For the first time, scientists are looking at the abundance of viruses in one of the Great Lakes. Minnesota Sea Grant researchers Randall Hicks, associate professor and head of the University of Minnesota Duluth's (UMD) Department of Biology, and Mark Tapper, a UMD graduate student, recently completed a study that began to address how global climate change may affect viruses in the waters of Lake Superior. Because of the difficulty of identifying and counting these microscopic particles, little is known about the abundance of viruses or how various environmental factors affect them.
"We wanted to determine how many dormant viruses infect bacteria in the lake so we would have some idea of what the potential problems might be if UV light does increase as a result of thinning of the ozone layer," said Hicks. "Some types of UV light can damage DNA and can also cause dormant viruses to become active. If there are many dormant viruses, we might see major impacts on bacterial populations and, in turn, nutrient cycling and food webs," said Hicks.
Hicks and Tapper collected water samples from Lake Superior in the spring, summer, and fall of 1993, then counted the number of free viruses in the water samples. They also exposed other water samples to UV light in order to activate and count dormant viruses.
They concluded that less than 7.5 percent of the bacteria in the samples contained dormant viruses. Even if all these dormant viruses were triggered, this level of infection does not appear to be a significant threat to bacterial populations.
But that doesn't mean the research is done. As Hicks explained, "We're better able to see and recognize more viruses now that we have better technology for observing them." So this project was just a start. To build a more complete and accurate picture of the universe of aquatic bacteria and their viruses, researchers will have to study other freshwater lakes as well as the oceans. This Sea Grant-funded research has already stimulated similar studies in coastal oceans in other parts of the world.
The results of this research project were published in the January 1998 issue of the journal "Limnology and Oceanography." To find out more, you can order a reprint of the article, "Temperate Viruses And Lysogeny In Lake Superior Bacterioplankton," from Minnesota Sea Grant by calling 218.726.6191.
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