Scientists have used artificial intelligence to design viruses that exist nowhere in nature, and 16 of them turned out to be fully functional killers of bacteria. The work, published Thursday in the journal Science by a team at Stanford University and the Arc Institute in California, is the first time an AI model has written the complete instruction manual for a living thing. The viruses only attack bacteria and cannot infect people, animals or plants. Two researchers at Johns Hopkins, Thomas Inglesby and Moritz Hanke, noted in a commentary that the ability to write viral genomes with AI now exists, and the rules to control it do not. The models, called Evo 1 and Evo 2, work like ChatGPT, guessing which chemical letter comes next in a strand of DNA. The team, led by Stanford's Brian Hie, trained it on millions of natural genomes, then focused it on a virus called ΦX174 and its relatives. Evo produced hundreds of thousands of possible designs; researchers picked around 300, had the DNA physically made in a lab, and slipped it into bacteria, which built the viruses. The 16 that survived multiplied faster than the natural virus in some cases, and a mix of the AI-designed viruses wiped out E. coli that had already learned to resist the natural version. The researchers kept anything dangerous out of the training data, used a harmless strain of E. coli, and worked in a secure lab.