Indifferent to textbook dogma, some researchers have long suspected that bacteria really do have sex. They merge their genomes, research suggests, possibly by whole-cell fusion. Investigators liken the phenomenon to egg fertilization and distinguish it from conjugation, in which bacteria pass along bits of genetic material. A decade ago, Jean-Pierre Gratia, now at the Pasteur Institute of Brussels, Belgium, reported that mixing two nonconjugating Escherichia coli strains produced cells with both phenotypes, apparently diploid carriers of precursor genomes.