Viruses are likely the most numerous biological entities on Earth, yet, despite over a century of studying them, researchers still have major questions: Are they living organisms or a type of replicating chemical compound? What did they evolve from? And just how many types are there?
Chemical engineering undergraduate student Tianyi “Herry” Jin and his advisor, John Yin, a Vilas Distinguished Achievement Professor in chemical and biological engineering, recently unraveled some lingering questions about viruses. They investigated one-step growth behavior, or how long it takes from the time a virus enters a host cell to the time it releases copies of itself, to see if there were any correlations with the size or growth rate of the host cells. Their answers were published on Feb. 22, 2021 in the journal Integrative Biology.
Viruses need a host cell to replicate; essentially, they hijack the mechanisms of the cells to create more copies of themselves. There are millions of types of viruses infecting all sorts of cells, including simple bacteria, complex vertebrates, and every type of living being in between. Those cells come in many different sizes and divide on many different time scales, from tens of minutes to a week. The researchers wondered if any characteristics of the host cells would impact the replication rate of the viruses infecting them.
“The largest cells are one million times larger than the smallest cells. We thought maybe there would be a pattern,” says Yin. “Maybe the largest cells would make a lot more virus.”
Collecting data on viruses meant combing through a massive mountain of literature on virus reproduction from the last 70 years, a task that fell to Jin.
“It was my first time doing real research,” says Jin, who graduated with a bachelor’s degree in chemical engineering and mathematics in August 2020 and is currently a PhD student at MIT. “There’s, like, an infinite number of papers online. So, I had to work hard to find the relevant research.”
At first, Jin collected data about a dozen types of viruses of various sizes and plotted the data. The information was compelling, and Yin asked Jin to dig even deeper. Eventually, Jin collected data on more than 100 virus-host pairs, including viruses of bacteria, humans and even obscure marine algae.
“I think the project grew into something I didn’t imagine from the beginning,” says Yin. “We started looking at a limited class of viruses. But we knew they impacted all types of life, including the most exotic. Herry was able to find and analyze the data, and we began to see patterns emerge.”
What the data shows is that the replication rate of a virus is about the same as the time it takes for a healthy cell to reproduce. So, for instance, a cell that normally takes about 30 minutes to divide will take about 30 minutes to replicate a virus, and one that takes a week to divide will take about a week to produce virus. That could be useful in calculating how quickly a virus can replicate and spread after infection.
Yin says the finding may be intuitive for virologists and in line with what many would assume. However, he doesn’t believe it was ever previously investigated in such depth. “I would love to see this in textbooks in the future,” says Yin. “It’s a pattern across all biology and it’s logical. I’m hoping others will embrace it.”
Whether or not future virology students read about his work, Jin is happy to have had the experience of working with Professor Yin. “The project helped me build research techniques like data management and literature search,” he says. “I think the most important thing was developing communication, presentation and writing skills. I presented at a virology seminar on the UW-Madison campus and at the AIChE annual meeting, and they were both very good experiences.”
Author: Jason Daley