UT Scientists Discover New Hidden World of Giant Viruses in Seawater

Steven Wilhelm

An international team of researchers including UT faculty has discovered a hidden world of giant viruses within a teaspoon of seawater.

The findings could help scientists directly examine the genetic potential of a virus without first having to grow it in a lab. This ability would be especially helpful for researchers in environmental and medical fields as well as virologists, as it would allow them to more rapidly identify and screen the molecular biology of new viruses.

Using a newly developed technique called single virus genomics—looking at a single virus particle instead of extracting DNA from millions of viruses to sequence a genome—researchers have picked out individual virus particles from seawater collected from the Gulf of Maine and analyzed their genomes. Through their work at the world-renowned Single Cell Genomics Center at the Bigelow Laboratory for Ocean Sciences in Maine, they discovered that every giant virus they analyzed was different and previously unknown to science. Some of the genomes revealed new infection mechanisms or enzymes not previously observed in viruses.

Giant viruses are a new group of virus particles that are larger, both in size and genomic content, than traditional viruses.

The results were recently published in the International Society for Microbial Ecology Journal, a division of the Nature publishing group.

The UT team members are Steven Wilhelm, Kenneth and Blaire Mossman Professor of Microbiology; Gary LeCleir, research assistant professor; and Mohammad Moniruzzaman, a former microbiology graduate student.

The team also included researchers from the Bigelow Laboratory, the National Institutes of Health, and two United Kingdom-based institutions—the Sir Alister Hardy Foundation for Ocean Sciences and Plymouth University.

The use of single virus genomics is a new way to obtain genomic sequence information from aquatic viruses. The term “viral dark matter,” a reference to the unknown genetic codes associated with observed effects, is often used in conjunction with aquatic viruses. These viruses—which account for 100,000,000 particles per liter of seawater—have massive effects in the ocean but are difficult to observe and even more difficult to measure. Single virus genomics can provide scientists with a new tool that will open up a universe of possibilities in understanding viruses.

Most of the newly discovered viruses belong to a group called the mimiviruses, because they mimic bacteria to persuade their hosts to eat them. Once ingested, the mimiviruses infect their hosts.

Many of the previously characterized mimiviruses have been isolated using an easily cultivated human pathogen—an amoeba that is unlikely to be the mimiviruses’ natural host in the ocean. One challenge marine scientists still face is that of determining what the natural hosts of these marine mimiviruses actually are. With clues in the genomes of individual viruses, tools developed in the study will help to address this challenge. In addition, exploration of these genomes will identify novel and diverse metabolisms of the newly discovered viruses.

“Linking individual viruses to individual hosts in nature is challenging,” Wilhelm said. “Given the size of these viruses, just confirming what their genome contains can be a challenge. With this approach we feel reconstruction of individual giant virus genomes directly from seawater is now possible. With this data, we can then infer the numbers and kinds of viruses that inhabit a particular ecosystem.”

CONTACT:

Steven Wilhelm (865-974-0665, wilhelm@utk.edu)

Lola Alapo (865-974-3993, lalapo@utk.edu)