In a study carried out over the summer, a group of volunteers drank a white, peppermint-ish concoction laced with billions of bacteria. The microbes had been engineered to break down a naturally occurring toxin in the blood.

The vast majority of us can do this without any help. But for those who cannot, these microbes may someday become a living medicine.

The trial marks an important milestone in a promising scientific field known as synthetic biology. Two decades ago, researchers started to tinker with living things the way engineers tinker with electronics.

They took advantage of the fact that genes typically don’t work in isolation. Instead, many genes work together, activating and deactivating one another. Synthetic biologists manipulated these communications, creating cells that respond to new signals or respond in new ways.