- Doctors claim to have uncovered new evidence that the
tiny particles known as "nannobacteria" are indeed alive and
may cause a range of human illnesses.
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- The existence of nannobacteria is one of the most controversial
of scientific questions - some experts claim they are simply too small
to be life forms.
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- But US scientists report they have now isolated these
cell-like structures in tissue from diseased human arteries.
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- Their research is described in the American Journal of
Physiology.
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- The team, led by Dr John Lieske at the Mayo Clinic in
Rochester, conducted an analysis of calcified and non-calcified arteries,
arterial plaques and heart valves collected as surgical waste from two
US hospitals.
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- In the lab, they stained the specimens and examined them
under a high power electron microscope.
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- The team found tiny spheres ranging in size from 30-100
nanometres (nm - billionths of a metre), which is smaller even than many
viruses.
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- When the tissue was broken up, filtered to remove anything
more than 200nm and the filtrate added to a sterile medium, the optical
density - or cloudiness - of the medium increased.
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- This, the researchers argue, means the nanoparticles
were multiplying of their own accord.
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- "I think we've taken a systematic approach to evaluating
the participation of these potential nanoparticles, nannobacteria - whatever
you want to call them - in human disease processes," co-author Dr
Virginia Miller, also of Mayo Clinic told BBC News Online.
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- Spheres of influence
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- The particles are also recognised by a dye for DNA and
absorbed uridine, a key chemical component of RNA, which the researchers
argue is evidence the particles are constantly synthesising nucleic acids.
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- Viewed with electron microscopy, the particles also appeared
to have cell walls.
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- The nano-scale objects showed up in tissue from patients
with calcified arterial aneurysms but not uncalcified samples.
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- Nannobacteria have been implicated by some scientists
in the formation of kidney stones and psammona bodies - calcified (mineralised)
structures in ovarian cancer.
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- But many other scientists dispute that they are actually
life forms.
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- "I don't see any convincing evidence for nannobacteria
or DNA [in this study]," Dr John Cisar, of the National Institutes
of Health in Bethesda, US, told BBC News Online.
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- "If you know you're dealing with a life form, you
can use the staining techniques [they used]. But there are false positives
in these types of techniques."
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- Dr Cisar said in research he had conducted, nanoparticles
had tested positive with a stain for nucleic acids. But when he and his
team tried to extract these nucleic acids, none had been found.
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- Previous research carried out by Jack Maniloff of the
University of Rochester in New York has shown that to contain the DNA and
proteins it needs to function, a cell must be a minimum of 140nm across.
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- "One of the questions we always get back is: 'well,
how do you know it's alive if it doesn't have a unique DNA sequence?' This
is true," Dr Miller explained.
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- "But if you go back to how we defined life prior
to our knowing about DNA, our criteria was that things multiplied in culture.
This is what we have."
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- In 1996, nannobacteria came to the attention of the world's
media when scientists announced they had found fossils in a Martian meteorite
of what appeared to be nano-sized bacteria.
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- Scientists are now involved in efforts to isolate DNA
from the nanoparticles. Dr Miller said it was also important to investigate
their role in other diseases.
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- The research is also reported in this week's New Scientist
magazine.
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- © BBC MMIV http://news.bbc.co.uk/2/hi/science/nature/3729487.stm
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