Microbes beneath sea floor genetically distinct
Tiny microbes beneath the sea floor, distinct from life on the Earth's
surface, may account for one-tenth of the Earth's living biomass, according
to an interdisciplinary team of researchers, but many of these minute
creatures are living on a geologic timescale.
"Our first study, back in 2006, made some estimates that the cells could
double every 100 to 2,000 years," says Jennifer F. Biddle, PhD. recipient in
biochemistry and former postdoctoral fellow in geosciences, Penn State. "Now
we have the first comprehensive look at the genetic makeup of these
microbes." Biddle is now a postdoctoral associate at the University of North
Carolina, Chapel Hill.
The researchers looked at sediment samples from a variety of depths taken
off the coast of Peru at Ocean Drilling Site 1229. They report their
findings in today's (July 22) online issue of the Proceedings of the
National Academy of Sciences.
"The Peruvian Margin is one of the most active surface waters in the world
and lots of organic matter is continuously being deposited there," says
Christopher H. House, associate professor of geoscience. "We are interested
in how the microbial world differs in the subsea floor from that in the
surface waters."
The researchers used a metagenomic approach to determine the types of
microbes residing in the sediment 3 feet, 53 feet, 105 feet and 164 feet
beneath the ocean floor. The use of the metagenomics, where bulk samples of
sediment are sequences without separation, allows recognition of unknown
organism and determination of the composition of the ecosystem.
"The results show that this subsurface environment is the most unique
environment yet studied metagenomic approach known today," says House. "The
world does look very different below the sediment surface." He notes that a
small number of buried genetic fragments exist from the water above, but
that a large portion of the microbes found are distinct and adapted to their
dark and quiet world.
The researchers, who included Biddle; House; Stephan C. Schuster, associate
professor; and Jean E. Brenchley, professor, biochemistry and molecular
biology, Penn State; and Sorel Fitz-Gibbon, assistant research molecular
biologist at the Center for Astrobiology, UCLA, found that a large
percentage of the microbes were Archaea, single-celled organisms that look
like Bacteria but are different on the metabolic and genetic levels. The
percentage of Archaea increases with depth so that at 164 feet below the sea
floor, perhaps 90 percent of the microbes are Archaea. The total number of
organisms decreases with depth, but there are lots of cells, perhaps as many
as 1,600 million cells in each cubic inch.
" These microbes influence the Earth's long-term carbon cycle and also these
microbes may be quite ancient," says Biddle.
If the rest of the world is like the Peruvian Margin, then at least one
tenth and as much as a third of the Earth's biomass could be these tiny
microbes living in the mud. However, this population lives at an unusual
rate. Single-celled organisms usually consume food for energy and then
rather than grow larger, simply divide and reproduce themselves. While the
Bacteria Escherichia Coli, as an example, doubles its numbers every 20
minutes, these Archaea double on the order of hundreds or thousands of years
and consume very little energy.
"In essence, these microbes are almost, practically dead by our normal
standards," says House. "They metabolize a little, but not much."
According to House, organisms metabolizing at such slow rates is what we
could expect to find in other areas of our solar system because such
environments have much less energy available than on Earth. Perhaps, similar
organisms may be in hydrothermal vents beneath the ice of Europa -- the
second moon of Jupiter -- or in subsurface aquifers of Mars.
"We do not expect the microbes in other places to be these microbes
exactly," says House. "But, they could be living at a similar slow rate."
Biddle notes that these microbes could survive major Earth impacts by
asteroids, so the subsea floor could be a refuge for life during extinction
events. Now this study shows they may be a reservoir of novel genetic
material as well. Her future research will focus on understanding the
lifestyle of the microbes.
"For example, how do they die?" asks Biddle. "It is a simple question that
we cannot answer."
Source: Penn
Statehttp://www.physorg.com/news135878602.html
Posted by
Robert Karl Stonjek
