Bacterial Species 2-9-3 Resurrected after a Quarter of a Billion Years

Salt CrystalsAccording to a paper published in the 19 October 2000 issue of the journal Nature, scientists claim to have coaxed bacteria to grow from spores found within salt crystals. If these bacteria were trapped (as spores) when the salt crystals formed, they are 250 million years old.

The spores were located within small pockets of brine contained within the crystals. The bacteria apparently became trapped in the salt deposits as a large salty body of water dried up. As is the case with many bacterial species, the bacteria formed hardy spores to allow them to withstand the dry conditions until such time as things became more hospitable. They had a long wait. The bacteria are of the genus Bacillus and have been assigned the temporary designation of species 2-9-3. Genetic analysis shows these organisms to be related to modern species of Bacillus.

Bacteria have been isolated from ancient samples before - the most notable being spores that were able to germinate after being freed from the gut of a bee encased 25 million-year-old fossilized tree sap - also known as 'amber'. As is the case with all research of this sort, the issue of contamination (by current bacteria) always arises.

The significance of this discovery is the care with which the researchers sought to sterilize all procedures and minimize potential sources of contamination such that it is almost certain that the bacteria that have been grown sprang from spores a quarter of a billion years old.

Sources of potential contamination don't need to be modern either. The salt crystals were found 569 meters below the surface in Carlsbad, New Mexico. It is quite possible that these bacteria may be old, but that they managed to infiltrate these salt crystals well after they formed. By studying the location wherein these crystals were found, and the mineralogy of the crystals themselves, the researchers are certain that once these crystals formed they remained free of subsequent recrystallization or other interaction with external environment.

The implications of this discovery are rather profound - both for the prospects of life upon other worlds - but also for the possibility of life being swapped between worlds.

Martian Life: All Dried Up?

To many scientists, Mars is a world that was once Earth like and likely to have been habitable. Now it is dry and seemingly inhospitable to life. Other researchers are much more optimistic and suspect that life managed to find habitable niches within the planet as it dried out. Indeed, there is a growing interest in the possibility that life might well exist on (or within) Mars today. In the past several decades, the known extent of Earth's biosphere - the portion of our planet that harbors life - has expanded from the outer surface to include regions within our planet. Life has been found in scalding hot hydrothermal vents miles below the sea's surface and miles deep within the rocks that form the Earth's crust.

Recent discoveries by the Mars Global Surveyor show the remnants of what certainly seem to be large ocean basins and the river channels that fed them. This spacecraft has also provided tantalizing evidence that water may be moving through the uppermost regions of Mars' crust today - even bursting out onto the surface on occasion (before sublimating away). Given the temperatures and atmospheric pressure on Mars, a very salty (brine) solution is touted as being the most likely agent at work since it can remain liquid within the cold Martian crust.

The prospect of ancient oceans and current subterranean streams of brine on Mars suggest that the conditions wherein species 2-9-3 lived on Earth were also present on Mars in the past. They also suggest that the conditions whereby species 2-9-3 became entombed on Earth could also have been present.

This doesn't mean that there is life on Mars. However conditions exist on Mars that are similar to ones on Earth wherein life was able to lay dormant for 250 million years. One would expect that Martian salt deposits would now be a high priority for the search for life on Mars.

Were Bacteria the First Astronauts?

ALH84001In August 1996 the world stopped for a moment as the news of possible fossils of Martian life spread. The structures were found within ALH84001, a meteorite found in Antarctica, one of a dozen or so pieces of Mars that were blasted off as the result of a large collision millions of years ago. Pieces of the Moon have also been found on Earth. Subsequent research has shown that such exchanges of rocks between planets are not common - but they are not rare either.

The time required for pieces of Mars to reach Earth can range from thousands to millions of years. Given a solar system 4.5 billion years old - and lots of collisions - it is almost certain that there has been a steady rain of Mars rocks on Earth (and elsewhere). For that matter, shards of planets and moons may well regularly bounce from one world to another.

Indeed, in a system such as the moons orbiting Jupiter (Io, Europa, Ganymede, and Callisto), this may be a common phenomenon - the surfaces of Europa and of the jovian moon Amalthea are thought to be stained by sulfur thrown off of Io by volcanoes.

