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Nanobacterium ( , pl. nanobacteria ) is the unit or member name of a former proposed class of living , specifically cell wall microorganisms, now discredited, with a size much smaller than the generally accepted lower limit for life (about 200 nanometer for bacteria, like mycoplasma). Originally based on observed nano-scale structures in geological formations (including the Martian meteorite Allan Hills 84001), the status of nanobacteria was controversial, with some researchers suggesting they are a new class of living organism capable of incorporating radiolabeled uridine, and others attributing to them a simpler, abiotic nature. One skeptic dubbed them "the cold fusion of microbiology", in reference to a notorious episode of supposed erroneous science.Jack Maniloff, quoted in "The Rise and Fall of Nanobacteria", Young and Martel, Scientific American, January 2010 The term "calcifying " (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. 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."The Rise and Fall of Nanobacteria", Young and Martel, Scientific American, January 2010
In 1996, NASA scientist David McKay published a study suggesting the existence of nanofossils — fossils of Martian nanobacteria — in ALH84001, a meteorite originating from Mars and found in Antarctica.
Nanobacterium sanguineum was proposed in 1998 as an explanation of certain kinds of pathologic calcification (apatite in ) by Finland researcher Olavi Kajander and Turkey researcher Neva Çiftçioğlu, working at the University of Kuopio in Finland. According to the researchers, the particles Self-replication in microbiological culture, and the researchers further reported having identified DNA in these structures by staining.
A paper published in 2000 by a team led by 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 myrsinacearum, which is a common contaminant in PCR reactions.
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 potentially have a role in forming kidney stones and may need to be screened for in crews pre-flight.
An article published to the PLOS 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 as Life entities and that they are instead a unique Self-replication entity, namely self-propagating mineral-fetuin complexes.
An article published to the PNAS (PNAS) in April 2008 also reported that 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." 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. 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.
Further work on the importance of nanobacteria in geology by R. L. Folk and colleagues includes study of calcium carbonate Bahama ooids,Folk, RL and Lynch. FL (2001) Organic matter, putative nanobacteria and the formation of oolites and hard grounds, Sedimentology, 48:215–229. Silicate mineral clay minerals,Folk, RL and Lynch, FL, (1997) The possible role of nanobacteria (dwarf bacteria) in clay-mineral diagenesis, Journal of Sedimentary Research, 67:583–589. Sulfide minerals,Folk, RL (2005) nanobacteria and the formation of framboidal pyrite, Journal Earth System Science, 114:369–374 and iron oxides.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. In all of these chemically diverse minerals, the putative nanobacteria are approximately the same size, mainly 0.05–0.2 μm. This suggests a Common descent. At least for the type locality at Viterbo, Italy, the biogenicity of these minute cells has been supported by transmission electron microscopy (TEM).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. Slices through a green bioslime showed entities 0.09–0.4 μm in diameter with definite cell walls and interior dots resembling ribosomes, and even smaller objects with cell walls and interiors with diameters of 0.05 μm.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. Culturable organisms on earth are the same 0.05 μm size as the supposed nanobacteria on Mars.Folk, RL and Taylor, L (2002) nanobacterial alteration of pyroxenes in Martian meteorite ALH84001, Meteorology and Planetary Science, v. 37:1057–1070.
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