Viruses could adopt their own immune system showing that they are the living organisms

Artist's depiction of bacteriophage (Credit: iStockphoto)Researchers have found that viruses could adopt their own immune systems that can protect them from the harmful responses of bacteria.

This research has been published online in the journal Nature.

Researchers worked on bacteriophage (bacteria-infecting virus) and cholera bacteria. They found that the virus uses the immune system of bacteria against bacteria. This response of virus causes the cholera bacteria to be killed resulting in the production of more phage viruses leading to the killing of more bacteria.

In the study, researchers were working on the DNA sequences of phages taken from the stool samples of the patients with cholera in Bangladesh. They identified the genes of functional immune system in phages that were previously found in some bacteria. In order to confirm this finding, researchers exposed the phage virus resistant bacteria to the phage viruses having no such genes and found that the phage viruses were unable to kill the bacteria while in another experiment they exposed the resistant bacteria to the phage viruses with such genes and found that the virus was able to kill the bacteria. This experiment showed that the phages adopted functional immune systems to protect them from bacteria.

Researchers are very optimistic that this finding can help in further use of viruses in phage therapy in which viruses are used to kill bacteria, therefore bacterial infections, especially those  bacteria which are resistant to almost all currently available antibiotics.

“Virtually all bacteria can be infected by phages. About half of the world’s known bacteria have this adaptive immune system, called CRISPR/Cas, which is used primarily to provide immunity against phages. Although this immune system was commandeered by the phage, its origin remains unknown because the cholera bacterium itself currently lacks this system. What is really remarkable is that the immune system is being used by the phage to adapt to and overcome the defense systems of the cholera bacteria. Finding a CRISPR/Cas system in a phage shows that there is gene flow between the phage and bacteria even for something as large and complex as the genes for an adaptive immune system,” Kimberley D. Seed, Ph.D., First author and a postdoctoral fellow in Camilli’s lab, said in a statement.

Last month, scientists published the finding in the journal Science about the usage of this system (CRISPR/Cas system) for the development of a new genome editing technique with high precision.

“The study lends credence to the controversial idea that viruses are living creatures, and bolsters the possibility of using phage therapy to treat bacterial infections, especially those that are resistant to antibiotic treatment,” said Andrew Camilli, professor of Molecular Biology & Microbiology at Tufts University School of Medicine and member of the Molecular Microbiology program faculty at the Sackler School of Graduate Biomedical Sciences at Tufts University.


Kimberley D. Seed, David W. Lazinski, Stephen B. Calderwood, Andrew Camilli, (2013). A bacteriophage encodes its own CRISPR/Cas adaptive response to evade host innate immunity. Nature, doi: 10.1038/nature11927

Le Cong, F. Ann Ran, David Cox, Shuailiang Lin, Robert Barretto, Naomi Habib, Patrick D. Hsu, Xuebing Wu, Wenyan Jiang, Luciano A. Marraffini, Feng Zhang, (2013). Multiplex Genome Engineering Using CRISPR/Cas Systems, Science, doi: 10.1126/science.1231143

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