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Until now, scientists thought that only extremophiles—organisms adapted to seemingly intolerable environments—could exist in intense conditions such as those present at high-pressure, high-temperature oceanic hydrothermal vents or in the ice sheets of Antarctica. Anurag Sharma, James Scott, and colleagues at the Geophysical Laboratory (GL) conducted a study that proves otherwise. In fact, their study shows that even common bacteria can live under high-pressure conditions equivalent to those at about 50 km beneath the Earth’s crust or about 160 km under a hypothetical sea. These results expand our notion of where life might be found within the solar system. The February 22, 2002, issue of Science published the paper, and the media, including National Public Radio, the Washington Post, the New York Times, and MSNBC reported on the findings. Sharma, an experimental geochemist and Scott, a microbiologist, are both members of NASA’s Astrobiology Institute (NAI). In a new procedure, the scientists adapted the tools of high-pressure physics to microbiology by using diamond-anvil cells to subject two bacteria species—E. coli, commonly found in the human gut, and the metal-reducing Shewanella oneidensis—to pressures of up to 16,000 times the pressure found at sea level.“This is a very high-pressure condition for biology,” says Sharma.“Since liquid water turns into a solid high-pressure ice even at room temperature, these conditions are typically considered inhospitable.” Both E. coli and Shewanella use formate in their metabolic processes in the absence of oxygen. With molecular spectroscopy, the scientists measured the microbes’ use of formate to determine their metabolic rates. They confirmed their viability with optical observations on stained bacteria and found that they can survive pressures far beyond those of deep ocean trenches and in the deep crust. The new techniques open the door for the “real time” examination of pressure and temperature effects on microbial communities. According to Scott, “One of the fundamental questions that need to be asked now is whether the bacteria’s response is due to adaptation or selection. Our results raise important questions about the impact of pressure on the evolution of life, and the study has tremendous impact on understanding a number of processes that are due to phase shifts caused by environmental conditions, such as the use of methane hydrates by microorganisms.” The study suggests that as far as pressure goes, the subduction zones on Earth and deep water/ice structures, such as those found on the moons Europa, Callisto, and Ganymede, might be environments that could harbor life. The techniques being developed at GL will be used to test various hypotheses on the viability and probability of life in different environments—even before any NASA missions for the search for life are planned. For some time evidence has been mounting that a large portion, if not most, of living organisms today exist in the deep subsurface of Earth—including deep frozen lakes and the ice caps. This and other recent findings can now be taken into account when looking for life elsewhere. “Soon the only thing that should limit our investigation of the survivability of life on Earth and beyond is our imagination,” concludes Scott. For more information see: http://www.gl.ciw.edu/~sharma/microbe/microbe.html |