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February 17, 2009 — The genome of a marine
bacterium living 2,500 meters below the ocean's surface is providing
clues to how life adapts in extreme thermal and chemical gradients,
according to an article published Feb. 6 in the journal PLoS Genetics.
The research focused on the bacterium Nautilia profundicola, a
microbe that survives near deep-sea hydrothermal vents. Microorganisms
that thrive at these geysers on the sea floor must adapt to
fluctuations in temperature and oxygen levels, ranging from the hot,
sulfide- and heavy metal-laden plume at the vents' outlets to cold
seawater in the surrounding region.
The study combined genome analysis with physiological and ecological
observations to investigate the importance of one gene in N.
profundicola. That gene, called rgy, allows the bacterium to
manufacture a protein called reverse gyrase when it encounters
extremely hot fluids from the Earth's interior.
Previous studies found the gene only in microorganisms growing in
temperatures greater than 80°C, but N. profundicola thrives best at
much lower temperatures.
"The gene's presence in N. profundicola suggests that it might play
a role in the bacterium's ability to survive rapid and frequent
temperature fluctuations in its environment," said Assistant Professor
of Marine Biosciences Barbara Campbell, the study's lead scientist.
Additional University of Delaware contributors were Professor of
Marine Biosciences Stephen Craig Cary, Assistant Professor of Marine
Biosciences Thomas Hanson, and Julie Smith, marine biosciences doctoral
student. Also collaborating on the project were researchers from the
Davis and Riverside campuses of the University of California; the
University of Louisville; the University of Waikato in Hamilton, New
Zealand; and the J. Craig Venter Institute in Rockville, Md.
The researchers also uncovered further adaptations to the vent
environment, including genes necessary for growth and sensing
environmental conditions, and a new route for nitrate assimilation
related to how other bacteria use ammonia as an energy source.
Photosynthesis cannot occur in the hydrothermal vents' dark
environment, where hot, toxic fluids oozing from below the seafloor
combine with cold seawater at very high pressures.
These results help to explain how microbes survive near the vents,
where conditions are thought to resemble those found on early Earth.
Nautilia profundicola contains all the genes necessary for life in
conditions widely believed to mimic those in our planet's early
biosphere and could aid in understanding of how life evolved.
"It will be an important model system," Campbell said, "for understanding early microbial life on Earth."
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