Nanobacterium (/ˌnænoʊbækˈtɪəriəm/NAN-oh-bak-TEER-ee-əm, pl.nanobacteria/ˌnænoʊbækˈtɪəriə/NAN-oh-bak-TEER-ee-ə) is the unit or member name of a former proposed class of livingorganisms, specificallycell-walledmicroorganisms, now discredited, with a size much smaller than the generally accepted lower limit for life (about 200 nm forbacteria, likemycoplasma). Originally based on observed nano-scale structures in geological formations (including the Martian meteoriteAllan Hills 84001), the status of nanobacteria was controversial, with some researchers suggesting they are a new class of living organism[2][3] capable of incorporating radiolabeleduridine,[4] and others attributing to them a simpler,abiotic nature.[5][6] One skeptic dubbed them "thecold fusion of microbiology", in reference to a notorious episode of supposed erroneous science.[7] The term "calcifyingnanoparticles" (CNPs) has also been used as a conservative name regarding their possible status as a life form.
Research tends to agree that these structures exist, and appear to replicate in some way.[8] However, the idea that they are living entities has now largely been discarded, and the particles are instead thought to be nonliving crystallizations of minerals and organic molecules.[9]
In 1981 Francisco Torella and Richard Y. Morita described very small cells calledultramicrobacteria.[10] Defined as being smaller than 300 nm, by 1982 MacDonell and Hood found that some could pass through a 200 nm membrane[citation needed]. Early in 1989, geologistRobert L. Folk found what he later identified asnannobacteria (written with double "n"), that is, nanoparticles isolated from geological specimens[11] intravertine from hot springs ofViterbo, 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 1992Geological Society of America's annual convention.[12] 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.[12]
In 1996, NASA scientistDavid McKay published a study suggesting the existence of nanofossils — fossils of Martian nanobacteria — inALH84001, a meteorite originating fromMars and found in Antarctica.[13]
A paper published in 2000 by a team led byNIH scientistJohn Cisar further tested these ideas. It stated that what had previously been described as "self-replication" was a form ofcrystalline growth. The only DNA detected in his specimens was identified as coming from the bacteriaPhyllobacterium myrsinacearum, which is a common contaminant inPCR reactions.[5]
In 2004, aMayo Clinic team led by Franklin Cockerill, John Lieske, andVirginia M. Miller reported to have isolated nanobacteria from diseased humanarteries andkidney stones. Their results were published in 2004 and 2006 respectively.[4][15] Similar findings were obtained in 2005 by László Puskás at theUniversity 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.[16]
In 2005, Ciftcioglu and her research team atNASA used a rotatingcell 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 potentially have a role in forming kidney stones and may need to be screened for in crews pre-flight.[17]
An article published to thePublic Library of Science Pathogens (PLOS Pathogens) in February 2008 focused on the comprehensive characterization of nanobacteria. The authors claim that their results rule out the existence of nanobacteria asliving entities and that they are instead a uniqueself-propagating entity, namely self-propagating mineral-fetuin complexes.[18]
An article published to theProceedings of the National Academy of Sciences (PNAS) in April 2008 also reported that blood nanobacteria are not living organisms, and stated that "CaCO3 precipitates preparedin 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."[6] The growth of such "biomorphic" inorganic precipitates was studied in detail in a 2009Science paper, which showed that unusualcrystal growth mechanisms can producewitherite precipitates frombarium chloride andsilica solutions that closely resemble primitive organisms.[19] The authors commented on the close resemblance of these crystals to putative nanobacteria, stating that their results showed that evidence for life cannot rest onmorphology alone.
Further work on the importance of nanobacteria in geology by R. L. Folk and colleagues includes study ofcalcium carbonateBahamaooids,[20]silicateclay minerals,[21]metal sulfides,[22] andiron oxides.[23] In all of these chemically diverse minerals, the putative nanobacteria are approximately the same size, mainly 0.05–0.2 μm. This suggests acommonality of origin.[citation needed] At least for the type locality at Viterbo, Italy, thebiogenicity of these minute cells has been supported bytransmission electron microscopy (TEM).[24] Slices through a green bioslime showed entities 0.09–0.4 μm in diameter with definite cell walls and interior dots resemblingribosomes, and even smaller objects with cell walls andlucent interiors with diameters of 0.05 μm.[25]Culturable organisms on earth are the same 0.05 μm size as the supposed nanobacteria on Mars.[26]
^Ciftcioglu N, Kuronen I, Åkerman K, Hiltunen E, Laukkanen J, Kajander EO (1997). "A new potential threat in antigen and antibody products: Nanobacteria". In Brown F, Burton D, Doherty P, Mekalanos J, Norrby E (eds.).Vaccines 97. Molecular approaches to the control of infectious diseases. New York: Cold Spring Harbor Laboratory Press. pp. 99–103.ISBN0-87969-516-1.
^Ciftcioglu N, McKay D, Mathew G, Kajander E (2006). "Nanobacteria: fact or fiction? Characteristics, detection, and medical importance of novel self-replicating, calcifying nanoparticles".J Investig Med.54 (7):385–94.doi:10.2310/6650.2006.06018.hdl:2060/20060028181.PMID17169260.S2CID35400477.
^abMiller V, Rodgers G, Charlesworth J, Kirkland B, Severson S, Rasmussen T, Yagubyan M, Rodgers J, Cockerill F, Folk R, Rzewuska-Lech E, Kumar V, Farell-Baril G, Lieske J (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.PMID15142839.
^A convention has been adopted between researchers to name -or spell- the nanoparticles isolated from geological specimens asnannobacteria, and those from biological specimens asnanobacteria.
^Folk, RL and Lynch. FL (2001) Organic matter, putative nanobacteria and the formation of oolites and hard grounds, Sedimentology, 48:215–229.
^Folk, RL and Lynch, FL, (1997) The possible role of nanobacteria (dwarf bacteria) in clay-mineral diagenesis, Journal of Sedimentary Research, 67:583–589.
^Folk, RL (2005) nanobacteria and the formation of framboidal pyrite, Journal Earth System Science, 114:369–374
^Folk, RL and Carlin J (2006) Adventures in an iron birdbath: nanostructure of iron oxide and the nanobacteria connection, Geological Society of America, Abstracts with programs, v. 38 (3), p. 6.
^Kirkland, B and Lynch, FL (2005) nanobacteria, Big Foot and the Loch Ness Monster—what are you supposed to believe?, Geological Society of America, abs. with progr., v. 37:253.
^Folk, RL and Kirkland, B, (2007) On the smallness of life: new TEM evidence from biofilm in hot springs, Viterbo, Italy, Geological Society of America, abs. with proper., v. 39 (6) 421.
^Folk, RL and Taylor, L (2002) nanobacterial alteration of pyroxenes in Martian meteorite ALH84001, Meteorology and Planetary Science, v. 37:1057–1070.
