Visit the main page of the Mars section for other information on the topic of life on Mars. This page is one among many pieces of my general argument that there is life on Mars.
Maybe this is not so widely accepted...
Anatoli Pavlov and his colleagues from the Ioffe Physico-Technical Institute in St Petersburg has announced in September 2002 that he concluded that the Deinococcus radiodurans microbe, that can withstand huge doses of radiation, could have evolved this ability on the harsher environment of Mars. The microbe could then have travelled to Earth on pieces of rock that were blasted into space by an impacting asteroid and fell to Earth as meteorites.
He said that it would take far longer than life has existed on Earth for the microbe to evolve that ability in Earth's clement conditions.
Deinococcus radiodurans is renowned for its resistance to radiation - it can survive several thousand times the lethal dose for humans. To investigate how the trait might have evolved, his team tried to induce this radioactivity resistance in the well know E. coli bacteria. They blasted E. coli with enough gamma rays to kill 99.9 per cent of them, let the survivors recover, and then repeated the process. During the first cycle just a hundredth of the lethal human dose was enough to wipe out 99.9 per cent of the bacteria, but after 44 cycles it took 50 times that initial level to kill the same proportion.
However, the researchers calculate that it would take thousands of such cycles before the E. coli were as hardy as Deinococcus. And on Earth it would take between a million and a hundred million years to accumulate each dose, during which time the microbe would have to be dormant. Since life originated on Earth about 3.8 billion years ago, Pavlov does not believe that there has been enough time for this resistance to evolve.
On Mars, however, the researchers calculate that dormant microbes could receive the necessary dose in just a few hundred thousand years, because radiation levels there are much higher.
Moreover, they point out that Mars wobbles on its rotation axis, producing a regular cycle of climate swings that would drive bacteria into dormancy for long enough to accumulate such doses, before higher temperatures enabled the survivors to recover and multiply. Pavlov reported the results in September 2002 at the Second European Workshop on Astrobiology in Graz, Austria.
David Morrison of NASA's Astrobiology Institute is sceptical that Deinococcus came from Mars, arguing that its genome looks similar to those of other Earthly bacteria. But he admits that there's still no obvious explanation for the microbe's resistance to radiation.
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"Deinococcus radiodurans is the most radiation-resistant organism known. Deinococcus radiodurans were discovered in 1956 by Arthur W. Anderson at Oregon Agricultural Experiment Station in Corvallis. Among the many characteristics of Deinococcus radiodurans, a few of the most noteworthy include an extreme resistance to genotoxic chemicals, oxidative damage, high levels of ionizing and ultraviolet radiation, and dehydration." [Ref.1] Top right: Deinococcus radiodurans growing on a nutrient agar plate. The red color is due to carotenoid pigment. Credit: M. Daly, Uniformed Services University of the Health Sciences. Bottom right: Deinococcus radiodurans. |
 
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Most extremophiles have optimized themselves for one or two extreme conditions corresponding to precise ecological niches on the Earth like the hot springs of Yosemite. But Deinococcus radiodurans is more than that: it has been dubbed a polyextremophile because it can endure many extremes, including the most dangerous space hazard.
In 1956, scientists experimenting with radiation to kill bacteria and preserve food for long periods found that something kept growing back after treatment. This was highly unexpected, and this is how this unique microbe was found, and the reason it was studied. Its genetic code has been fully listed.
Later Deinococcus radiodurans has been developped as a special model for bioremediation to clean radioactive supersites left over from the Cold War. Some of those sites contain radioactive materials that are not easily removed by other microbes. While some other bacteria are being genetically engineered to thrive in toxic conditions while converting hazardous waste into reusable effluent, none can resist radiation the way Deinococcus radiodurans can. It then entered The Guinness Book of World Records as the world's most resistant bacteria.
At the Battelle Institute, high-throughput proteomics capability is being demonstrated using Deinococcus radiodurans by Dave Koppenaal, John Wacker, and James Campbell.
So, there are indeed more characteristics than the radioactivity resistance that are consistent with a possible Martian origin of this microbe:
Deinococcus radiodurans can withstand without loss of viability a radiation
levels of five million rads, a dosage that is 3,000 times greater than the lethal dose of 1000 rads
that would kill a human. How? Its genetic code is redundant: it
repeats itself many times so that damage in one area can be recognized and quickly repaired
from one of its backup. A protein, called RecA, matches the shattered pieces of DNA and
splices the correct pieces back together. During these repairs, cell-building activities are shut off and the broken DNA pieces are kept in place.
When exposed to 1.5 million rads of ionizing radiation, Deinococcus repairs the damage to its shattered DNA in a matter of hours.
