- Bacteria large enough to be seen with
the naked eye has been discovered deep in ocean sediment off the coast
of Namibia.
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- The balloon-shaped bacteria measure up
to 0.75 millimeter in diameter -- about the size of the period at the end
of this sentence. A typical bacterial cell is about 750 times smaller than
that, making this the largest bacterium ever identified, according to a
study in the latest journal Science.
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- Heide Shulz, a doctoral student at the
Max Planck Institute for Marine Microbiology in Germany, says she knew
the first time she saw the giant bacteria that it had never been identified.
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- But, she says, "I had to convince
people. They didn't quite believe me."
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- Shulz and an international team of researchers
say genetic tests confirm that the bacteria are a new species.
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- The bacterial cells are usually found
connected by mucus into strands that resemble a pearl necklace, prompting
researchers to name them Thiomargarita namibiensis, or "Sulfur Pearl
of Namibia."
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- Also setting these bacteria apart is
an amazing ability to survive conditions that would normally spell instant
death.
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- Like many bacteria, Thiomargarita "breathes"
nitrate, which is found mostly in water above the sediment. But unlike
all but a few related types of nitrate-breathing bacteria, Thiomargarita
"eats" sulfur, and it has to live down in the sediment to find
it.
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- Some bacteria can move up to the sediment's
surface to take a nitrate "breath." Thiomargarita, however, can't
move. Instead, when storms stir up sediment, nitrate is mixed down into
it and the bacteria fill an internal storage compartment -- which takes
up most of the cell's volume -- with nitrate.
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- They use this compartment like a scuba
tank to survive for three months or more without a breath. Other bacteria
would be dead within a day.
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- Thiomargarita can also store sulfur in
the cell area outside the compartment to use as food when none is available.
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- "Thiomargarita has to sit there
and take whatever nature gives it," says Douglas Nelson, a microbial
ecologist at the University of California, Davis. "It's a whole new
adaptive strategy for microorganisms."
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