CHICAGO, Sept. 5 (Xinhua) -- A study by researchers at the University of Illinois (UI) found for the first time that the mechanics of how DNA is packaged inside a virus determine the course of infection.

The study has been published in the journal eLife.

And the mechanics may also apply to viruses that infect humans and other animals, the researchers said.

UI researchers used isothermal titration calorimetry, which can measure discrete changes in thermal energy in a system, to track the course of infection. In a previous study, the researchers found that the process of viral infection gives off heat. In the new study, they exposed the host bacterium, Escherichia coli, to thousands of viral particles, then monitored the thermal ups and downs that occurred as infection progressed.

They found that the infections occurred either synchronously, with hundreds of viruses injecting their DNA into the bacterium at once; or randomly, with infections occurring more slowly in an uncoordinated fashion. A closer look at the viral genetic material prior to infection revealed that the DNA packaged inside the virus tended to be more "liquid-like" in the synchronous infections but stiffer during the random infections.

The synchronous infections corresponded closely with latent infections that preserved the host, while the slower, more random process of infection led to lytic infections that killed the host.

As temperature increased, the viral DNA became more like liquid and infections were more likely to be synchronous. Increases in extracellular magnesium ion concentrations related to cellular metabolism and growth conditions also promoted synchronous infections.

Heat made the DNA molecules inside the capsid more flexible, reducing the sliding friction between them. "The DNA becomes more flexible; it has more of a fluid character," said UI pathobiology professor Alex Evilevitch, who conducted the study.

"We now understand that the mechanics of DNA packaged inside the virus directly influences the direction of infection toward a lytic or latent pathway," he said. "We think this will help us learn how to control infections and prevent them from becoming lytic. It can potentially lead to new therapies to prevent the spread of infection."

The new findings are also "good for virology," Evilevitch said.