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Scientists debug human genome bacteria theory
( 2001-06-21 16:24 ) (7 )

Humans did not acquire genes directly from bacteria as previously thought, American researchers said on Wednesday.

One of the big surprises of the sequencing of the human genetic code, apart from the relatively small number of genes we have and how little we differ from other organisms, was that 223 of our genes seemed to have come from bacteria.

Scientists working for the International Human Genome Sequencing Consortium, which sequenced the 3.1 billion letters of DNA that make up humans, found genes they thought had come directly from bacteria, although they did not understand the mechanism by which they had transferred.

But researchers at pharmaceutical giant GlaxoSmithKline's research centre in Pennsylvania have debugged the theory.

They say new research shows bacteria genes did not transfer directly to humans but through common ancestors hundreds of millions of years ago.

"What we are claiming is that there is no evidence that the genes have jumped (evolutionary) steps and that bacteria have contributed directly into the human cell line, skipping through all the intermediate stages," James Brown, an evolutionary biologist, said in a telephone interview.

"All the genes that we share with the bacteria can be traced back to much older organisms," added Brown, whose research with colleague Michael Stanhope is published in the science journal Nature.

EASES FEARS OF GENETICALLY MODIFIED ORGANISMS

Brown believes the finding is important because it shows it is unlikely that infectious bacteria or genetically modified organisms (GMOs) could transfer genes to humans, which should ease some fears about GMOs.

"It's a very important scientific and public information record to set straight," said Stanhope.

The scientists constructed family trees for 23 of the contentious bacterial genes and searched more complete databases than the consortium to find matches.

They found other organisms that occurred after bacteria but before people that had some of these genes.

Brown and Stanhope work for the bioinformatics unit at the GlaxoSmithKline research centre, which uses computers to make sense of genomic sequence data.

"We're very interested in genes which are common in all infectious bacteria which are not in humans because those genes might be the most appropriate targets for antibiotics which would have the least side effects," Brown added.

Brown and Stanhope's research supports similar findings by scientists at The Institute of Genomic Research (TIRG) in Rockville, Maryland, which was published in the journal Science.

They also found no evidence that genes had transferred from bacteria to human ancestors.