Projects: LIFE Experiment: Shuttle & Phobos
Bacteria: The "terrifying berry" and the rods from JPL
by Amir Alexander
|
Bacillus safensis
Credit: James Kulleck/NASA/JPL
|
Our LIFE biomodule carries eukaryotea,
archaea, and also contains four types of bacteria.
Bacillus safensis
One hardy type of bacteria selected for the journey to space is
the Bacillus
safensis,
a bacteria of the "bacillus," or "rod shaped" variety.
This bacterium was discovered only a few years ago and in an unlikely location – the
Spacecraft Assembly Facility (SAF) at the Jet Propulsion Laboratory (JPL)
in Pasadena. At the time of the discovery the Mars Odyssey spacecraft was
being assembled in a clean room at SAF, to make sure that the orbiter would
not carry with it any Earthly organisms to the Red Planet. But despite
the thorough cleansing of the assembly area, and despite elaborate procedures
to avoid contamination from the scientists and engineers, colonies of bacteria
were still found on surfaces of the spacecraft, the floor, and other locations
in the clean room. This bacteria, which had survived and even thrived in
the hostile clean room environment, was found to be a new type of bacillus
and it was christened Bacillus safensis, Latin for "bacillus
of SAF."
The secret to Bacillus safensis' remarkable capacity for survival lies in its ability to produce spores when subjected to hostile environmental conditions. Spores, more formally called endospores, are tough internal structures formed within a bacterial cell and containing a copy of the organism's DNA. Unlike spores in eukaryotes, which are often used in reproduction, the purpose of bacterial spores is pure survival. Being inert and possessing a tough external shell, spores are much harder to kill off than the cells that produced them. Even as the functioning parts of the bacterial cells are destroyed, the spores remain, protecting and preserving the organism's genetic material. When external conditions improve, the spores reactivate and grow new functioning bacterial cells.
Deinococcus radiodurans
Another bacteria selected for the long journey to Mars thanks to its remarkable
capacity for survival is called "Deinococcus radiodurans," which is Latin for "terrifying berry that survives radiation." As
its name suggests this bacteria is not rod shaped but round, and it is extraordinarily
resistant to radiation. To get an idea of just how resistant, consider that
a dose of 10 Gy (Grays) of radiation is sufficient to kill a human, and 60
Gy will kill all cells in a culture of the common bacteria E. Coli. But a
culture of Deinococcus radiodurans will fully survive a dose of
5000 (five thousand) Gy, and over a third of the cells will survive a dose
of 15,000 Gy! It is this startling capacity to emerge intact from
the most trying ordeals that earned Deinococcus radiodurans its
popular nickname "Conan the Bacterium."
Unlike B. safensis, D. radiodurans does not produce spores to protect its DNA. A concentrated burst of radiation can introduce hundreds of breaks in its DNA, just as it would in any other organism. This would easily kill ordinary bacteria, but D. radiodurans possesses a secret weapon: a highly sophisticated DNA-repair system. For starters, this "terrifying" bacteria carries not one, but multiple copies of its genome. When its chromosomes are damaged by radiation it uses undamaged portions of the genome copies as templates to repair and recreate the DNA strands. Within 12-24 hours the process is completed and the bacteria culture is fully recovered.
D. radiodurans and its death-defying ability to survive radiation have been known to scientists since 1956, when A. W. Anderson and colleagues were conducting experiments on food-sterilization at the Agricultural Experiment Station in Corvallis, Oregon. Anderson exposed canned meet to a dose of gamma radiation that was strong enough to kill all known life forms. Despite the treatment, however, the meat spoiled, and was found to contain a previously unknown bacteria that had survived the gamma-ray bombardment. Anderson named it Deinococcus radiodurans.
Bacillus subtilis
If B. safensis and D. radiodurans were selected for the
LIFE experiment thanks to their ability to survive under extraordinary circumstances,
another bacteria, Bacillus subtilis,
was picked for a different reason: it is a "model organism," a standard bacteria used over and over again in all kinds of biological experiments. This, said Warmflash, means that "more
is known about B. subtilis than about any other Gram-positive bacteria
(Gram "positive" or "negative" classification refers
to whether a species of bacteria can be dyed by certain standard methods.) "B. subtilis," Warmflash added, "is
the gold standard of Gram-positive bacteria, just as E. coli is
the gold-standard of Gram-negative bacteria."
Bacillus subtilis
Credit: Neal Chamberlain/ASM Microlibrary
|
B. subtilis, nevertheless, is a very tough organism. Like B. safensis it is a spore-producing bacteria and is therefore capable of surviving long periods of exposure to extremes of heat, acidity, and salinity. Two distinct species of B. subtilis will fly in the LIFE canister, one designated "168," the other "MW01." Both are radiation resistant, with MW01 even far more radiation resistant than its cousin 168. Most importantly, B. subtilis was included in the two Biostack experiments that flew on board Apollo 16 and 17 and in a variety of subsequent experiments in low Earth orbit. This means that the effects on the bacteria of LIFE's 34-month sojourn in interplanetary space can be compared with effects of the much shorter journeys to the Moon and back in the early 1970's and to multi-year exposure in low Earth orbit.
Read more about the archaea and eukaryotea in the LIFE biomodule.
|
[ what is this? ]