In August 2014, toxins from algal blooms in Lake Erie shut down the city of Toledo, Ohio's water supply, leaving half a million residents without potable water for more than two days. A new study co-authored by researchers at the University of Tennessee, Knoxville, shows that a virus may have been involved in the crisis and suggests methods for more stringent monitoring of water supplies.

Steven Wilhelm, Kenneth and Blaire Mossman Professor of Microbiology, along with UT graduate students Joshua Stough and Lauren Krausfeldt, worked with a team of 25 researchers to examine the physiological traits of Microcystis, the cyanobacterial organism responsible for scum-like algal blooms in Lake Erie. They found that it was consistent with algal blooms from 2012 and 2013 except for one thing -- the Microcystis cells had a viral infection. Typically, toxins from algal blooms are trapped within the cell until the cell dies. But virus infections can cause cells to break open, leaking the toxin into the water and subsequently into water facility intake pipes and treatment centers.

The viruses analyzed in the study infect only bacteria and do not infect humans.

"The study changes the way we think about how the toxin moves around aquatic systems and gets into water supplies," said Wilhelm, who has done work on Lake Erie since 1997. "It may help us understand how these organisms persist in nature."

The study was published recently in the journal Environmental Science and Technology.

Co-authors include Morgan Steffen of James Madison University, who began the work while transitioning from her microbiology doctoral studies at UT; Tim Davis of the National Oceanic and Atmospheric Administration Great Lakes Environmental Research Laboratory; Michael McKay of Bowling Green State University; and Gregory Dick of the University of Michigan.

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The scientists documented the viral infection by sequencing RNA from the Toledo water samples. They used computer mathematical models to simulate how the algal blooms moved through water: satellite images were used to pinpoint where the blooms were located on certain days, and computer models filled gaps in between.

"The biggest thing we're learning is that there are dissolved and particulate sources of the toxin," Wilhelm said. "We historically think of a toxin as being stuck in the cell. In this study, we have identified a way for the toxin to move from particulate to the dissolved phase."

"Particulate" is a term used to describe anything bigger than a cell -- something that is commonly collected on a filter. It is considered dissolved once it is able to slip through the filter.

The finding justifies the need for scientists and municipalities to monitor the toxin differently than they have traditionally done -- looking at the dissolved or cell-free phase rather than just the particulate stage, Wilhelm said. This would allow water management authorities to better detect the toxin before it spreads through the water supply.

"There are ways to do the dissolved phase, but they are cumbersome and not typically run by most monitoring agencies," he said. "This study stresses the need to do that."

Next steps include examining whether the viral infections play a role in controlling the population of toxic algae and continued studies on the nutrients these cells use to grow. The scientists already have made a novel observation in this study, confirming that cells were using urea as a nitrogen source.

"It's making us re-evaluate how nutrients may shape the microbial communities," Wilhelm said.

Researchers are still trying to understand why algal blooms have exploded in growth since the 1990s in bodies of water around the country and the world.

"Algal blooms are growing in intensity, severity and frequency, and we're trying to understand why," Wilhelm said. "This study is another piece of the puzzle."