Last month, I wrote a feature for New Scientist about smart probiotics—bacteria that have been genetically programmed to patrol our bodies, report on what they find, and improve our health. Here’s how the piece began:

“[There’s a] growing club of scientists who are tweaking our microbiome—the microbes that live in or on our bodies—in pursuit of better health. They are stuffing bacteria with circuitry composed of new combinations of genes, turning them into precision-targeted micro-drones designed to detect and fix specific problems.

Some lie in wait for pathogens like P. aeruginosa or the cholera bacterium Vibrio cholerae, releasing lethal payloads when they have the enemy in sight. Some use the same tactics to attack cancer cells. Others can sense signs of