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Thursday, June 07, 2007

The REAL Superbug

Time for boasting... See, my GF is a doctor, and she works with strongly immuno-depressed patients - actually, she does immuno-depresses them on purpose, by destroying their immune system in the attempt to treat them from Leukemia or other hematological disease.

So, these patients have to be kept in sterile room, where air is micro-(nano?)filtered and such - still some bacteria manage to evade the strict surveillance, then she has to wack them down with robust doses of antibiotics. I asked her how do they manage the emergence of resistant strains, and she answered "with great care" - for every infection, they use the narrowest possible antibiotics of proven efficacy, to avoid selection of other species concurring. They're helped by infectivists for this. It's a field of their own, a kind of weapon expert in a lethal war against an invisible and extremely adaptable enemy.

So, I boasted my knowledge of the subject, asking her about MRSA, which I discovered on the news when I was in the UK: and she totally blew me away, touting MRSA as a beginner, compared to Pseudomonas Aeruginosa.

The wikipedia talks about it eloquently:
P. aeruginosa is naturally resistant to a large range of antibiotics and may demonstrate additional resistance after unsuccessful treatment, particularly through modification of a porin. It should usually be possible to guide treatment according to laboratory sensitivities, rather than choosing an antibiotic empirically. If antibiotics are started empirically, then every effort should be made to obtain cultures and the choice of antibiotic used should be reviewed when the culture results are available.

So, this bacterium is incredibly quick to adapt, and in immuno-depressed patients is often fatal - so I was told.

Moreover, it can live in Diesel tanks, drinking it happily and corroding the engine (ok, not directly, but its waste do, when combusting).

I went to bed sure that I found the toughest, most dangerous little bugger around.

Nost so fast, 'cause today I visited Aetiology, and ta-dah! there's a tougher nut to crack in microbiology:

Deinococcus radiodurans, a fascinating organism that's able to withstand many different extremes: genotoxic chemicals, oxidative damage, high levels of ionizing and ultraviolet radiation, dehydration, and, as the name suggests, incredibly high doses of radiation. (We're talking high--up to 5,000 Gy without breaking a sweat, while it only takes about 10 Gy to kill a human). However, despite 50 years of study, no one's really figured out just how it does it, though some clues (such as higher levels of manganese and low levels of iron) have emerged that make D. radiodurans stand out). Over at Small Things Considered, a recent paper is highlighted suggesting that these minerals protect not the DNA from damage, but instead, the proteins:

The researchers postulated that manganese ions transform damaging superoxide radicals (which can't easily cross the cell membrane) into hydrogen peroxide, which can be excreted. Indeed, resistant cells excrete peroxide following radiation exposure.

The original site reports:

...what could eat radioactive waste? In 1956, researchers in Corvallis, Oregon were sterilizing canned meat with gamma radiation, when something unusual happened: the food spoiled. A.W. Anderson, leading the study at the Oregon Agricultural Experiment Station, was surprised. What sort of organism could survive high doses of radiation and keep on snacking? Upon closer inspection, he found a cluster of odd, thick-celled bacteria, which he called Micrococcus radiodurans. The name was later changed to Deinococcus radiodurans, but the organism had already earned a nickname: Conan the Bacterium.

So, it does not really feast on radioactive waste, but it's pretty open to everyting else:

In most ways, D. radiodurans metabolizes in a similar manner to all bacteria. It is an obligatory heterotroph, taking sustenance from just about anything it can get. In this manner, D. radiodurans acts like well-known bacteria, such as Escherichia coli or Mycobacterium tuberculosis.

Now comes the best part: where does it come from?

Since the first experiments with nuclear fission in the 1930s, quite a bit of nuclear waste has accumulated. As a result, there are now many environments where D. radiodurans may thrive. Before this time, however, radioactive materials were relatively rare. So where was Conan hanging out in the meantime? A few Russian scientists suggested in 2002 that it may have evolved on Mars, where it would have faced higher levels of cosmic radiation (Clark, 1.) Even further out in the Solar System, potential signs of D. radiodurans have been found.

Galileo’s Near Infrared Mapping Spectrometer captured a false-color image of Jupiter’s moon, Europa, (figure 6) revealing an unusual spectrum. Some have speculated that the discoloration is caused by something like Conan the Bacterium. Figure 6: A home for D. radiodurans on Europa?“Though speculative, it is conceivable that explosions of icy slush or melt-throughs ferried extremophile organisms to Europa’s surface, where they stained the ice,” wrote Kristin Leutwyler in her book, The Moons of Jupiter (Leutwyler 126.)

May be not that far. Radiation levels up there may be strong enough to kill even this tough SoB.

So, you'd think that one would refrain from modifying this little critter, for fear it escapes our control and eats us alive? After all, similar species are found in the feces of various animals, so may be it could get inside ours and turn us into puppets... scary!

No, 'cause Frankenstein is always busy, and some scientists actually managed to splice in Conan some new gene, making it resistant to high mercury levels too - courtesy of our dear intestinal friend E. Coli. The idea would be to use it to get rid of toxic waste.

By combining the radioactive resistance of D. radiodurans with the ability to process heavy metals, they created a powerful tool for the processing of toxic waste. Their goal was to create a strain of D. radiodurans that could both “confer resistance to the most common metallic waste constituents” and “transform those metals to less toxic and less soluble chemical forms.” (Brim, et al. 85.)

The experiment was quite successful, as the modified bacteria thrived in a radioactive, mercury-rich environment. Brim commented, “This remarkable genome plasticity shows that D. radiodurans is able to maintain, replicate, and express extremely large segments of foreign DNA, and that it will probably be able to accommodate the large number of gene cassettes required for bioremediation of complex waste mixtures.” In other words, if Conan the Bacterium is put to work, he does the job.

Where is Conan the Bacterium going from here? With nuclear power and weapons disposal, we are creating new habitats in which it can flourish. Is diversity in these habitats possible—or does the unique system of DNA repair indicate that it is unlikely to evolve? Perhaps, it was, until we came along to give it a job or two. We still have much to learn about the potentials and abilities of D. radiodurans. Whether it comes to the natural disposal of radioactive waste, or the simple adaptation to stress, Conan the Bacterium, is truly our ancient hero in microscopic form.

The conclusion, I have to admit, I thought of before reading it. After all, if life is that tough, there will surely be something left alive to restart even if we were to fuck up the ecosystem almost completely. Since this bacteria is so plastic, I'm betting on him as the next center of biological diversity, once we are done with the job of eliminating the present one. In Conan's view, we are just making him a favour.

Finger crossed.

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