July 13, 2011
Guest post by Viviane Callier, Duke biology
In such a competitive world, it's surprising to find examples of animals working together rather than trying to outdo one another. But, under certain conditions, even lowly bacteria like E. coli cooperate to survive and thrive.
Figuring out how they do it could help doctors fight the human infections bacteria cause.
As they eat, bacteria make juices, or enzymes, that break down their environment, the plants and rotting wood they digest. The juices fill a bacterium's surroundings, so the producer not only gets the benefit of its digestive effort, but its neighboring bacteria do too.
Alone, one bacterium can't make enough juice to break down its food, and scientists thought that the cost to bacteria to make their digestive juice independently was too high so they won't get enough benefit back in terms of nutrition and growth.
Working in groups, however, all individuals share both the metabolic cost as well as the benefit of getting nutrition. Bacteria, therefore, have to have a method, called quorum sensing, to detect if they had enough neighbors to make juice and eat, says Duke graduate student Anand Pai.
Although it made sense for bacteria to produce their juice only when there are a lot of them in a small environment, the direct relationship between quorum sensing with bacterial growth success wasn't clear, Pai says.
At least it wasn't, until he worked in the lab of biomedical engineer Lingchong You to change the genetic material of bacteria and test the idea of quorum sensing. To do this, Pai engineered three types of bacteria: one type was unable to sense its neighbors and secreted digestive juice all the time. The second never produced juice. The third produced juice only when it sensed it had a lot of neighbors.
Measuring bacteria's growth rates, Pai saw that the bacteria that couldn't sense their neighbors grew more slowly than the bacteria that never produced juice or those that produced juice only when they had a lot of neighbors.
In other words, bacteria do seem to pay a metabolic cost for producing their digestive juices. Their ability to sense their neighboring bacteria and secrete enzymes together improves their ability to grow. But, keeping bacteria from sensing each other could lead to better defenses against bacterial infections and an alternative to antibiotics.
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