Researchers might never fully describe some bacteria and viruses–because their genomes are infinite, according to scientists at The Institute for Genomic Research (TIGR), writing in the September 19-23 early online edition of the Proceedings of the National Academy of Sciences (PNAS).

With collaborators at Chiron Corporation, Harvard Medical School and Seattle Children’s Hospital, they compared the genomic sequence of eight isolates of the same bacterial species, Streptococcus agalactiae, and discovered a surprisingly continual stream of diversity.

To interpret this infinite view of microbial genomes, Tettelin and colleagues propose describing a species by its “pan-genome”: the sum of a core genome, containing genes present in all strains, and a dispensable genome, with genes absent from one or more strains and genes unique to each strain.

Source: The Institute for Genomic Research news release