Living in the guts
of worms are seemingly innocuous bacteria that contribute to their survival.
With a flip of a switch, however, these same bacteria transform from harmless
microbes into deadly insecticides.
In the current issue of Science, Michigan
State University researchers led a study that revealed how a bacteria flips a
DNA switch to go from an upstanding community member in the gut microbiome to
deadly killer in insect blood.
Todd Ciche, assistant professor of microbiology and molecular genetics, has
seen variants like this emerge sometimes by chance resulting in drastically
different properties, such as being lethal to the host or existing in a state
of mutual harmony. Even though human guts are more complex and these
interactions are harder to detect, the revelation certainly offers new insight
that could lead to medical
breakthroughs, he said.
"Animal guts are similar to ours, in that they are
both teeming with microbes," said Ciche, who worked with researchers from
Harvard Medical School. "These bacteria and other microorganisms are
different inside their hosts than isolated in a lab, and we're only beginning
to learn how these alliances with microbes are
established, how they function and how they evolve."
The bacteria in question (Photorhabdus luminescens)
are bioluminescent insect pathogens. In their mutualistic state, they reside in
the intestines of worms, growing slowly and performing other functions that aid nematode's survival, even
contributing to reproduction.
As the nematodes grow, the bacteria reveal their dark
side. They flip a DNA switch and arm themselves by growing rapidly and
producing deadly toxins. When the worms begin infesting insects, they release
their bacterial insecticide.
"It's like fleas teaming
up with the plague," Ciche said.
The question remains: What causes this dramatic
transformation?
"If we can figure out why the DNA turns on and off
to cause the switch between Jekyll and Hyde, we can better understand how
bacteria enter stages of dormancy and antibiotic tolerance – processes critical
to treating chronic infections," Ciche said.
More information: "A
Single Promoter Inversion Switches Photorhabdus Between Pathogenic and
Mutualistic States," by V.S. Somvanshi et al.,Science, 2012.
Provided by Michigan State
University
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