Microbes are engaged in a never-ending battle, and they have ways of attacking each other as well as defense mechanisms. Viruses that infect bacteria are called bacteriophages, and it's generally thought that they can drive the evolution of bacteria. But scientists still have a lot to learn about how that happens. Bacteriophages (phages) have a lot of potential for use in the clinic, since these bacteria-infecting viruses can eliminate antibiotic-resistant infections. But if they're going to be used to their full potential, we have to know more about them.
Researchers have now investigated how bacteriophages can influence the evolution of Vibrio bacteria, marine microbes that carry a lot of diverse features in their genome that can easily move around. Mobile genetic elements are not unusual in bacterial cells, which can often easily share genes with one another. A microbe might carry its own genome as well as other pieces of DNA that can move from one cell to another.
In this study, which was reported in Science, investigators determined that there are mobile genetic elements that function to defend bacteria against bacteriophages. These genetic elements can be swapped easily among microbes, so a colony of bacterial cells can easily share resistance to a virus they may be exposed to. Other mobile genetic elements are known to carry genes that, when expressed, enable a microbe to resist the effect of an antibiotic. This work may have important implications for the use of bacteriophages as antibiotics; researchers and clinicians will have to learn how bacterial infections might respond to phages.
"Each bacterial cell has a set of defense genes that enable it to eliminate certain viruses," explained senior study author Martin Polz from the Center for Microbiology and Environmental Systems Science (CMESS) at the University of Vienna. "Our study shows that these defense genes are exchanged very quickly between bacterial cells. This is possible because they are integrated into so-called mobile genetic elements that themselves control whether and when they transfer from one cell to another."
In this work, the researchers took samples of water from the coast of New England every day, and used genetic tools to assess the relationship between Vibrio bacteria and viruses. The bacteria were found to evolve quickly during this time; in 93 days, the bacteria gained significant resistance to phages in their environment within a few generations by sharing mobile genetic elements.
"This translates to bacteria being able to develop resistance to certain viruses within a few weeks to months in the wild," Polz suggested.
The researchers cautioned that the study highlights challenges posed by phage therapies. "The rapid acquisition of resistance must be taken into account in developing phage therapies, precisely because mobile gene elements similar to those we studied are also responsible for the rapid development of antibiotic resistance," Polz added.