Tuesday, September 25, 2007

Attack of the Killer Space Germs (or, Does Evolution Work Differently in Space?)

CNN.com reports that "germs" sent into space return home to Earth more virulent. I can't find the original PNAS article to which it refers, but this seems like a very interesting finding - a strain of Salmonella sent into orbit more easily infected mice and it took 3-times fewer bacteria to kill a host. (update: here's the PNAS paper)

The researchers have a hypothesis for this finding though it is not clear how from the CNN article why. They think that the bacteria evolved in response to the low fluid sheer shear that results from the low gravity environment. I am not able to figure out why the low fluid sheer shear would lead to a more virulent bacterium, but for some reason, the researchers have shown that over 150 genes have changed in the space-traveling Salmonella. Obviously, low gravity (and/or low sheer stress) has applied a strong selective pressure on these little critters. It would be interesting to know more about the genes that were affected.

I have a major issue with the CNN article though (which is one reason I wish I could find the PNAS article). Cheryl Nickerson, a professor at ASU, is quoted as saying:
These bugs can sense where they are by changes in their environment. The minute they sense a different environment, they change their genetic machinery so they can survive

Now, I am no microbiologist, but this statement reeks of an oversimplification of the evolutionary mechanisms at work here. It is this kind of carelessness (or bad reporting?) that helps perpetuate a misunderstanding of evolution in the general public. A scientist should be able to communicate basic evolutionary theory, especially when being quoted in a high-profile media outlet.

BTW, "fluid sheer" is not the same as "fluid shear". My biomechanics professor would be so disappointed (Sorry, Amy!)

Update: Using the correct terminology I was able to find this much more informative National Geographic article. It explains a little more about the possible mechanisms involved here (and doesn't have the same nocuous Nickerson quote)

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