If microbial life is found on Mars, will it be native to the planet or something carried there from Earth? Either way, will it be safe to return samples of such organisms to Earth?
Astrobiology, the search for life elsewhere, says a University of Illinois microbiologist, is making us look a lot closer at microbial life on Earth -- how it adapts and its relationship to emerging infectious diseases.
"Even if we don't find life on other planets, we are learning a lot about life on the Earth, particularly microbial life," Abigail Salyers said in an interview about her speech Friday, Feb. 15 at the annual meeting of the American Association for the Advancement of Science in Boston, Mass. She challenged scientists to consider far-reaching possibilities in a talk titled "Are There Medical Implications of Geomicrobiology?"
Salyers, a professor of microbiology in the College of Medicine at the University of Illinois' Urbana-Champaign campus, is the outgoing president of the American Society for Microbiology, the oldest and largest life sciences organization in the world, with more than 42,000 members. Her year as president, she said, has made her "an antenna absorbing the information coming from the members and trying to transmit some sense of it all."
Although the ASM represents 25 disciplines of microbial specialization, she said, there has been in the last five years a blurring of distinctions among them, and an increasing amount of communication. And now, she said, scientists need to focus more about life on Earth as the quest for life "out there" is attracting growing attention.
"The big question for scientists, and which has implications for Earth, is can you have microorganisms evolve that would be able to cause disease in humans, animals or plants in a place where there are no humans, animals and plants?" she said.
Adaptability, Salyers added, "makes the issue a big one for astrobiology as we send spaceships to other planets."
Earth already has yielded examples of the ability of microbes to exist in seemingly harsh and hostile environments, and bacteria normally not associated with disease have turned deadly under unexpected conditions, she said.
Just last month, scientists reported in the journal Science the discovery of bacteria and fungi deep below the ice, in the rocks and soil, of Antarctica. For astrobiologists, Salyers said, this discovery heightens speculation that microbial life could dwell on or under a similar landscape on Mars or in the ice-covered seas of Europa and Ganymede, two of Jupiter's moons. Interestingly, while the early Viking and Mariner space probes were gathering data from Mars in the 1970s, scientists on Earth were discovering bacteria and the Archaea living and thriving in deep-ocean vents and other harshly cold and hot environments, she said.
Could it be, she asked, that previous probes to Mars -- Viking, Mariner and, more recently, the failed Mars Polar Lander -- carried Earth bacteria that survived the cold vacuum and intense radiation exposure of space? "Many microbes are not as fragile as we long thought," she said.
If microbial life is found on Mars, it may be difficult to determine if it began there or was imported from Earth and adapted to the Martian climate, she said.
"Is it possible that we could populate Mars with bacteria from Earth? And if there is life on Mars, would the bacteria we introduce prove to be Mars' version of the Andromeda Strain?" she said, referring to the 1971 movie in which scientists are faced with a deadly alien virus.
On Earth, unexpected adaptations do happen. Salyers noted that:
o In 1976, a mysterious lung-damaging illness to be known as Legionnaires' disease swept through a Philadelphia convention, killing 34 people. The causative bacterium was dubbed Legionella pneumophila, which lives in water. Microbiologists theorize that the bacterium may have adapted to live inside of amoebas, which usually digest and kill bacteria. Instead of dying out, the bacteria simply hitched a ride to a human host.
o Another bacterium, Listeria monocytogenes, which is found in soil and water, often makes its way into food and causes food poisoning. Scientists have discovered that Listeria can survive and multiply even during refrigeration.
o Black-band disease, which has been killing corals in the oceans, "may be caused or exacerbated by cyanobacteria," which normally dwell as part of phytoplankton in the ocean. Salyers was part of a research team, led by UI geologist Bruce Fouke, that reported in December that these bacteria might be teaming with human sewage and shipyard discharge in a way that kills coral under certain conditions.
"In recent years, we've had unpleasant surprises in the form of emerging infectious diseases," Salyers said. "This is a shock. You would think that any organism capable of causing disease would have done so by now. Yet it is clear that there are microorganisms that have not been discovered out there in nature that are capable of causing disease.
"Every time humans do something to benefit human beings, be it surgery, construction or air-conditioning, we create new opportunities for microorganisms to encounter things they have never encountered before," she said. "So, we as scientists must ask, what are the limits. Can we predict an emerging infectious disease before it happens?
"We are hoping that by learning more about what bacteria experience out in nature, we might be able to determine what makes it possible for them to change and cause disease," she said. - By Jim Barlow
[Contact: Jim Barlow]