Earth microbes on the moon
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What could be worse for would-be space travelers than a catastrophic breach in their protective spacesuits, the high-tech, multilayered fabric blanket that balloons under the pressure of a life-saving flow of oxygen and insulates against the frozen harshness of deep-space vacuum?
But for some kinds of microbes, the harshness of space travel is not unlike their everyday stressful existence, the successful execution of ingenious survival tricks learned over billions of years of Earth-bound evolution.
Click the image at right for a synopsis (below) of astrobiology at NASA's Marshall Space Flight Center.
Space historians will recall that the journey to the stars has more than one life form on its passenger list: the names of a dozen Apollo astronauts who walked on the moon and one inadvertent stowaway, a common bacteria, Streptococcus mitis, the only known survivor of unprotected space travel. As Marshall astronomers and biologists met recently to discuss biological limits to life on Earth, the question of how an Earth bacteria could survive in a vacuum without nutrients, water and radiation protection was less speculative than might first be imagined. A little more than a month before the forthcoming millennium celebration, NASA will mark without fanfare the thirty year anniversary of documenting a microbe's first successful journey from Earth.
In 1991, as Apollo 12 Commander Pete Conrad reviewed the transcripts of his conversations relayed from the moon back to Earth, the significance of the only known microbial survivor of harsh interplanetary travel struck him as profound:
"I always thought the most significant thing that we ever found on the whole...Moon was that little bacteria who came back and lived and nobody ever said [anything] about it."
Left, Above: Astronaut Pete Conrad (photographed by crew mate Alan Bean) inspects Surveyor 3's camera assembly. Surveyor 3 landed on the moon on April 20, 1967, at 2.94° S, 23.34° W in Oceanus Procellarum.On Nov. 12, 1969, Conrad and Bean piloted the Apollo 12 Lunar Module (background) to a landing 156 m (512 ft) away.
Although the space-faring microbe was described in a 1970 Newsweek article, along with features in Sky and Telescope and Aviation Week and Space Technology, the significance of a living organism surviving for nearly three years in the harsh lunar environment may only now be placed in perspective, after three decades of the biological revolution in understanding life and its favored conditions.
As the lunar voyagers answered a similar question more than a century ago, in Jules Verne's classic, From the Earth to the Moon: "To those who maintain that the planets are not inhabited one may reply: You might be perfectly in the right, if you could only show that the earth is the best possible world."
The remarkable lunar survivor from Apollo 12 thus gives scientific pause.
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Three decades, the biological revolution
To a biologist, freeze-drying microbes for harsh space travel conjures up rather mundane kitchen science, a simple reenactment of how a yeast packet taken from the freezer can make bread dough rise prior to baking. But to a new breed of biologist exploring the harshest conditions on Earth, how a delicate microbe manages to counteract vacuum, boiling temperatures, burning radiation, and crushing pressures deep in the frozen icecaps is the study of life itself.
Left: Interior view of Surveyor 3 TV camera; surviving microorganisms cultured from the polyurethane foam insulation (1 mL) covering the circuit boards (upper left).
The Deep Sleep
The Surveyor probes were the first U.S. spacecraft to land safely on the Moon. In November, 1969, the Surveyor 3 spacecraft's microorganisms were recovered from inside its camera that was brought back to Earth under sterile conditions by the Apollo 12 crew.
The 50-100 organisms survived launch, space vacuum, 3 years of radiation exposure, deep-freeze at an average temperature of only 20 degrees above absolute zero, and no nutrient, water or energy source. (The United States landed 5 Surveyors on the Moon; Surveyor 3 was the only one of the Surveyors visited by any of the six Apollo landings. No other life forms were found in soil samples retrieved by the Apollo missions or by two Soviet unmanned sampling missions, although amino acids - not necessarily of biological origin - were found in soil retrieved by the Apollo astronauts.)
How this remarkable feat was accomplished only by Strep. bacteria remains speculative, but it does recall that even our present Earth does not always look as environmentally friendly as it might have 4 billion years ago when bacteria first appeared on this planet.
May 1995: Deciphering of the first complete gene of a living organism (1,749 genes of the Hemophilus influenzae bacteria). In the New York Times, Nobel Laureate and co-discoverer of the DNA double helix, James Watson said: "I think it's a great moment in science."
September 1995: Deciphering of the smallest known viable genome on the planet, Mycoplasma genitalium, giving the first genetic script of what separates life from non-life
July 1996: Deciphering of the first genome from the third "super kingdom" of life, the Archea, and the organism Methanococcus jannaschii, a deep-sea hot vent microbe, separating bacteria and eukaryotes (such as plants and animals)
1997: Deciphering the genome of the human pathogen, Helicobacter pylori, the ulcer-causing bacteria that dwells in the stomachs of half of the people on Earth
1998: Deciphering the entire microbial genome of the cause of Lyme disease, Borrelia burgdorferi
1998: Deciphering the entire microbial genome of the sulfur-metabolizing Archea, Archaeoglobus fulgidus, the industrial cause of "souring" oil wells
1998: Deciphering the microbial genome, Deinococcus radiodurans, having the remarkable capacity to withstand massive space-scale doses of over 1.5 million rads of radiation--3,000 times the dose that would kill a human in space
Culture plate from Surveyor 3 camera foam sample (1 cc volume of polyurethane foam). Samples of the microorganism (left) were sent to the US Communicable Disease Center at Atlanta, Georgia, which confirmed it as Streptococcus mitis. a common harmless bacteria from the nose, mouth and throat in humans.
