The MSU scientists downloaded the already-sequenced bacteria genomes from a variety of sites on the Internet. Then they did some cross-card catalogue comparisons.

To their surprise, many bacteria that are considered members of the same species by the current mix and match approach, often share as few as 65 percent of their genes. Humans, in comparison, share 75 percent of their genes with fish.

No one's calling for the species rules to be rewritten so that humans are lumped with their distant underwater relatives. And when it comes to bacteria, the authors say, the current species definition appears to be too liberal.

Much of the differences between genetically-similar bacteria appear to be the result of environmental pressures. E. coli bacteria, for instance, exists everywhere from the intestines of warm blooded animals to paper mills. Any new way of tallying up bacteria species should "accommodate the ecological distinctiveness of the organisms," the authors write.

"The point is about the value of a correct understanding of species people expect a species to have certain traits and live in certain habitats," said Tiedje, whose work is also supported by the Michigan Agricultural Experiment Station. "If the species definition is not reasonably predictive of this, then it loses its value. This can be important for pathogen identification, quarantine or biotechnology, for example."

Konstantinidis and Tiedje also noted that even bacteria with genetic card catalogues that were as much as 99 percent similar had enough outward differences to be separate species. This shouldn't come as a shock. Humans and chimpanzees, in comparison, share 98.7 percent of their DNA. But that small difference at the genetic level results in a big difference when it comes to outward appearance and Konstantinidis and Tiedje's work is supported by the Bouyoukos Fellowship Progr
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Contact: Jim Tiedje
tiedje@msu.edu
517-355-0271
Michigan State University
8-Feb-2005