Deinococcus radiodurans can take 150 breaks for each chromosome without any permanent damage, whereas
E. Coli can only take a maxima of 2 or 3 breaks. Moreover, strong radiation dose
are not mutagene for Deinococcus radiodurans, whereas they are for E. Coli.
Radiation of such magnitude has only existed on earth during the last 50 years, a fraction
of a second in evolutionary time.
The decay of radioactive elements such as uranium in the Martian crust would create high levels of radiation.
On the Earth, there are no natural environments that have fluxes of radiation that could have
favor the evolution of such a powerful resistance to ionizing radiation for this organism.
Deinococcus radiodurans withstands attacks from acid baths. Mars has a large layer of water beneath its surface. On Earth, such groundwater is often acidic. Acidic groundwater dissolves certain kinds of rocks, forming caves. Mars may have these kinds of rocks, resulting in an acidic environment for life. Also, salt layers form when large bodies of salty water evaporate. Mars may have had large bodies of water that have since evaporated, possibly leaving layers of salt.
Deinococcus radiodurans should resist damage from the chemistry of Mars, which chemical experiments done by the labs aboard the two Viking landers indicate may be highly oxidative. Ironically, the highly oxidative chemistry of Mars has been cited by some scientists as a reason that Mars cannot sustain life. But the Martian surface has deposits of a kind of iron oxide called hematite. Hematite is often associated with organisms living in hot springs.
Ultraviolet radiation and charged particles from the sun bombard the surface of Mars, which is
completely unprotected from these kinds of harmful radiation. Actually, some scientists have
suggested that life is impossible on Mars precisely because of this high level of ultraviolet
radiation, and they claim that life has only developped on Earth because our planet is protects
against harmful ultraviolet radiations from the sun by its ozone layer.
But Deinococcus radiodurans withstands attacks from ultraviolet radiation. It is
even the most UV-resistant organism known. It can tolerate something like 10,000 times
the lethal radiation dose for a eukaryotic organism and perhaps 100 times the lethal
dose for most prokaryotic organisms.
Again, it could not have acquire this capability by evolving in a high UV-radiation environment on Earth
because there is and there wasn't no such environment on Earth for a sufficient period of geological time.
On the other end, Mars still has no ozone layer and thus has the high UV-radation environment that would
require its microbes to develop exactly this type of resistance.
Deinococcus radiodurans is resistant to complete dehydration;
many scientists proposed that life cannot exist on Mars because of lack of liquid water
at least on the surface.
It should be reminded that when completely dehydrated, Deinococcus radiodurans is not
less, but more resistant to radiations and extreme temperatures.
Processes in the Martian crust may heat water below the surface, producing pockets of hot
groundwater. The Northern Polar ice cap on Mars is made of water ice. The core of the Southern
Polar ice cap on Mars seems to be made of water ice too. Most of the Martian surface has a layer
of permafrost, soil locked in water ice, beneath it.
The Martian surface has deposits of a kind of iron oxide called hematite, which participates in the
reddishness of the soil. Hematite is often associated with organisms living in hot springs.
On Earth, temperatures as low as 45°C inactivate the bacteria without damaging it.
In 1999, Dr. Robert Richmond, a research biologist at NASA's Marshall Space Flight Center, said [Ref.1]:
"Deinococcus radiodurans beats most of the constraints for survival of life on Mars - radiation, cold, vacuum, dormancy, oxidative damage, and other factors."
The funny part is that with other scientists, he is investigating the possible utility of extremophiles to serve human exploration to inhospitable locations. He plans to use the bacteria in simulated Martian environment devised on Earth to test future life detection experiments for future Mars missions.
Even better, his team actually considers bringing the microbe onto Mars in future missions, for terraformation purpose.
He did seemingly consider that microbe may survive Martian condition because it may be of Martian origin, though.
Battista has rejected that Deinococcus radiodurans could have come to the Earth aboard a meteorite, saying that the meteorite would have been so tremedously hot that any lifeforme would have been killed. But he is not at all a specialist in this matter, and he could not have known at that time that new results on the study of Martian meteorite in October 2000 at Caltech would find out that [Ref.3]:
"Though the study does not directly address the issue of life in meteorites, the authors say the results eliminate a major objection to the panspermia theory -- that any life form reaching Earth by meteorite would have been heat-sterilized during the violent ejection of the rock from its parent planet, or entry into the atmosphere. Prior studies have already shown that a meteorite can enter Earth's atmosphere without its inner material becoming hot."
The same year, Nobel Prize-winning biologist Baruch Blumberg, who is director of NASA's Astrobiology Institute, concluded:
"ALH 84001 has stimulated a remarkable amount of research to test the hypothesis that life exists elsewhere than on Earth. The present study indicates that the temperature inside the meteorite could have allowed life to persist and possibly travel to Earth from Mars."
