By Ed Yong

Salmonella bacteria are best known as a causes of food poisoning and typhoid fever. Every year, they sicken millions of people. But those in Jeff Hasty’s lab at the University of California, San Diego, are different. They’ve been neutered and modified so that rather than causing gastro-catastrophes, they kill tumors.

Hasty’s team has engineered the microbes to produce a variety of anti-cancer drugs, and to self-destruct when they reach a certain density. In their death throes, the bacteria release their toxic payloads to kill the tumor cells around them. “It’s like a kamikaze mission,” says Hasty. But not all the bacteria die. About 10 percent of them survive and can re-seed the population, triggering many more rounds of self-destruction and drug delivery.

These engineered microbes have only been tested in laboratory cells and mice. Needless to say, there are many unresolved questions about safety and efficiency, and this preliminary approach is a long way from being a legitimate cancer treatment.

But that’s almost not the point. What Hasty has created is a probiotic on a timer—or rather, with a snooze button. He’s proved that it’s possible to engineer bacteria to produce and release drugs at regular intervals, to the beat of a genetic metronome that he can set. That’s useful not just for cancer, but for diseases like diabetes and high blood pressure that require regular doses of medicine. “It’s going to open up opportunities more general than cancer,” says Hasty. It’s part of a growing number of attempts to turn the bacteria that share our lives—the microbiome—into medical assistants.

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