The draft human genome: Bacterial footprints 28/2/01. By Richard Gallagher and Carina Dennis Remarkably, a couple of hundred genes found in humans are more similar to bacterial genes than to anything seen in yeast, worm, fly or plants.

And they appear to have been transferred from a range of bacterial species. The same genes are found in other vertebrate species, indicating that they were introduced into the genome of a common ancestor and were retained during evolution of the vertebrate lineage.

Is this a case of bacterial genes hitchhiking an evolutionary ride, or is there something in it for us? Most of the inherited genes encode enzymes and have been sequestered into specific pathways, such as stress responses and metabolism of environmental chemicals, suggesting that they have been adapted to important physiological functions.

The relatives of the gene encoding monoamine oxidase (an enzyme of the mitochondrial outer membrane), for example, appear to be bacterial in evolutionary origin. Monoamine oxidase is involved in the metabolism of neurotransmitters, and is a target for important psychiatric drugs.

The physiological functions in humans of the other bacterially derived genes remain to be determined.

Image credit: David Gregory and Debbie Marshall