US researchers have used artificial intelligence to design complete viral genomes that produced functioning viruses in the laboratory. The work generated 300 candidate designs, with 16 novel bacteriophages successfully infecting and killing E. coli bacteria. Researchers say the viruses were designed to target bacteria and pose no threat to people. The study demonstrates a new capability for generative AI in biology, while experts say it also raises important biosafety questions about future uses of genome-design systems.