Earth's
twilight zone is simply teeming with life - bacteria by the zillions
Even though scientists still argue
about what life is, discoveries made in the past few weeks have
shown that much more of it teems on our planet than previously
thought: organisms are thriving under the ocean floor; in ice
caps; even in orbit miles over our heads.
This kind of life is the most successful on Earth. The number
of people on the planet - a few billion - pales compared with
bacteria, which number 5,000 billion billion billion, a cosmic
total.
They are found anywhere that higher life forms breed including
in our bodies. More bacteria live in our mouths than the number
of people who have ever lived. But they also seem to thrive in
the most forlorn nooks and crannies on Earth, forming a huge twilight
zone of life.
Every time that a bacterium is found grazing in a desolate spot,
whether on a damp rock ndeep underground, in a stratospheric air
current, or wriggling in superheated water near a volcano, scientists
gain confidence that bacteria -or something like them -probably
exist elsewhere in the universe.
People have traditionally been fascinated by the bigger organisms
that walk, crawl and fly around the planet. But they should spare
a thought for the smaller things in life, such as an apparently
insignificant bug with the forgettable name of SAR11
The SAR refers to how the plankton was first identified in the
Sargasso Sea area of the North Atlantic when Prof Stephen Giovannoni
hunted for genes in water samples more than a decade ago. ''SAR11
was the first major group of uncultured bacteria to be discovered
by gene cloning and sequencing techniques, and it has since played
a leading role in the development of microbe hunting methods,''
said Prof Giovannoni, of Oregon State University, Corvallis.
He likens the microbial world to ''an unexplored frontier populated
with species that have never been identified, named or studied
''. A few weeks ago, a new analysis based on samples taken from
across the planet revealed that Prof Giovannoni might have stumbled
upon the most common creature on the planet.
His latest project reveals that
SAR11 may make up more than one third of all bacterial cells in
the ocean surface waters, and almost one fifth of cells in deeper
water. ''They are possibly the smallest cells known, and all together
they weigh about as much as all of the fish in the oceans, ''said
Prof Giovannoni, who reported the find with colleagues from the
University of California ,Santa Barbara, in the journal Nature
.
They are about 1/5000 of a millimetre long and have a volume that
is about one hundredth of that of the common gut bug E coli. The
new measurements of the number of actual SAR11-like cells show
that they make up about half of the microbial community in Atlantic
surface waters.
Globally there may be a vast number
-24,000,000,000,000,000,000,000,000,000 give or take a few, making
them candidates for the most successful creatures on Earth. These
tiny ocean microbes are so small that billions will fit into a
teaspoon; so abundant that, at 200 million metric tons, they may
influence the climate.
''Vast populations of SAR11 increase during the summer and decrease
during the winter, in a cycle that correlates with the build-up
and decline of dissolved organic carbon in the ocean surface,
''said Dr Robert Morris, lead author of the study. This suggests
that SAR11 has an active role in the oceanic carbon cycle, which
affects the concentrations of carbon dioxide in the Earth 's atmosphere
that contribute to global warming.
Under the oceans, another frontier has been discovered that expands
the realm of seemingly hostile environments where organisms can
live. In the light of recent work, the deep ocean crust can now
be viewed as an immense ''biosphere ''of life in its own right
that covers most of the Earth. According to Prof Giovannoni: ''People
have wondered what types of organisms might live within Earth
's crust. This has given us one of the best looks we 've ever
had at that environment.''
In the 3 ·5 million-year-old crust almost 1,000 feet beneath
the bottom of the ocean off the coast of Oregon, Prof Giovannoni
and colleagues found moderately hot water moving through heavily
fractured basalt that was depleted in sulphate and enriched with
ammonium. The discovery suggests biological activity in a high-pressure,
undersea location far from the types of carbon or energy sources
upon which most life on Earth is based.
Instead of digesting organic molecules, as most life does, the
novel bugs appear to dine on inorganic molecules such as sulphide
or hydrogen, and carbon dioxide. The level of biological activity
of these bacteria was sufficiently high that ammonia levels in
the subsurface samples were 142 times higher than those in nearby
sea water.
''This is one of the best views we 've ever had of this difficult-to-reach
location in the Earth 's crust and the life forms that live in
it, ''said co-author Dr Michael Rappe. ''We knew practically nothing
about the biology of areas such as this, but we found about the
same amount of bacteria in that water as you might find in surrounding
sea water in the ocean. It was abundant. As more research such
as this is done, we 'll probably continue to be surprised at just
how far down we can find life within the Earth, and the many different
environments under which it 's able to exist.''
While pressure and depth do not seem to deter bacteria, nor does
extreme cold. Another recent discovery was of 3,000-year-old microbes
in an ice-sealed briny lake in Antarctica. This ancient, unusual
and extreme ecosystem in Lake Vida - among the largest of the
lakes in Antarctica 's McMurdo Dry Valleys -was found about 2,000
miles south of New Zealand by a team led by Prof Peter Doran of
the University of Illinois, Chicago.
The research overturns earlier assumptions that Lake Vida was
frozen solid. Using ground-penetrating radar, ice core analyses
and long-term temperature records, the researchers showed that
Vida has a vast amount of ancient organic material and sediment,
and a cold, super-salty, layer of liquid under about 60ft of ice
-an environment that remains liquid at temperatures below -100C,
well below the freezing point of pure water.
The super-concentrated salt lake has been isolated from the atmosphere
for at least 2,800 years. Carbon-14 dating showed microbes gathered
from ice near the brine to be more than 2,800 years old. Ice core
samples taken from above the pool of brine revealed frozen bacteria
and algae that came back to life after gradual melting.
The chilly brine itself may also harbour living things. To find
out, the National Science Foundation and Nasa are funding a follow-up
study to extract samples.
While bugs have been found deep underground, there is evidence
that they also soar overhead. On January 20, 2001, balloon-borne
sterile ''cryosamplers ''were sent into the stratosphere -at altitudes
of up to 25 miles -by a team led by Prof Jayant Narlikar, director
of the Inter University Centre for Astronomy and Astrophysics
in Pune, with other Indian scientists.
Last year, a team of astronomers and biologists lead by Prof Chandra
Wickramasinghe reported evidence of viable bacteria in air samples
at 25 miles up. The quantities suggested that, worldwide, about
a ton of bacteria is raining down on us each day.Recently, in
the journal FEMS Letters, Dr Milton Wainwright of Sheffield University
reported that he has managed to isolate a fungus and two types
of bacterium from one of the space-derived samples collected at
25 miles.
Given that contamination is not responsible, some believe the
find backs the idea of panspermia, which argues that Earth is
being bombarded by micro-organisms from space. However, sceptics
will argue that the likeliest source of the bugs remains Earth
itself. Even so, the fact that bugs must have made it into orbit
long before humans ranks as a fascinating find.
Roger Highfield
Roger Highfield will talk about
his new book, The Science
of Harry Potter , at the Cheltenham Festival of Science
which starts on June 4. For a brochure, e-mail
[email protected],visit
www.cheltenhamfestivals.co.uk
or call 01242 237377.
The Science of Harry Potter - How Magic Really Works (Headline)
is available for £11 ·99 + £1 ·99 p&p
from Telegraph Books Direct on 0870 155 7222
5 feb
2003


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