It doesn’t take brains
to have some smarts. New research shows that even
bacteria can evolve to predict upcoming events
based on clues, like a dog salivating at the sound
of the dinner bell.
“It’s really the
first evidence that single-celled organisms —
bacteria — also have this ability for associative
learning,” says Saeed Tavazoie, a molecular
biologist at Princeton University who led the
research on E. coli bacteria.
The discovery reveals a kind
of predictive intelligence in how microbes interpret
sensory cues from their environments. Understanding
how this predictive ability affects bacterial
behavior could help scientists control microbes
better, benefiting industry and the treatment
of infectious diseases. When E. coli
enters a person’s body, its environment
immediately becomes warmer. Later, as the microbe
moves into the person’s gut, oxygen becomes
scarce. Tavazoie and his colleagues found that
warm temperatures alone triggered the microbes
to switch to a less efficient, low-oxygen mode.
The bacteria anticipated the coming lack of oxygen
and were preparing for it, the researchers reported
online May 8 in Science. This proactive behavior
challenges the view that microbes can only react
after-the-fact to changes that occur in their
environments.“Sometimes people fall into
this trap of sort of thinking that neurons are
the only game in town for learning adaptive behavior,”
comments Dave Ackley, an artificial life researcher
at the University of New Mexico in Albuquerque.
Bacteria obviously have no brains
or nervous systems. Instead, the microbes learn
through evolutionary changes in their complex
networks of interacting genes and proteins. Over
hundreds of generations, the “intelligence”
needed to predict a coming event based on present
clues becomes encoded in these networks. An individual
bacterium can’t learn this way; later generations
gain this embedded intelligence over evolutionary
time. “Of course microbes can’t tell
the future, but they can make educated guesses
about the future based on how natural selection
and past experiences have shaped their gene regulatory
networks,” comments Richard Losick, a microbial
geneticist at Harvard University.
Tavazoie’s team also showed that, over many
generations, the bacteria can “unlearn”
the link between rising temperatures and dropping
oxygen. When the scientists grew the microbes
in controlled conditions that divorced the rise
in temperature from a change in oxygen levels,
the microbes stopped anticipating lower oxygen
levels after a few hundred generations.
“This new way of thinking
about bacteria behavior is important not just
in the industrial setting where we want them to
do things, make things, but also for infectious
diseases where we want to control their growth,”
Tavazoie says. Outside of a person, many infectious
bacteria become semi-dormant, conserving energy
because environmental cues indicate that rough
times are ahead. Understanding how the microbes’
gene networks process these environmental signals
could lead to ways to trick the bacteria into
remaining in a slow-growth mode inside of people
as well.”There’s some hope that we
could engineer some changes in environment for
them, by the way we design our flu vaccines for
example, to sort of fake them out,” Ackley
says. Slowing the microbes down instead of killing
them with antibiotics could prevent the spread
of antibiotic-resistant strains of diseases, Tavazoie
says.
Source:
http://www.sciencenews.org