When David Morrison of NASA's Astrobiology Institute says that he doubts Deinococcus radiodurans came from Mars, he cites that its genome looks similar to those of other Earthly bacteria. But there is no reason yet to claim that life on other planet should not be DNA based, or that its genetic code should be very different than life on Earth. On the contrary, in the notion that it came from Mars, the underlying idea is that panspermia, early cross-contamination of biological material between the two planets is the central idea; and thus, it can obviously be expected that the biological material on Earth and Mars should be very similar.
The same response is elicited by the Deinococcus radiodurans when exposed to dry conditions as it is when exposed to high radiation levels, leading researchers to conclude that the organism evolved to survive long periods of dehydration, and that the resistance to radiation is only incidental to the discovery and development of radiation emitting technology during the second half of this century.
But there are many other microbes on Earth that resist long periods of dehydration and do not at the same time time resist radiation. No other microbe on Earth resists anything near the amount of radiation dose that Deinococcus can accept without damages. Deinococcus is actually quite unique in that aspect.
Usually, microbes that resist radiation and dehydration better than other do so because the form hard capsules called spores. But not D. radiodurans, which does not form a spore.
This enviable talent long puzzled researchers. What evolutionary pressure could have forced Deinococcus radiodurans to develop such repair skills? There are rare cases in which radioactive elements such as uranium or thorium concentrate underground in large amounts, but the radiation fluxes near those sites are still small compared with what the microbe can withstand. Moreover, Deinococcus radiodurans’ oxygen use and other aspects of its metabolism suggest that the bacterium evolved on the surface of the planet, not underground in radiation hot spots.
Said Phil Harriman, Program Director in NSF's Genetics and Nucleic Acids Program in 1996 [Ref.2]:
"There's no apparent reason for such high radiation protection on Earth."
Said Michael J. Daly of the Uniformed Services University of the Health Sciences in Bethesda, Md, 1998:
"There are no natural environments that have fluxes of radiation that could have selected for this organism."
John R. Battista of Louisiana State University in Baton Rouge, recalling his introduction to the microbe in 1988:
"Our conclusion was that D. radiodurans was an organism built upon the ability to survive prolonged periods of desiccation."
But then the researchers unsuccessfully searched a Chilean dry desert for the bacterium, for example. And at the same time, relatives of the microbe have recently been found in areas unlikely to suffer a lack of water, such as hot springs.
Although scientists have documented the existence of extremophiles living in isolated environments like deep-sea hot vents or hotsprings for decades, they have never found an organism that withstands such a wide array of extreme conditions. And this array of extreme conditions correspond to Mars and do not exist on Earth. Deinococcus radiodurans, one of the Earth’s oldest microbe, is probably Martian.
| Species: | Deinococcus radiodurans |
|---|---|
| Species code: | DEIRA |
| Type: | Eubacteria |
| Taxonomy: | Bacteria; Deinococcus-Thermus; Deinococci; Deinococcales;Deinococcaceae; Deinococcus (TaxID : 1299) [NEWT / NCBI] |
| Strain(s): | R1 |
| Genome: | circular, 2.65 Mb + 0.41 Mb; 2 plasmids of 177 Kb and 45 Kb |
| Reference(s): | MEDLINE=20036896 [NCBI, ExPASy, Israel, Japan]; PubMed=10567266; White O., Eisen J.A., Heidelberg J.F., Hickey E.K., Peterson J.D., Dodson R.J., Haft D.H., Gwinn M.L., Nelson W.C., Richardson D.L., Moffat K.S., Qin H., Jiang L., Pamphile W., Crosby M., Shen M., Vamathevan J.J., Lam P., McDonald L., Utterback T., Zalewski C., Makarova K.S., Aravind L., Daly M.J., Minton K.W., Fleischmann R.D., Ketchum K.A., Nelson K.E., Salzberg S., Smith H.O., Venter J.C., Fraser C.M.; "Genome sequence of the radioresistant bacterium Deinococcus radiodurans R1."; Science 286:1571-1577 (1999). |
| Genome official sequence WWW site(s): | http://www.tigr.org/tigr-scripts/CMR2/GenomePage3.spl?database=gdr |
| Other WWW site(s): | GIB (DDBJ) EBI GeneQuiz |
| Description: | Gram-positive, red-pigmented, nonmotile bacterium. It is resistant to ionizing and UV radiation and hydrogen peroxide. It is the most radiation-resistant organism described to date. |
| Properties: | Number of membranes : 1 |
| Presence of a flagella: | ? |
| Number of inteins: | 2 in 2 different sequences |
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