2010-04-09 11:19:02
Charles Q. Choi
LiveScience Contributor
LiveScience.com charles Q. Choi
livescience Contributor
livescience.com Thu Apr 8, 8:30 am ET
Animals that live without oxygen have been discovered for the first time, deep
under the Mediterranean Sea.
A wide variety of single-celled organisms that live anaerobically, or without
oxygen, had been found in the past, usually deep underwater or deep
underground. But researchers had not found a multi-cellular or metazoan animal
that did so until now - the giant tube worms that live by hydrothermal vents,
for instance, rely on dissolved oxygen.
In the past decade or so, researcher Roberto Danovaro at the Polytechnic
University of Marche in Ancona, Italy, and his colleagues conducted three
expeditions off the south coast of Greece looking for signs of life in samples
of mud from deep, hyper-salty basins in the Mediterranean Sea more than 10,000
feet (3,250 meters) deep. These basins are completely anoxic, or oxygen-free,
and loaded with toxic levels of sulfides.
In these extremes, the investigators were only expecting to see viruses,
bacteria and other microbes. The bodies of multi-cellular animals had
previously been discovered in these sediments, "but were thought to have sunk
there from upper, oxygenated, waters," explained Danovaro.
Instead, "our results indicate that the animals we recovered were alive,"
Danovaro said. "Some, in fact, also contained eggs."
These creatures, which measure less than 1 millimeter long, are known as
loriciferans. They somewhat resemble jellyfish sprouting from a conical shell.
Electron microscopy revealed the three new species of loriciferans the
researchers discovered lack mitochondria, the energy-making organelles or
components in our cells that allow us to generate energy from oxygen among
other functions. Instead, they possess large numbers of organelles resembling
hydrogenosomes - anaerobic forms of mitochondria - that were previously seen in
single-celled organisms inhabiting no-oxygen environments.
These new animals could shed light on what life might have looked like before
the rise of oxygen levels in the deep ocean and the appearance of the first
large animals in the fossil record roughly 550 million to 600 million years
ago, the scientists noted.
The implications of this discovery might also reach far beyond the
Mediterranean Sea, explained biological oceanographer Lisa Levin of the Scripps
Institution of Oceanography in San Diego, who did not take part in this
research.
This new, unexpected finding "offers the tantalizing promise of metazoan life
in other anoxic settings - for example, in the subsurface ocean beneath
hydrothermal vents, or subduction zones, or in other anoxic basins," Levin
said, referring to the subduction zones where one slab of Earth called a
tectonic plate dives beneath another and sometimes leads to earthquakes.
"Good places to look might be the Cariaco Basin and the Black Sea, as well as
the many borderland basins off southern California and Baja California."
"Are there metazoans on other planets with atmospheres different from our own?"
Levin added. "Our ability to answer this question would be strengthened
considerably by more intensive studies of animal-microbe interactions in
extreme settings of our own inner space - the deep ocean."
Danovaro and his colleagues detailed their findings online April 6 in the
journal BMC Biology.