[meteorite-list] Cells' Magnet Bared - Natural Compass Exposes Life On Earth And Beyond

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:53:35 2004
Message-ID: <200212171823.KAA16199_at_zagami.jpl.nasa.gov>

http://www.nature.com/nsu/021216/021216-4.html

Cells' magnets bared

Natural compass exposes life on Earth and beyond.

HELEN PEARSON
Nature Science Update
17 December 2002

Geologists may more accurately assess the state of ancient
Earth - thanks to fossilized bacteria.

Some bugs carry tiny magnetic compasses to help them swim at
a comfortable depth in water. These have been preserved in
rocks up to 2 billion years old. They give clues to prehistoric
Earth's life, magnetic field and climate.

But the magnets in living bacteria have been largely ignored, says
Arash Komeili of the California Institute of Technology in Pasadena.
He and his team are probing the obscure, membrane-bound sacs
called magnetosomes that enclose the tiny crystals.

"We had no idea what states they go through in a bacterium's normal
life cycle," Komeili says. The team has preliminary evidence that the
structures can form and dissolve, he revealed at the American
Society for Cell Biology meeting in San Francisco.

Ultimately, this could help geologists decipher whether ambiguous
fragments of magnetite are signs of early life. Since 1996, for
example, scientists have hotly debated the meaning of bands rich in
magnetite on a martian meteorite, ALH84001.

"Every conceivable non-biological technique has since been
suggested for forming them," says geobiologist Joe Kirschvink, also
at the California Institute of Technology. "By far the simplest
interpretation is that there must have been life on Mars four billion
years ago."

Magnetic deviant

In biological circles, magnetosomes are considered extraordinary.
Textbooks hold that primitive cells, such as bacteria, do not have
compartments called organelles dividing them up. "People just don't
talk about organelles in bacteria," says Komeili.

Some fish also bear cells containing magnetosomes, and scientists
speculate that so, too, might homing animals such as bees, termites
and pigeons.

Komeili hopes to work out whether this level of cell
organization actually evolved in some bacterial cells first. He has
already identified one of the proteins involved in making
magnetosomes. This is related to a protein called actin used in the
architecture of mammalian cells.

"The work could give us some important clues about the evolution of
all higher life-forms on Earth," says Kirschvink. There are many
peculiar biological features of the magnetic bacteria that remind us
"rather strongly" of primitive cells with nuclei, he comments.
Received on Tue 17 Dec 2002 01:23:17 PM PST