“New Discovery: 500 Million Year-Old Bacteria Play Important Role in Evolution of Eye”

The eye has always been troublesome. Even Charles Darwin’s theory of evolution struggled to explain the evolution of that complicated eyeball. A new discovery in which more than 500 million years old bacteria play an important role now brings more clarity.

American researchers have evidence found for the exchange of gene packages between bacteria and vertebrates. Their new study focuses on a special example of this: the IRBP gene (interphotoreceptor retinoid-binding protein), which contains the code to make a protein, forms an important link in the development of the eye and the perception of light. The scientists used the computing power of the advanced computer model IQ-TREE to understand the evolutionary history of the origin of the eye in vertebrates and came across even more bacterial gene sequences in humans that were not present in our distant ancestors.

Borrowing genes from other life forms
The idea of ​​genetic cross-pollination between bacteria and vertebrates is not new. When human genes were first sequenced in 2001, scientists thought they were dealing with more than 200 ‘bacterial’ genes. However, many of these microbial genetic links did not hold up in follow-up research. Researcher Matthew Daugherty and colleagues from the University of California delved deeper into human DNA using new computer software and compared the DNA fragments with similar gene sequences from hundreds of other species. Genes that cannot be found in distant ancestors were marked as interesting. According to the researchers, these would be good candidates for jumping directly from bacteria to vertebrates. “Out of dozens of potential abnormal genes, one stood head and shoulders above the rest,” says Daugherty.

Important chain
This was the gene IRBP, which was already known as an important link for vision. The protein that can be synthesized does its work in the space between the retina and the retinal pigment epithelium (RPE), a single-celled layer on the retina that is connected to the neurosensory retina. When light strikes a light-sensitive photoreceptor, the vitamin A complexes present cause a ‘kink’, releasing an electrical pulse that activates the optic nerve. IRBP ensures that the kink in these molecules disappears and the vitamin A complex returns to its old form. IRBP is therefore essential for the vision of all vertebrates, the researchers argue.

From protein recycling to vision
IRBP most closely resembles a group of bacterial gene sequences called peptidases. These enzymes are best known for their protein recycling abilities. It is believed that a peptidase gene jumped from a microbe to an ancient ancestor of all current vertebrates more than 500 million years ago. Once this gene was encapsulated in its new location, it duplicated itself twice. After this, it lost its protein recycling function and took on a visual role by binding to light-sensitive molecules, the study says.

Not undisputed
The essential role of IRBP is not undisputed. Some biologists in the field disagree with the California researchers’ theory. But that horizontal exchange of genes takes place between completely different life forms, that is certain. When a gene sequence takes root in a new species, the evolutionary process can run off with it and sometimes completely new possibilities arise or existing skills of the recipient get a huge boost. It is a fascinating concept that will undoubtedly require much further research.