Ballast water can harbor invasive viruses, study says

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Ballast water is used to stabilize big freighters. Image: James Marvin Phelps, Flickr

By Liam Tiernan

Ballast water entering the Great Lakes may contain viruses dangerous to wildlife and humans, according to a recent study published by the American Chemical Society.

The water used to stabilize vessels may be transporting viruses from ocean water or foreign lakes to the Great Lakes, according to Yiseul Kim, a postdoctoral microbiology researcher at Michigan State University who co-authored the study with Tiong Gim Aw, Tracy K. Teal and Joan B. Rose.

Yiseul Kim. Image: Joan Rose Lab

Kim’s research involved sampling and detecting virus-like particles using a method that differs from others previously used to study ballast water. The method, called metagenomics, studies chains of viral genetic material sampled directly from the ballast tanks. The researchers then match them to known viral chains.

“Until now, studies done on ballast water have had to focus on the presence or absence of a chosen virus,” Kim said. “Metagenomics is the process of looking at all of the viral communities in a sample.”

The study revealed that the majority of virus-like particles in ballast water do not match any gene sequences in the MSU virus database. Of the virus-like particles that could be identified, the majority were bacterial pathogens, or viruses that use bacteria as a host.

“There are so many bacteria that are necessary for the environment,” Kim said. “These viruses could infect and control colonies of bacteria to the detriment of the ecosystem.”

Some of the virus-like particles matched gene sequences of pathogens that infect fish, shrimp, plants and even humans. Furthermore, the particles within the ballast water were found to be different than the particles in the harbor water. This could mean that viruses from other parts of the world can be transferred to the Great Lakes via ballast water discharge from ships adjusting their weight as they take on cargo.

“These organisms could definitely affect fishing industries and industries that rely on the Great Lakes,” Kim said.

The study shows that the ballast water from ships in the port of Duluth, Minnesota, on Lake Superior contains six virus-like particles absent from Lake Superior water. Kim and her colleagues say they believe that this means that these viruses could invade other ecosystems.

Viruses introduced to new ecosystems can wreak havoc on native wildlife. Viral hemorrhagic septicemia virus fatally affects over 50 species of fish. Known since the 1950s in Europe, the virus was discovered in salmon returning from the Pacific to Washington state in 1988, according to the Minnesota Sea Grant.

“The most important thing is that people remain informed about the dangers of non-native species in water,” said Dale Bergeron, a Minnesota Sea Grant maritime educator.

The potential of waterborne invaders, including viruses, applies to live wells and hulls of smaller vessels as well as ballast water, Bergeron said.

The study tentatively identified three such viruses that affect fish such as koi herpesvirus, a disease known to cause mass death of carp that has been present in the Great Lakes since 2004. It also identified four viruses that are known to infect and harm shrimp, such as white-spot virus.

The study could spur lawmakers to restrict ballast water discharge in the Great Lakes, Kim said. She said she believes that new policies will target microorganisms in ballast water. The study shows that it is possible for virus-like particles to travel from one Great Lake to another or even from other biomes such as the ocean, where they can reach densities of 100 billion virus-like particles per liter. Most large shipping vessels carry about 200,000 liters of ballast, according to the National Academic Press. That’s 20 quadrillion virus-like particles per ballast tank of ocean water.

California has the most stringent state policies concerning ballast water treatment, with a state standard of zero living organisms in ballast water, including virus-like particles, going into effect in 2020, according to the American Chemical Society.

Going forward, other research may use metagenomics to give insight into the diversity of virus-like particles in different ecosystems, Kim said. That awareness can give policymakers the information they need to regulate the transfer of organisms between environments.

“Until recently, people were just counting microorganisms in their water samples,” Kim said. “I want people to know that ballast water brings different kinds of organisms, and that that diversity is very important.”

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