When the Mars meteorite announcement was made many people asked the next, obvious question: could pieces of Mars bring living organisms to Earth? Assuming that there is life on Mars today (still a TBD) the answer from many scientists was doubtful given the long periods of time required for the rocks to make their way from Mars to Earth. Add in lethal levels of radiation that the rock (and anything in or on it would receive) and it seemed improbable that anything could survive - much less thrive upon arrival. Even if bacteria were encased deep within a rock, the inherent radioactivity of the rock itself would eventually cause a slow motion, but none the less lethal degradation of living systems.

Many species of bacteria enter a stage of dormancy when the external environment becomes less than desirable. In so doing, they restructure themselves, often by forming spores during adverse times so as to be very resistant to external forces - until such time as conditions conducive to normal growth return. Indeed, one could easily classify them as dead since they are more or less inert while dormant. None the less, although dormant, life still flickers enough such that critical genetic machinery and structural proteins are still subject to radiation damage.

There are bacteria on earth that have developed extreme resistance to dry conditions. As a dual benefit, they have also developed a phenomenal ability to resist the deleterious effects of ionizing radiation. In particular, there is the hardy organism Deinococcus radiodurans (lovingly referred to by astrobiologists as "Conan the Bacterium") which can survive a gamma radiation exposure of 1.5 million rads. Such exposures literally blast the organism's DNA apart. Undaunted, Deinococcus radiodurans reforms its entire genome hours later with no apparent ill effects. This organism can also be completely dried out and then be revived and can survive doses of ultraviolet radiation that would kill most other forms of life.

To travel within a rock between one planet and another, taking million or so years to do so - all the while in a bath of radiation, one would need an organism capable of prolonged hibernation or stasis and incredible resistance to radiation. Deinococcus radiodurans is just the right candidate.

Making the perfect bacterial astronaut

species 2-9-3 is a halophile - "salt loving organism" which lives in salt solutions that would be hostile to other forms of life. Were they to have the additional radiation resistant capabilities of Deinococcus radiodurans, they'd make ideal candidates for something called "panspermia" i.e the spreading of life from one world to another via space.

Given the fact that there are known terrestrial bacteria that live happily in nuclear reactors, around deep sea thermal vents, within rocks miles beneath the Earth's surface, inside airplane fuel tanks, and on the surface of spacecraft hardware in a hard vacuum on the lunar surface, the probability that a bacterial species with both traits (radiation resistance and extreme hibernation capabilities) is not at all improbable.

Bacteria and other microorganisms are rather promiscuous and swap genetic traits all the time. Indeed, watching the rate at which they have already evolved resistance to most of the 20th century's antibiotics ought to be a clue to their inherent resiliency and collective ingenuity. One ought to assume that life elsewhere would be similarly capable.

A recent paper published in Nature describes the analysis of the genome of Thermoplasma acidophilum, a primitive organism classified as a thermoacidophilic archaeon (lives in hot acidic environments) thought to resemble some of the earliest forms of life on Earth. A close analysis of one portion of its genome shows substantial similarities to Sulfolobus solfataricus, an organism which lives in the same environment (coal refuse piles and solfatara fields) but not at all related to Thermoplasma acidophilum. The authors suggest that this was part of an adaptive process to extreme environments.

Consider that the radioresistance of Deinococcus radiodurans is a byproduct of its evolutionary adaptation to surviving very dry conditions, and that the ability of species 2-9-3 to survive for vast stretches of time is also an adaptation that allows survival through long dry periods. It is not much of a stretch to suggest that life forms with both extreme radioresistance and the ability to remain dormant for hundreds of millions of years could arise.

Were such a life form to be laying dormant in a rock that had the good fortune to be blasted off of a planet by a large impact event, the stage would be set for a trip elsewhere - perhaps from Mars to Earth. If the rock was of sufficient size, its interior could remain rather cool as it entered the Earth's atmosphere. Were it to land, fracture, and land in a suitable environment, the dormant bacteria within would be ready to grow again.

Again, this is just conjecture - there are a large number of "ifs" in this scenario.

Did it happen?

Has life been swapped between Mars and Earth? DNA may hold the answer. Depending on when it happened, a look at the genomes of Terrestrial and putative Martian life forms would likely answer the question. Were there to be a similar genetic system and similar genetic sequences, the answer would probably be yes. If the genetic systems were different, then the answer would probably be no. But we can't be certain. Life could have been sent from one world to another only to die out after a while. Given the physics of ejected materials from a planetary surface, it is more likely that rocks from a small world like Mars would be sent to Earth than the other way around - but two way swaps are not impossible. During the early history of the solar system, during a period of intense bombardment, Mars was a more habitable planet than was Earth. It is not inconceivable that life originated - and took hold - on Mars before it managed to do so on Earth.

