More than 100 million landmines lay hidden in the ground around the world, but glowing bacteria may help us find them, according to a new study. The approach relies on small quantities of vapor released from the common explosive TNT. Previously, researchers engineered Escherichia coli (pictured), a bacterial species abundant in the environment and in mammalian intestines, to glow green upon detection of DNT, a byproduct of TNT. In a study published in Nature Biotechnology today, the same team reports on a small field test with mines buried in sand and soil, whose triggering mechanisms were removed. The scientists loaded about 100,000 DNT-detecting bacterial cells into a single bead made of polymers derived from seaweed and sprinkled these beads over the landmine site at night. Twenty-four hours later, they used a laser to remotely detect and quantify fluorescing bacteria from 20 meters away, mapping the location of the landmines. The researchers tell Science that they have since improved their system to detect the explosives in only 3 hours and are programming the bacteria to have a limited life span to ease qualms about permanently releasing genetically engineered microbes in the environment. The team is careful to note that its trial was preliminary. For now, the technique is limited to small areas, but in the future a faster laser attached to a drone could scan larger swaths of land. The bacteria will also need to be optimized to find mines buried in rougher terrain, or ones that use explosives besides TNT.