( TIGR scientists probe new pan-genome ...)Researchers predict infinite genomes

Ever since the genomics revolution took off, scientists have been busily deciphering vast numbers of genomes. Cataloging. Analyzing. Comparing. Public databases hold 239 complete bacterial genomes alone.

But scientists at The Institute for Genomic Research (TIGR) have come to a startling conclusion. Armed with the powerful tools of comparative genomics and mathematics, TIGR scientists have concluded that researchers might never fully describe some bacteria and viruses--because their genomes are infinite. Sequence one strain of the species, and scientists will find significant new genes. Sequence another strain, and they will find more. And so on, infinitely.

"Many scientists study multiple strains of an organism," says TIGR President Claire Fraser. "But at TIGR, we're now going a step further, to actually quantify how many genes are associated with a given species. How many genomes do you need to fully describe a bacterial species?"

In pursuit of that question, TIGR scientist Hervé Tettelin and colleagues published a study in this week's (September 19-23) early online edition of the Proceedings of the National Academy of Sciences (PNAS). In the study, TIGR scientists, with collaborators at Chiron Corporation, Harvard Medical School and Seattle Children's Hospital, compared the genomic sequence of eight isolates of the same bacterial species: Streptococcus agalactiae, also known as Group B Strep (GBS), which can cause infection in newborns and immuno-compromised individuals.

Analyzing the eight GBS genomes, the researchers discovered a surprisingly continual stream of diversity. Each GBS strain contained an average of 1806 genes present in every strain (thus constituting the GBS core genome) plus 439 genes absent in one or more strains. Moreover, mathematical modeling showed that unique genes will continue to emerge, even after thousands of genomes are sequenced. The GBS pan-g
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Source:The Institute for Genomic Research