Viruses carry thousands of bacterial genomes

Last week, we looked at a new lesson on the origin of complex cellswhich showed that the germs of our ancestors were made from fragments of several species. It sheds light on a phenomenon known as horizontal gene transfer, in which genes from one species are incorporated into closely related species. The abundance of cross-linked genes means that, in addition to the fine branching trees that connect species and common descendants, there are small threads connecting distant branches of the tree of life.

It is easy to see why horizontal gene transfer is common among viruses. They often reside in critical areas that may contain the DNA of dead and damaged cells. In addition, bacteria and archaea do not have a membrane between their DNA and the rest of the cell, making it easier for environmental DNA to find its way into the genome.

However, a new study this week shows that horizontal gene transfer is more common even among animals. And it does so by examining the genomes of many species of cockroaches, which have harbored bits of bacterial DNA for millions of years.

Going horizontal

Even bacteria or archaea store their DNA in a nucleus-like structure. Therefore, any DNA that finds its way inside the cell can be mixed with the genome and permanently integrated. That endless splicing is often aided by DNA damage repair enzymes, which sometimes “repair” the damage by replacing any DNA they can find in the cell.

Another reason that horizontal gene transfer is a major factor among germ cells is that they do not have dedicated cells. If foreign DNA is inserted into the genome of any cell, it will be inherited by that cell’s descendants. In contrast, in many animals, any foreign DNA incorporated into the genome of a liver cell will not inherit anything. Therefore, you not only need to take foreign DNA into the nucleus, but it also needs to get inside the right cell.