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For many years, scientists focused on the green alga Chlamydomonas reinhardtii did not identify any traces of active viral presence. However, this changed when researchers from Virginia Tech explored the topic further.
Maria Paula Erazo-Garcia and Frank Aylward made a groundbreaking discovery by not only finding a virus within the algae but also identifying it as the largest known virus that exhibits a latent infection cycle, meaning it can remain inactive within the host before activating and causing disease.
“Latent infections have been recognized for quite some time,” explained Aylward, an associate professor in Biological Sciences. “Many viruses are temperate, integrating their genetic material into that of their host and lying dormant for extended periods. What sets this virus apart is its remarkable size. It stands as the largest temperate virus recorded with this unique infection cycle.”
As the lead author of the research published in the journal Science, Erazo-Garcia, who is pursuing a Ph.D. and is a member of the Aylward Lab, played a crucial role in detailing these findings.
The team utilized extensive international collaborations alongside resources from the Fralin Life Science Institute’s Genomics Sequencing Center and Virginia Tech’s Nanoscale Characterization and Fabrication Laboratory to isolate the virus they named Punuivirus.
They revealed that once integrated into a host’s genome, the virus could reactivate and generate viral particles, which were subsequently observed in healthy cell cultures.
Beyond their immediate findings, the researchers anticipate that their study will provide insights into potential biotechnological applications, especially regarding DNA delivery and integration methods, which could be harnessed for gene editing technologies.
“It’s intriguing to consider that the mechanisms we’re trying to engineer in other systems naturally occur here,” Aylward noted. “This presents an excellent opportunity to understand how viral enzymes facilitate DNA integration, which may be adapted for various biotechnological applications.”
Aylward pointed out that Chlamydomonas reinhardtii is among the most extensively researched green algae. Historical records dating back to the 1970s suggest that certain green algae cultures, despite appearing healthy, could produce viruses. Researchers theorized that latent viruses may be responsible, but verifying this was challenging due to technological constraints and concerns over environmental contamination.
Typically, when healthy algal cultures become infected, symptoms are rapid and observable; affected cells die swiftly, aggregating together and leading to a noticeable change in culture color from green to clear.
“Initially, we didn’t observe any such signs,” Aylward recalled. “The culture appeared entirely healthy. Any viral infection would remain undetected without advanced molecular analysis.”
To test for viral components within the algae, researchers employed long-read sequencing techniques, which involve the examination of extended DNA strands, focusing on a specific strain known to harbor viral elements. This effort took place in the Genomics Sequencing Center with collaborative input from the Max Planck Institute for Biology in Tübingen.
They further investigated whether the viral components were active and capable of generating viral particles, tracking the production of parent viruses in cultures from inception to stationary growth phases, resulting in the identification of a distinct population of viral particles.
“We needed to confirm its existence,” stated Erazo-Garcia, who is delving into biological sciences. “Capturing images is among the most persuasive methods to validate the presence of an active virus to the scientific community.”
The cultures provided evidence that parent viruses emerged during the late exponential and early stationary phases of host growth, revealing that only a minority of cells were active with viruses, making initial detection difficult.
Further analysis in Virginia Tech’s Nanoscale Characterization and Fabrication Laboratory confirmed the presence of viral particles in the cultures, reinforcing the concept of latent infection.
Collaboration was vital to this research; Aylward and Erazo-Garcia partnered with teams from the University of Lund in Sweden and the Royal Institute of Sea Research in the Netherlands, who reported comparable infection dynamics, as well as with colleagues at the University of Miami, whose groundwork facilitated this significant discovery.
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