in vitro are remarkably similar to purported nanobacteria in terms of their uniformly sized, membrane-delineated vesicular shapes, with cellular division-like formations and aggregations in the form of colonies."^[14] The growth of such "biomorphic" inorganic precipitates was studied in detail in a 2009 Science paper, which showed that unusual crystal growth mechanisms can produce witherite precipitates from barium chloride and silica solutions that closely resemble primitive organisms.^[15] The authors commented on the close resemblance of these crystals to putative nanobacteria, stating that their results showed that evidence for life cannot rest on morphology alone.

See also

• ALH_84001 — Mars meteorite found in Antarctica that might contain evidence for microscopic fossils of Martian nanobacteria
• Mimivirus — largest known virus
• Mycoplasma genitalium, Pelagibacter ubique — some of the smallest known bacteria
• Nanoarchaeum — smallest known archaeum
• Nanobe — possible nano-organism first observed in 1996
• Parvovirus — smallest known family of viruses
• Prions — also controversial when first proposed in 1982

References

Additional reading

• Nanobacteria: Facts or Fancies?
• From Scum, Perhaps the Tiniest Form of Life, NY Times December 23, 2006
• Abstract: American Journal Physiology — Heart and Circulatory Physiology May 13, 2004
• Cisar JO, Xu DQ, Thompson J, Swaim W, Hu L, Kopecko DJ (October 2000). "An alternative interpretation of nanobacteria-induced biomineralization". Proc. Natl. Acad. Sci. U.S.A. 97 (21): 11511–5. doi:10.1073/pnas.97.21.11511. PMID 11027350. PMC 17231. http://www.pnas.org/cgi/content/full/97/21/11511.  
• Are Nanobacteria Making Us Ill?, Wired News, Mar. 14, 2005
• Claim made for new form of life, BBC News, May 19, 2004
• Miller VM, Rodgers G, Charlesworth JA, et al. (September 2004). "Evidence of nanobacterial-like structures in calcified human arteries and cardiac valves". Am. J. Physiol. Heart Circ. Physiol. 287 (3): H1115–24. doi:10.1152/ajpheart.00075.2004. PMID 15142839.  
• Infectious Microorganism Linked to Kidney Stones and other Diseases, February 2005
• Nannobacteria Research Page of the Department of Geosciences, Mississippi State University
• Kajander EO, Ciftçioglu N (July 1998). "Nanobacteria: an alternative mechanism for pathogenic intra- and extracellular calcification and stone formation". Proc. Natl. Acad. Sci. U.S.A. 95 (14): 8274–9. doi:10.1073/pnas.95.14.8274. PMID 9653177. PMC 20966. http://www.pnas.org/cgi/content/full/95/14/8274.  
• New Scientist article about nanobacteria
• The Calcium Bomb — The Nanobacteria Link to Heart Disease and Cancer
• Taylor, Michael (1999). Dark Life. New York, NY: Scribner. ISBN 0-684-84191-6.  
• The Time Travelers Academy, a science fiction novel; it tells a story about the nanobacteria found in Martian meteorites.
• Nannobacteria Research associated with Robert Folk.