Individual strains of the bacterium Streptococcus agalactiae show so much diversity that sequencing even hundreds of genomes may not reveal all the genes present in the species, according to a study published in last week's early online edition of the Proceedings of the National Academy of Sciences (PNAS). This variation likely arises because bacteria easily take up DNA from their environment, through horizontal gene transfer and bacteriophage infection, according to the study's authors. The new report also suggests that current methods of characterizing bacterial strains may not capture their genetic relationships.