Friday, October 9, 2009

Deadly Mutant Bugs from Space!

Do we have a destiny to explore space, or should we leave it to expendable but increasingly capable robots? This perennial debate was inflamed by the recent conclusions of the Augustine Commission that the current budget was woefully inadequate for getting people to Mars.

But what about the science? Last month, NASA released a report describing more than 100 science experiments done on the International Space Station over the past eight years. I was surprised to see that "advances in the fight against food poisoning" were listed first among the accomplishments:

"One of the most compelling results reported is the confirmation that the ability of common germs to cause disease increases during spaceflight, but that changing the growth environment of the bacteria can control this virulence."

I wrote about the original research for Scientific American (subscribers only) in 2007. If this is the poster child for space research, maybe we should stay home.

Don't get me wrong, this is interesting and surprising research. But several aspects of the work deflate its global significance.

First, note the word "confirmation": The researchers had already demonstrated, in labs on Earth, the increased virulence of Salmonella Typhimurium, which causes food poisoning. They did this by building a special chamber to simulate the microgravity environment. It's important to confirm the results in real space flight, but it didn't really show any surprises.

You may wonder why there would be any effects at all from gravity, which is a very weak force. The electrostatic force between two electrons, for example, is more than 1042 times stronger than the gravitational force at the same distance.

Of course, if you fall off a building, gravity is plenty strong. But if a bacterium fell off a building, it would just float away. The strength of gravity is proportional to the mass of an object, and thus to its volume. As nanotechnologists know from painful experience, other forces like surface tension and fluid viscosity--which depend on surface area, not volume--become much more important as things get smaller. For a micron-sized bacterium, these forces are perhaps a million times larger, relative to gravity, than in a meter-sized person. So the bacterium simply can't directly detect the difference between a really tiny gravity force and none at all.

What the bacterium can detect is the flow of the surrounding fluid. Gravity (through convection) is one of many things that helps stir things up. (Growing crystals in this quiescent environment has often been invoked as another reason to do science in space.) So if you construct a special chamber where the other stirring is absent (as the researchers did), then a little gravity makes a difference.

What kind of difference? Some news stories at the time talked about microgravity causing mutations. This is just wrong. What happened was that the new, ultrastill environment switched the bacteria into a new way of expressing the genes they already had, turning some on and some off. This made them more virulent, by a factor of three, to chickens.

Why would this happen? Lead researcher Cheryl Nickersen speculated to me that the ultrastill microgravity environment might resemble the sheltered environment the bacteria ordinarily encounter, for example, in remote nooks and crannies of the digestive tract. The new expression profile could reflect the ordinary switch they make as they move from the rough-and-tumble of the outside world and the churn of the stomach and prepare to do their dirty work.

The researchers found some active genes that are normally associated with formation of the dense mats known as biofilms. Microgravity could help jumpstart this process by switching their expression ahead of time--although that might also make the critters less successful getting to the intestine in the first place.

So low gravity creates a quiescent fluid (which can also be recreated in the laboratory) that mimics normal conditions that cause salmonella to activate its natural program to settle in for the long haul as a biofilm. This is all interesting, and could be useful. In fact, a company called Astrogenix is now touting the space research as a route to a salmonella vaccine, and has sent further missions on the shuttle to test it.

But doesn't it seem like there might be more direct (and cheaper) ways to learn these things?


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