( enome is expected to grow by an average...)Researchers predict infinite genomes

"We were surprised to find that we haven't cornered this species yet," says Tettelin, lead author of the PNAS paper. "We still don't know--and apparently, we'll never know--the extent of its 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.

The pan-genome is more than mere syntax. The concept has real implications for molecular biology. Many important pathogens--including those responsible for influenza, Chlamydia, and gastrointestinal infections, all under study at TIGR--contain multiple strains with specific genomes. By bringing a pan-genome perspective to the study of these organisms, scientists may better learn how new pathogens emerge and better target therapies to specific conditions. One approach is to spotlight a species's core genome. On the flip side, scientists may eliminate a core genome, hunting instead for fringe genes that explain a specific strain's unique activity.

TIGR researchers say the pan-genome concept also underscores the limits of traditional known genomes. Researchers often refer to a "type" genome to describe a given species. That singular, representative genome is often simply the strain easiest to acquire from nature or grow in the lab. Yet scientists worldwide routinely tap these known genomes in public databases to hunt for drug targets, explain ecological niches, and chart evolution. How well do these microbial genomes reflect reality?

As comparative genomics itself evolves, Fraser expects TIGR to increasingly focus on pan-genomes. Many questions remain. Although some microbial species, such as GBS, have infinite pan-genomes, for instance, others
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Source:The Institute for Genomic Research