Anyone who's had the first days of an international trip ruined by "traveler's stomach" would surely relish the opportunity to bring the responsible bugs to justice. And what better way to fight these bacterial terrors than to send in your own squad of specially trained bacteria?

The Defense Advanced Research Projects Agency (DARPA) has their money on this strategy. The organization announced on June 16 that it awarded a grant for up to $4.7 million to support researchers at Harvard's Wyss Institute for Biologically Inspired Engineering in their efforts to engineer bacteria equipped with the right weaponry to take down bacterial invaders in the gut.

"This multi-institutional effort to re-program the human gut microbiome not only has implications for treating gastrointestinal illnesses, but also opens doors to new ways of treating countless other diseases that are impacted by the microbiome, which represents a vast new frontier in medicine,"  said Wyss Founding Director Donald Ingber in a statement.

Last year, researchers at the Wyss Institute figured out a way to engineer bacteria that report on the conditions inside the guts of living animals. To do this, they stuck a genetic switch in a strain of E. coli. The switch automatically flips when the bacterium encounters particular substances in its environment — causing the engineered E. coli cell to turn blue. The color then shows up in the animal's feces, indicating that the substance in question was present in its gut.

DARPA wants to take this technology a step further by engineering bacteria that don't just report on conditions in the gut — but actually take action to change them. And if it seems strange that an organization devoted to furthering the development of military technology is spending millions of dollars on engineering bacteria, just think about how many cases of traveler's stomach the military has to deal with.

"Travelers' illness is a huge problem for the military too," said Pamela Silver, a professor in the Department of Systems Biology at Harvard Medical School, in a statement. "There are lots of troops who are down for a period of time upon deployment overseas which has implications for safety and strategy — especially in the most severe cases when troops must be returned home for treatment."

To create this bacterial task force, researchers have to equip them with a genetic switch that tells the engineered bacteria there's a problem. The first sign of an attack by bacterial invaders is typically inflammation in the gut, which produces distinct chemical signatures. When the bacteria sense these chemicals, a set of specially designed genetic circuits will kick in.

Researchers are still working on developing these circuits, but the idea is that they will provide the engineered bacteria with the weapons they need to destroy the enemy bacteria without further disrupting the conditions in the gut.

Deploying a squad of these specially designed bacteria would be as simple as swallowing a pill, according to the researchers. But keeping the bacterial assassins from going rogue in the environment presents a more complex problem. The researchers plan to prevent this issue by engineering the bacteria so they only become active in the presence of specific chemicals found just in the gut.

Work on this project is slated to continue over the course of the next two and a half years. For now, international travelers will have to make do with Pepto-Bismol.

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