The Streptococcus genus consists of Gram-positive bacteria which appear as chains under microscopic observation. Members of Streptococcus can be aerobic, anaerobic, or microaerophilic. The organisms in this genus are characterized by a coccus appearance, a thick cell wall, and aerobic action on glucose. The Surveyor foam sample was cultured in bacterial media (Thioglycollate) at 37 C. The facultative streptococci are the largest group of bacteria isolated from the oral cavity. They comprise almost 50% of the organisms isolated from plaque and the gingival sulcus. This most abundant oral streptococci are the alpha-hemolytic (Viridans) streptococci, which are part of the normal flora and symbiotically limit the growth of competing harmful bacteria in the mouth.
It has been calculated that the normal human houses about a trillion bacteria on the skin, 10 billion in the mouth, and 100 trillion in the gastrointestinal tract. The latter number is far in excess of the number of eukaryotic cells in all organs which comprise the human host. It is sometimes said quite simply that there is more of "them" than "you'' in you. The normal flora occupy available colonization sites which makes it more difficult for other microorganisms (nonindigenous species) to become established.
Left: Streptococcus genus, bacterial cells
Extremophiles: Life on the Edge
The Earth looked remarkably different when bacteria first colonized the oceans and land. Oxygen was scarce. To many early plants, cyanobacteria and anaerobic bacteria, oxygen was a poison. The thin ozone layer that currently shields intense solar radiation was largely unformed. Bacteria, originating under global conditions very different from our present day, can be thought to be space travelers already: over time the generational records of microbes have sampled swings in environment here on earth that rival the differences between today's Earth and some of the more hospitable planetary outposts. The growing list of space-hardiness conditions include:
Vacuum conditions, with bacteria taken down to near zero pressure and temperature, provided suitable care is exercised in the experimental conditions.
Pressure, with viable bacteria after exposure to pressures as high as 10 tonnes per square centimeter (71 tons/sq-in). Colonies of anaerobic bacteria have recently been recovered from depths of 7 km (4.2 mi) or more in the Earth's crust.
Heat. Archaebacteria that can withstand extreme heat have been found thriving in deep-sea hydrothermal vents and in oil reservoirs a mile underground
Radiation, including viable bacteria recovered from the interior of an operating nuclear reactor. In comparison to space, each square meter on Earth is protected by about 10 tons of shielding atmosphere.
Long preservation, including bacteria revived and cultured after some 25 million years of encapsulation in the guts of a resin-trapped bee.
"I should venture to assert, that if these worlds are habitable, they either are, have been, or will be inhabited."
Jules Verne, From the Earth to the Moon, 1877.
The streptococcus bacteria on Surveyor 3 might not be the only interplanetary microbial hitchhikers. In 1996, researchers at NASA's Johnson Space Center announced that they had found evidence of microfossils in a Mars meteorite recovered from a field of blue ice in the Antarctic.
The presence of polycyclic aromatic hydrocarbon [PAH] molecules in the Allan Hills meteorite was taken as one sign that objects in the rock are microfossils. Critics claim that the PAHs are contamination from the ice.
The recent discovery of a 13th meteorite, apparently from Mars, might help is resolving the issue.
"The fact that it was found in the Sahara means that it can't possibly be contaminated with PAHs from ice," said Richard Hoover, an X-ray astronomer at NASA's Marshall Space Flight Center.
Hoover is part of two investigations that will develop tools and techniques to prepare and examine specimens that may have life forms. He also is planning a trip to Antarctica to look for samples of life thriving under extreme conditions.
"We don't know how long this 13th rock has been in the Sahara," Hoover said, "but finding another SNC [Mars meteorite] is a very exciting result."
While long associated with rocket propulsion, NASA's Marshall Space Flight Center also is deeply involved in space science research. Recently, this has expanded to include astrobiology, the study of life outside the Earth. In addition to Hoover's work, Dr. David Noever, author of this article, is developing a "D'Arcy machine," a program to help computers recognize life forms in electron microscope and other images.
NASA's mission is divided into four enterprises: Earth Science, Space Science, Aeronautics and Space Transportation Technology, and Human Exploration and the Development of Space (HEDS). Marshall Space Flight Center is the designated lead center for microgravity research, under the Human Exploration and Development of Space (HEDS) enterprise in the 1998 NASA Strategic Plan. This directive answers two important scientific questions:
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More science headlines - NASA space science research
Space physics for the third millennium - education series
A program to help computers recognize life forms in electron microscope and other images is in development; headline from June 11, 1998.
Two investigations that will develop tools and techniques to prepare and examine specimens that may have life forms; headline from May 22, 1998.
Bacteria can survive unlikely changes of environment, including the growing list of space-hardiness conditions; headline from March 5, 1998.
Allan Hills meteorite home page - Johnson Space Center
Astrobiology - NASA Ames Research Center
NASA's 1998 Strategic Plan - important missions and scientific goals
Planetary protection and exobiology - Mars 98 exploration team at JPL
Planetary Protection and Mars Sample Return were covered in an Ames Research Center workshop in 1997.
The NASA Strategic Plan of the Human Exploration and Development of Space Enterprise
These links from CyberChemics, Inc
- Scouting for Life: Prospects for our solar system
- Educator's guide to preserving bacteria
- Apollo 12 excerpt from the Lunar Surface Journal
- List of citations and related reading
- How the Surveyor 3 bacteria might have survived the moon trip
Space Settlement - artist's renderings of space colonization (America On Line)
Reston Communications has:
- Astrobiology Website
- The Whole Mars Catalog Life on Mars web site links to lots of resources.
The National Research Council offers:
- Mars Sample Return: Issues and Recommendations
- Scientific Assessment of NASA's Mars Sample-Return Mission
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Author: David Noever
Curator: Linda Porter
NASA Official: Gregory S. Wilson