Posted on 09/26/2002 3:12:44 PM PDT by Heartlander
Tough Earth bug may be from Mars
19:00 25 September 02
Exclusive from New Scientist Print Edition
A hardy microbe that can withstand huge doses of radiation could have evolved this ability on Mars.
That is the conclusion of Russian scientists who say it would take far longer than life has existed here for the bug to evolve that ability in Earth's clement conditions. They suggest the harsher environment of Mars makes it a more likely birthplace.
The hardy bugs could have traveled to Earth on pieces of rock that were blasted into space by an impacting asteroid and fell to Earth as meteorites.
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, Anatoli Pavlov and his colleagues from the Ioffe Physico-Technical Institute in St Petersburg tried to induce it in E. coli.
99.9 per cent deadly
They blasted the bugs 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 bugs 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.
Dormant bugs
On Mars, however, the researchers calculate that dormant bugs could receive the necessary dose in just a few hundred thousand years, because radiation levels there are much higher.
What is more, they point out that the Red Planet 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 last week at the Second European Workshop on Astrobiology in Graz, Austria.
David Morrison of NASA's Astrobiology Institute is sceptical that Deinococcus came from Mars, pointing out that its genome looks similar to those of other Earthly bacteria. But he admits that there's still no obvious explanation for the bug's resistance to radiation.
"It is certainly a mystery how this trait has developed and why it persists," he says.
-Stuart Clark
Other stuff:
Spider mite upsets evolutionary theory
If the past is any guide, something like this:
"So what? The bugs didn't turn into gerbils, did they?"
Silly. That's precisely the point of the statement in the article.
Other stuff:
Spider mite upsets evolutionary theory
Haploid sexual species. Interesting.
What does 50 times one one hundredth come out to?
I'll give you a hint 50 * .01 = 0.5. Their numbers don't hunt.
Most definitely NOT evolution. The researchers contaminated their samples somehow. (/sarcasm)
" In fact, [bacteria] had mobilized the genetic defenses that now defeat penicillin millions of years before humans discovered the drug. The findings challenge the long-standing notion that bacteria's antibiotic-fighting arsenal arose in response to modern antibiotics. "
I wouldn't bet this will change one Darwininian's mind.
I suspect you are stating this in regard to the article? There's selection, but, so far, no indication of mutation. You might not want to quit your day job (defending Bush) just yet.
The penicillin example is commonly bandied about here. I'm sure it will continue unabated.
It's already known that antibiotic resistance is shared between bacteria on plasmids. It's also known that these plasmids have been around for a while. The news here is that the genes have been around for millions of years.
Somehow I find the concept unacceptable that bacteria know that when a human produced penicillin molecule hits them it is time to act.
I'm surprised. It sounds like something right up your alley, natural genetic engineering and all that. Cells which don't contain the plasmid will collect it under selective pressure. It's evolution, nonetheless.
This doesn't prove evolution. This proves that resistance to radiation follows a lognormal distribution (or something close) within a given population. The article doesn't say anything that I see about that ability being passed on to future generations. Only that harsher treatments on the same set of microbes got diminishing results. Interesting, but it is about mortality in a population, not about whether that is passed along ot future generations. That can be hypothesized, but such a hypothesis is not supported by this data.
What do you think 'cycles' means?
I think you missed my point. I don't believe the Penicillium notatum is less than 100 years old.
Ah, OK. Quite right!
What do you think of the numbers?
50 * .01 = 0.5
Are we really more resistant to radiation than the "improved" bug?
I doubt that. Their starting 99.9 lethality rate seems way too high for the radiation dose used. But... the sensitivity variance may be very large.
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