Hardy Microbes Appear Able to Survive in Space |
By Kathy Sawyer
Microbiologist Rocco Mancinelli was at work in tidal flats along the coast of Baja California Sur one day about seven years ago when his research team noticed some interesting hummocks of dried-out, crusted salt. Mancinelli used a hammer to break one open and found inside a green stripe that turned out to be a thriving colony of microorganisms.
Salt is so hostile to most life forms that people have used it for centuries as a preservative. The thought occurred to Mancinelli that the little green salt-lovers, as well as some red ones discovered in a nearby salt company pond gone "bad," would make ideal candidates for exposure to an even more hostile environment – space.
On Sept. 23, 80 samples of the red and green Mexican microbes (species from the archaea genus Haloarcula and the bacteria genus Synechococcus) returned from the third in a series of flights into space as part of the European Space Agency's Biopan experiment. Evidence from the flights, launched on Russian Foton rockets, as well as extensive ground experiments, indicate that, indeed, the microbes are in a minuscule minority of known life forms capable of surviving prolonged exposure to the vacuum of space.
The study of organisms is of more than frivolous interest: It bears on theories about the cosmic pathways that life might follow, such as the possibility that it arose elsewhere and traveled to Earth in chunks of rubble. The topic has taken on added urgency for those who work in the exotic field of planetary protection – that is, preventing biological contamination of Earth by other planets and vice versa.
For the first time since the Apollo program, NASA is preparing to bring home samples from other solar system bodies, including some deemed potentially more hospitable for life than the moon. Mars is the primary target, but among the other candidates are a comet, an asteroid, Jupiter's moon Europa and other major Jovian satellites. At the same time, planetary missions generally are becoming more invasive, raising the potential for reaching bio-friendly environments using subsurface drills, penetrators and robot divers. Expert panels formed by the National Academy of Sciences and a federal interagency task force are issuing recommendations on the issue.
If indeed some microbes might survive in the recesses of spacecraft systems, researchers want to make sure they know how to sterilize the outbound ships effectively. Among other motivations, they consider it imperative that they not export either a complete organism or biological material that could then be "discovered" on another world and misinterpreted as an alien bug.
"We want to ensure that no terrestrial organism makes the round trip" on a sample return mission, said Donald DeVincenzi, a planetary protection official at NASA's Ames Research Center in California. "A positive result like that could cause a lot of confusion . . . a lot of false excitement and all kinds of problems."
A case study from the Apollo 12 mission in 1969 provides a cautionary tale. On the lunar surface, astronauts Pete Conrad and Alan Bean retrieved a camera from the Surveyor robot craft, which had landed almost three years earlier, and carried it back to Earth. Analysts at what is now NASA's Johnson Space Center in Houston concluded that a common Earth bacterium, Streptococcus mitis (found in the human mouth, throat and nose), most likely had flown aboard Surveyor from Earth to the moon and survived years in the vacuum – apparently nestled deep inside the camera in a foam insulation between two circuit boards. No other biological signs were found in any other material returned by Apollo astronauts.
However, the interpretation was disputed from the outset by several scientists, including Martin Favero, a microbiologist who worked for the federal Centers for Disease Control and Prevention in the early 1970s. Favero and colleagues concluded that the camera equipment most likely was contaminated during postflight handling in the Houston lab, and that the microbe had never been to the moon. In a recent interview, Favero said he was "amazed" to learn last year that some scientists were not aware that anyone had challenged the initial interpretation.
Michael Meyer, NASA's chief exobiologist, suspects this scenario could be repeated with the planned Mars sample return. "You can expect a false positive. The question is, what sort of level of false positive can you tolerate without thinking that you've discovered life on another planet?"
A series of startling discoveries in the last two decades has awakened scientists to the amazing resilience and abundance of microscopic life. Terrestrial organisms have been found thriving at extreme temperatures and pressures, in sunless depths of sea and ice, in the interior of a working nuclear reactor. These revelations have made other environments scattered around the solar system seem suddenly promising as nurseries of primitive life. At the same time, the controversy surrounding the famous Martian meteorite ALH 84001 has alerted researchers to the amazing complexities of sorting out subtle microscopic clues to a biological presence.
For most organisms exposed to the harsh conditions of space, however, death has been instantaneous. Mancinelli, of the SETI (Search for Extraterrestrial Intelligence) Institute in California, works with organisms from extreme environments and is one of a tiny number of scientists trying to study the destructive effects of space on living organisms as well as how some survive.
He is collaborating with pioneer Gerda Horneck and her colleagues at the German space organization DLR, who have spent three decades exposing microbes to space. In a classic experiment, Horneck's team in the late 1980s flew spores of Bacillus subtilis – a common, harmless organism found in soil and fresh water – on NASA's Long Duration Exposure Facility (LDEF), a bus-sized spacecraft that stayed in space for six years.
The spores represent a dormant phase of the bacterium's life cycle designed to see it through hard times. The cell shuts down its metabolism and dehydrates itself, the DNA (genetic material) wraps itself in a protective coat, and the whole cell forms an outer armor, making itself fairly resistant to desiccation, heat and the ultraviolet radiation from the sun.
After six years riding in a dry preparation (as opposed to a liquid medium) in open space, Horneck's hardy spores showed an 80 percent survival rate when shielded from radiation – either by at least one other layer of sister spores or a thin layer of glucose and salts. Those exposed to radiation died quickly.
Mancinelli's salt-lovers from Baja, by contrast, are active organisms, not in a specialized resting state. "These organisms I'm working with are not spore-formers," he said. "That's the big deal."
The first flight in 1994 carried just 24 samples, including controls. After two weeks in space, Mancinelli found that 10,000 kilojoules of ultraviolet radiation had destroyed – broken to bits – much of the microbial DNA. But "Lo and behold, we got survival! . . . Just a few percent, but it was significant."
In addition to the recent Biopan flight, Mancinelli has also won a berth on the fledgling International Space Station for a much more detailed microbe experiment. He is testing several hypotheses to explain the organisms' survival. The salt in which they thrive (which has some UV-absorbing properties) and their ability to live with almost no water seem key. "That's what we're trying to figure out: what combination of things allows them to survive," he said.
© 1999 The Washington Post Company