It seems that the idea of rolling into a ball and playing dead in the face of an aggressive predator is not limited to the human experience. A recent study from scientists at the University of Illinois found that a species of archaea go dormant in the presence of a particular virus, waiting for the potential predator to vacate the area.
However, unlike a grizzly bear, who is a very serious threat to a balled up person lying in the woods, the virus in this instance, Sulfolobus spindle-shaped virus 9 (SSV9), is relatively harmless to the microbe.
The findings from this study were published online recently in mBio through an article entitled “Virus-Induced Dormancy in Archaeon Sulfolobus islandicus.”
The researchers found that Sulfolobus islandicus would cease to grow and reproduce, going into a dormant stage, in the presence of SSV9. Interestingly, the microbes were able to recover if the virus was removed within a 24 to 48 hour time period—otherwise they die.
“The microbe is hedging its bet,” said Rachel Whitaker, Ph.D., associate professor of microbiology at University of Illinois School of Molecular and Cellular Biology and senior author on the current study. “If they go dormant, they might die, but we think this must be better than getting infected and passing it on.”
The archaea species Sulfolobus is commonly found in acidic hot springs—an environment not usually conducive for free roaming viruses. Dr. Whitaker and her team observed that S. islandicus will go dormant in the presence of just a few viruses, whether the virus was active or inactive.
“People thought these inactivated viruses were just an accident, that they were just mispackaged,” explained Dr. Whitaker. “Now we know they are being sensed by the host so they are having an effect. People are starting to think that it is adaptive for the virus to produce inactivated virus particles.”
Another interesting feature of this archaeon is that it contains an adaptive immune system against viral pathogens through its deployment of CRISPR-Cas9 nucleases. Dr. Whitaker’s team found that cultures with intact CRISPR-Cas9 created immunity to SSV9, allowing the microbes to recover from the viral-induced dormancy.
However, the investigators are still unclear as to the molecular and cellular events that are taking place while the microbes lay dormant, with the exception that visually S. islandicus looks dramatically different during dormancy.
“We really don't understand the way that viruses affect microbes,” stated Dr. Whitaker. “There is a lot to learn. These communities are usually modeled where a virus will either kill the microbe or the microbe is resistant. But actually there are all these other subtleties going on, like dormancy, that are having a bigger impact than we understand.”
While dormant microbes are not an uncommon thing to find in soil samples or even within the gut microbiota, Dr. Whitaker and her team are eager to uncover the level of dormancy that is virally induced and how it affects microbial populations.
“Many microbes go dormant when they face environmental stress such as a change in pH or temperature,” said Maria Bautista, graduate student in Dr. Whitaker’s lab and first author on the current study. “Maybe virus-induced dormancy is something that doesn't just happen in Sulfolobus; it may be a widespread response to viruses in other environments. We don't know.”
