Space Odyssey, Salmonella Style

It would take a brave person to question a paper signed by 41 authors, especially when they performed an amazing experiment on gene activation in space. In fact, given the difficulties of carrying out such an experiment, any criticism would be downright churlish. Nevertheless...

Credit: Records of the U.S. Information Agency, National Archives.

A recent report shows that Salmonella enterica var. Typhimurium growing on board the Space Shuttle changes the expression of some 160 genes, with the RNA-binding protein Hfq in command. Back on Earth, the bacteria that went on this ride were more virulent in a mouse model and made more extracellular matrix. Besides the intrinsic interest, this finding may eventually help avoid infectious hazards for astronauts.

So, what's the issue? The authors compared the space-grown cultures with those grown under "identical conditions" on the ground. The quotation marks indicate our audacious attempt to ask the question: "how can one carry out controls for a space experiment?" The authors cannot be faulted for not trying, but one wonders if all the steps and manipulations can be faithfully copied. Perhaps some day they may be able to carry out a control experiment in space at normal gravity. We bet they thought of that.

Comments

[Christophe Sandt]

Further information on the experimental approach:

As a synchronous control experiment back on Earth, Nickerson’s team grew an identical set of bacteria in the same type of tubes used for flight, and incubated them in a special room at the NASA Kennedy Space Center called the “orbital environmental simulator.”

“This simulator is linked in real-time to the shuttle, and duplicates the exact temperature, humidity and growth conditions of the shuttle, with the exception that they are not flying in space,” Nickerson says. “In addition, we were also linked via real-time telecommunications with the shuttle crew when they were activating and terminating our experiments in flight, and we did the exact same things at the same time to the ground samples that the astronauts did to the flight samples – thus, we had perfectly matched, synchronous ground controls.”

http://asunews.asu.edu/20070924_microbes

[Christophe Sandt]

Wouldn't a simple centrifuge be a good way to obtain a constant acceleration (gravitational field) for a planktonic culture in the space shuttle ?

[John Trawick]

Given how costly it is to launch a space shuttle, the several thousand dollar cost of genome resequencing would seem to have been a good idea. Too bad.

There may have well been other stresses besides zero G and radiation.

Finally, I am curious as to how stable the phenotype of increased virulence was; do the bacteria loose it gradually, rapidly, or stay virulent (obviously, I haven't read the paper)?

[Alan Dove]

Besides gravity, which is clearly the focus of this paper, they really should control for a less obvious but potentially much more important factor: radiation. Our atmosphere shields us from an enormous amount of the stuff. The bacterial cultures that flew got exposed to much higher levels of radiation than the cultures that stayed on the ground, so it's entirely possible that the increased virulence is due to a mutation and/or general stress on the DNA repair machinery.

I suspect the reason they didn't look at this is that it was much easier to do gene expression chip profiling, rather than doing whole-genome sequencing on both cultures. A classic case of looking for one's keys under the lamp because that's where the light is.