MadSci Network: Microbiology

Re: do nanobacteria exist in nature?

Date: Thu Mar 31 10:10:49 2005
Posted By: Michael Weaver, Staff, Biology/Microbiology, Merck & Co., Inc.
Area of science: Microbiology
ID: 1111677196.Mi


Nanobacteria definitely exist and they have been found on earth in such places as human and cow blood. Researchers E. Olavi Kajander and his colleagues from the University of Kuopio in Finland have even been able to culture them in bovine (cow) serum. These researchers also believe that they grow in urine and may be the cause of most kidney stones. Nanobacteria are thought to be the smallest cell-walled bacteria. Depending on the environment they live in they can vary dramatically in size. Under unfavorable conditions they form very large multi-cellular units, but they can release much smaller particles, some of which are only 50 nm in size (smaller than many viruses) when the conditions are not so favorable. Although metabolic rates of nanobacteria are very slow, they can produce carbonate apatite on their cell envelope mineralizing rapidly most of the available calcium and phosphate. This is why the researchers believe that they may be the cause of most kidney stones.

Nanobacteria belong to, or may be ancestors of, the alpha-2 subgroup of Proteobacteria. They may still partially rely on primordial life- strategies, in which minerals and metal atoms associated with membranes played catalytic and structural roles reducing the number of enzymes and structural proteins needed for life. In other words, they use the external environment to do a lot of the work that most bacteria perform inside their own cells. This allows them to be much smaller than most bacteria since their cells do not have to house all of the normal machinery of life. They simply don't need all that extra space. This simplistic life strategy may also explain the ability of this life-form to survive in extreme environmental conditions and their very slow growth rates (10000 times slower than E. coli!).

However, the name nanobacteria is highly controversial as you may have discovered. The controversial nature of the name nanobacteria swirls around its previous use with the slight difference in spelling— nannobacteria—by Robert L. Folk, a geologist at the University of Texas at Austin. For almost two decades, Folk has riled microbiologists by claiming that bumps and knobs that he sees in electron microscope pictures of soils and rocks represent bacteria with diameters as small as 10 nanometers.

According to Folk, such nannobacteria are widespread and plentiful, and by precipitating various minerals, they may have had a major impact on geology. His speculations gained greater notoriety in 1996 with the discussion of possible evidence of extraterrestrial life in a meteorite from Mars. One group of scientists suggested that the so-called microfossils detected in that meteorite resemble Folk's nannobacteria.

Many microbiologists, however, argue that Folk offers no compelling evidence that his bumps and knobs are alive. These scientists remain intensely skeptical that bacteria that small can exist. "The Folk stuff really stretches the theoretical limits. . . . It doesn't just stretch them, it denies them," says Kenneth H. Nealson, a microbiologist at the NASA's Jet Propulsion Laboratory in Pasadena, Calif.

While bacteria generally have diameters of a micrometer (1000 nm) or more, biologists have for many years recognized the existence of tinier bacteria, whose diameters range from 50 to 200 nm. Below such sizes, Nealson and others claim, there's simply not enough room to contain the machinery of life as we know it.

Even a bacterium 50 nm in diameter—the smallest that Kajander describes— would be jam-packed, assuming its cell walls were about 10 nm thick and the microbe contained DNA and even one protein-making ribosome, which is 25 nm in diameter. "At 50 nm, one could imagine that things could stay alive. When you get much smaller than that, it's really hard to imagine," says Nealson.

Here is a link to a site that you might help you better understand the current research surrounding nanobacteria:


Travis, John. Science News, Vol. 154, No. 5, August 1, 1998, p. 75.

Kajander, E.O., and N. Çiftçioglu. 1998. Nanobacteria: An alternative mechanism for pathogenic intra- and extracellular calcification and stone formation. Proceedings of the National Academy of Sciences 95(July 7):8274.

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