Jekyll and Hyde bacterium aids or kills, depending on chance

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Todd Ciche discovered how bacteria in nematodes can switch from beneficial to deadly. (view larger image)

Living in the guts of worms are seemingly harmless bacteria that contribute to the worms’ survival. With a flip of a switch, however, these same bacteria transform from harmless microbes into deadly insecticides.

A Michigan State University-led study published in the July 6, 2012, issue of Science revealed how a bacterium flips a DNA switch to go from an upstanding community member in the nematode gut microbiome to a deadly killer in insect blood.

MSU AgBioResearch scientist Todd Ciche 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, Ciche contends.

“Animal guts are similar to ours in that both are teeming with microbes,” said Ciche, an assistant professor of microbiology and molecular genetics. “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 are pathogens of bioluminescent insects (e.g., fireflies and glow worms). In their mutualistic state (co-existing with their host), the bacteria reside in the intestines of worms, growing slowly and performing other functions that aid nematode 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 that remains is what causes this dramatic transformation?

“If we can figure out why the DNA turns on and off to cause this ‘Jekyll and Hyde’ transformation, we can better understand how bacteria enter stages of dormancy and antibiotic tolerance – processes critical to treating chronic infections,” Ciche said.

Other MSU researchers who contributed to this study are Rudolph Sloup, Alexander Martin, Anthony Heidt and Kwi-suk Kim, along with scientists from Harvard Medical School, the University of California-San Diego and Yale University.

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