© cup.uni-muenchen.deViral DNA
Thomas Wood, study leader and professor in the Artie McFerrin Department of Chemical Engineering at Texas A&M University, along with a team of researchers, have researched bacteria's method of using DNA from invading viruses to build a resistance to antibiotics, which revealed the secrets behind how nature's earliest immune systems worked and how it affects humans today.
What Wood and his team studied was viral DNA, which is a virus that contains DNA as its genetic material. For millions of years, viruses have had the option to replicate by trespassing into bacteria cells and merging with the chromosomes of the bacteria. The bacterium then makes a copy of its chromosome, which now contains the virus particle, and the virus acts as a ticking time bomb as it replicates itself and kills the bacterium. This isn't always the case, though. Sometimes, random mutations occurring within the bacterium chromosome can cause the virus to mutate as well when integrated into the chromosome. The mutations can make the virus unable to replicate, hence, the bacterium wins this round.
While studying these processes, Wood found that the bacterium is able to both escape death-by-virus, and perform better than bacteria that does not contain viral DNA. The bacterium with viral DNA has new "tricks," new enzymes, new proteins, new genes, etc. With all this new gear, the bacterium is able to do things that bacteria without viral DNA cannot.
"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," said Wood. "It has developed new proteins that have enabled it to resist 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."
To test this viral DNA process, Wood and his team used E. coli and deleted all of the viral DNA on the chromosome of the bacterium. Nine viral patches, or 166,000 nucleotides, were cut from the chromosome, and the bacterium cell changed dramatically. The cell's sensitivity to antibiotics increased significantly. Wood noted that the chromosomes of some bacteria contain one-fifth of the virus, which amounts to 20 percent. Until this study, no one researched that 20 percent of the chromosome because scientists believed viral DNA was harmless.
"Our study is the first to show that we need to look at all bacteria and look at their old viral particles to see how they are affecting the bacteria's current ability to withstand things like antibiotics," said Wood. "If we can figure out how the cells are more resistant to antibiotics because of this additional DNA, we can perhaps make new, effective antibiotics."
This study was published in Nature Communications.
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