In a new study published today in Nature, scientists report that viruses can harbor fully functioning, adaptive immune systems.
Bacteriophages (aka phages) are viruses that prey on specific strains of bacteria. Viruses have long been thought to be simple organisms, consisting of little more than DNA or RNA packaged in a protein envelope. This new evidence shows that viruses are much more complex than originally believed. The study focused on a phage that infects Vibrio cholerae, the bacteria strain that causes Cholera, a deadly illness characterized by diarrhea and dehydration. Cholera kills approximately 100,000 people a year. It is spread through infected food and water.
Cholera phages found in stool samples from Bangladeshi cholera patients carried genes for functional immune systems, which previously had only been found in bacteria. The researchers believe that gene flow between phages and bacteria is responsible for the presence of the genes. In order to test whether the immune system functioned properly, the researchers infected a phage resistant cholera strain with a phage lacking the immune system genes. The cholera were easily able to resist infection. However, when the resistant cholera strains were infected with phages carrying the immunity genes, the bacteria died.
This new understanding of phages could have an impact in the fight against 'super bugs' like MRSA. Phage therapy--using phages to combat bacterial infections--could be a valuable alternative to anti-biotics, especially if said phages could be bred to harbor adaptive immune systems targeted to their hosts. As of yet, more research needs to be done to understand exactly how phages acquire immune systems.