A new study shows that microbes like the bacteria Escherichia coli can “learn” to anticipate changes in their environment, Nature News reports.
The study found that E. coli colonies can evolve such that they associate high temperatures, like those found in the human mouth, with lower oxygen levels similar to levels in the human stomach. They “learn” to expect the drop in oxygen level when exposed to higher temperatures and change their metabolism accordingly. This ability may give E. coli an advantage over microbes that can only adapt to their immediate surroundings.
Human and other animals learn by forming new neural connections in the brain. These bacterial colonies, on the other hand, may practice associative learning by evolving changes in genetic networks.
Saeed Tavazoie, lead researcher of the project at Princeton University, says that this finding is particularly shocking. “For as long as people have been studying the behavior of bacteria, they have assumed that responses to environmental stimuli occur in an action–reaction fashion,” he told Nature News.
Homeostasis is the process of maintaining a steady internal state despite fluctuations in external conditions. Current belief holds that organisms make appropriate changes for maintaining steady state only in response to their immediate surroundings. Observing a microorganism change its metabolism in anticipation of future conditions is a new phenomenon.
For this study, Tavazoie’s team first created a computer simulation that modeled the evolution of bacteria in a colony to see if this adaptive learning was indeed possible. After deciding that this was genetically possible, the team tested their hypothesis on live colonies of E. coli.
The team shifted the temperature in the lab dishes from 25 °C to 37 °C and then from about 20 percent oxygen content to zero. This combination simulates the changes in the E. coli environment when it travels from an outside surface to a human mouth, and then into the stomach. Hundreds of generations and a few weeks later, the bacteria had “learned” to anticipate the drop in oxygen and modified their metabolisms to prepare for the coming lack of oxygen.
E. coli’s response to changing temperatures is similar to classical, or Pavlovian, conditioning. In Pavlovian conditioning, new networks develop in the brain that link the associated gene reflexes, according to Dr. Thomas Creed’s website. The most famous example of classical conditioning is Pavlov’s original experiment, in which a hungry dog was trained to salivate at the sound of a tone. Each time the tone sounded, meat powder was placed in the dog’s mouth, causing it to salivate. Over time, the dog was conditioned to salivate when the tone sounded, even in the absence of meat powder.
The important difference between the E. coli experiment and classical conditioning is that the E. coli colony’s response is genetically evolved and will stay with the colony for a long time. The dog’s ability, however, will disappear if not used and is not passed on to the next generation.
This project may help improve methods of preventing microbial infections and drug resistance, as well as industrial processes involving bacteria, such as brewing.
Further Reading
Naturenews
Pavalonian Conditioning
Tavazoie Lab at Princeton