Perhaps Mars seeded Earth with life. Maybe we're Martians after all. Who knows. We're just going to have to go to Mars and find out.

Panspermia: Life Spreads

Panspermia - loosely translated - means 'spreading seeds widely' - in this case between planets, perhaps between stars. Until recently, it was thought that such a notion was improbable given that life couldn't survive even the shortest trip. Now, it would seem, we have homegrown candidates for the task.

panspermiaOf course, just because one assembles circumstantial evidence to show that something is possible, it does not mean that it has actually happened. As humans, we often focus on examining things we know to be possible to the exclusion of that which is improbable or impossible. Yet, what was once yesterday's improbable or impossible event often becomes today's possibility. Now that we have demonstrated that life could be tossed between worlds, perhaps we'll be taking a second look to see if it has happened in our solar system. And if it has happened here ....

Voyager 1 and 2 will come within 1.5 light years or so of the star AC+ 79 3888, an M4 class red dwarf, which will be 3 or so light years from Earth in 40,000 years - far less than 1% of the demonstrated survival time of species 2-9-3. The cumulative radiation exposure should be within the ability of Deinococcus radiodurans to cope.

This may be a slight leap, but should an organism with the radiation hardiness of Deinococcus radiodurans and the ability to remain dormant but viable expressed by species 2-9-3 have been placed aboard the Voyager spacecraft, we'd have a biological envoy capable of viable reproduction across distances of hundreds of light years over time spans measured in millions of years.

The speed at which life throws itself against barren terrain on Earth - be it the aftermath of Mt. St. Helens or volcanic islands erupting out of the sea near Iceland - should be a lesson worthy of potential extraterrestrial applicability.

On Earth, life has shown itself increasingly capable of surviving wherever the laws of physics say that it can - even if it clashes with human preconceptions of what a 'habitable abode" for life is.

Life spreads - wherever it can. Hint: get used to the idea.


Related Links

  • 19 October 2000: Isolation of a 250 million-year-old halotolerant bacterium from a primary salt crystal, Nature (subscription fee required for access)

    "Here we report the isolation and growth of a previously unrecognized spore-forming bacterium (Bacillus species, designated 2-9-3) from a brine inclusion within a 250 million-year-old salt crystal from the Permian Salado Formation. Complete gene sequences of the 16S ribosomal DNA show that the organism is part of the lineage of Bacillus marismortui and Virgibacillus pantothenticus."

  • 19 October 2000: Microbiology: A case of bacterial immortality?, Nature (subscription fee required for access)

    "The potential implications are profound. For instance, can spores effectively be immortal? What is the biochemistry that allows them to survive for so long? Where else on Earth, and to what depths, might ancient bacterial life be lurking? And, given this startling example of apparent bacterial durability, do spores in rocks even provide a mechanism for life to be transported between planets by 'panspermia', as has been proposed?"

  • 18 October 2000: Scientists Revive Ancient Bacteria, AP, Yahoo

    "In what sounds like something out of "Jurassic Park,'' bacteria that lived before the dinosaurs and survived Earth's biggest mass extinction have been reawakened after a 250-million-year sleep in a salt crystal, scientists say."

  • 28 September 2000: The genome sequence of the thermoacidophilic scavenger Thermoplasma acidophilum, Nature (subscription fee required for access)

    "... evidence indicates that there has been much lateral gene transfer between Thermoplasma and Sulfolobus solfataricus, a phylogenetically distant crenarchaeon inhabiting the same environment. At least 252 open reading frames, including a complete protein degradation pathway and various transport proteins, resemble Sulfolobus proteins most closely..."

    "... Although it has been observed previously that in prokaryotes core information processing generally tracks organism phylogeny, whereas metabolism is strongly affected by lateral transfer, it is highly unusual to see such a large number of genes transferred between two phylogenetically distant organisms. We propose that the adaptation to an extreme environment shared by few other organisms has led to substantial genetic exchange."

    Background Information

  • 19 November 1999: Bacteria: the Ideal Astronauts?, SpaceRef
  • Radiation Resistance, SpaceRef Directory
  • Panspermia Resources, SpaceRef Directory
  • Voyager Project, NASA JPL


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