Researchers for the first time created microbes containing artificial DNA, expanding the universal genetic code that guides life. The advance one day could lead to new antibiotics, vaccines and other medical products not possible with today's bioscience. In a report published Wednesday in Nature, the scientists said they created two additions to the normal genetic code, and then prompted bacteria to incorporate these pieces of man-made DNA with few ill effects. "The cells recognized it as natural," said chemical biologist Floyd Romesberg at the Scripps Research Institute in La Jolla, Calif., who led the research group.