How bacteria developed resistance to antibiotics

Researchers are studying how bacteria incorporate foreign DNA from invading viruses into their own regulatory processes.

London: Researchers are trying to uncover the secrets of one of nature``s most primitive immune systems by studying how bacteria incorporate foreign DNA from invading viruses into their own regulatory processes.

Thomas Wood of the Texas AnM University has shed light on how bacteria have throughout the course of millions of years developed resistance to antibiotics by co-opting the DNA of their natural enemies-viruses.

The battle between bacteria and bacteria-eating viruses has been going on for millions of years, with viruses attempting to replicate themselves by - in one approach - invading bacteria cells and integrating themselves into the chromosomes of the bacteria, said Wood.

However, things can go radically wrong for the virus because of random but abundant mutations that occur within the chromosome of the bacterium.

Having already integrated itself into the bacterium`s chromosome, the virus is subject to mutation as well, and some of these mutations render the virus unable to replicate and kill the bacterium.

"Over millions of years, this virus becomes a normal part of the bacterium. It brings in new tricks, new genes, new proteins, new enzymes, new things that it can do. The bacterium learns how to do things from this," said Woods

"What we have found is that with this new viral DNA that has been trapped over millions of years in the chromosome, the cell has created a new immune system.

"It has developed new proteins that have enabled it to resists antibiotics and other harmful things that attempt to oxidize cells, such as hydrogen peroxide. These cells that have the new viral set of tricks don`t die or don`t die as rapidly," he said.

Understanding the significance of viral DNA to bacteria required Wood`s research team to delete all of the viral DNA on the chromosome of a bacterium, in this case bacteria from a strain of E. coli.

Wood`s team, led by Xiaoxue Wang, used what in a sense could be described as "enzymatic scissors" to "cut out" the nine viral patches, which amounted to precisely removing 166,000 nucleotides.

Once the viral patches were successfully removed, the team examined how the bacterium cell changed. What they found was a dramatically increased sensitivity to antibiotics by the bacterium.

While Wood studied this effect in E. coli bacteria, he said similar processes have taken place on a massive, widespread scale, noting that viral DNA can be found in nearly all bacteria, with some strains possessing as much as 20 percent viral DNA within their chromosome.

"To put this into perspective, for some bacteria, one-fifth of their chromosome came from their enemy, and until our study, people had largely neglected to study that 20 percent of the chromosome," said Wood.

The findings were published in the journal Nature Communications.