The researchers proposed a better strategy for the bug. During E.coli's life cycle, oxygen level is not the only thing that changes -- it also experiences a sharp rise in temperature when it enters an animal's mouth. Could this sudden warmth cue the bacterium to prepare itself for the subsequent lack of oxygen? To test this idea, the researchers exposed a population of E. coli to different temperatures and oxygen changes, and measured the gene responses in each case. The results were striking: an increase in temperature had nearly the same effect on the bacterium's genes as a decrease in oxygen level. Indeed, upon transition to a higher temperature, many of the genes essential for aerobic respiration were practically turned off.
To prove that this is not just genetic coincidence, the researchers then grew the bacteria in a biologically flipped environment where oxygen levels rose following an increase in temperature. Remarkably, within a few hundred generations the bugs partially adapted to this new regime, and no longer turned off the genes for aerobic respiration when the temperature rose. "This reprogramming clearly indicates that shutting down aerobic respiration following a temperature increase is not essential to E. coli's survival," says Tavazoie. "On the contrary, it appears that the bacterium has "learned" this response by associating specific temperatures with specific oxygen levels over the course of its evolution."
Lacking a brain or even a primitive nervous system, how is a single-celled bacterium able to pull off this feat? Whereas higher animals can learn new behavior within a single lifetime, bacterial learning takes place over many generations and on
|Contact: Steven Schultz|
Princeton University, Engineering School